Hey folks.....Been all over the web. I have an early 1967 BSA B25 Starfire, meaning that the valve eccentric adjuster flat spots point "9 and 3" instead of "3 and 9". My bike is a "before C25 2050", before they reversed the eccentrics and changed the tappet cover to the new one or whatever the fine folks at BSA decided to do.
I consulted my Rupert Unit Single, Vol 1, and my Haynes, and I'm at a loss of how my eccentrics ended up lining up, after hours of trying to get them within the "grey areas". The intake simply would not have much joy in that area. I did the "spin it in and back it out 180'," method, etc....
I know over the last 56 years, others have laid their hands on my baby, so it's part of the game. Long story short, I needed a measurement instead of following Mr. Ratio's advise directly. I set them tighter than the recommended factory settings at .004 and .005. I've read this should suffice.
The intake however would not cooperate to have the flat spot inside the 9:00 range. It ended up being this....and it's perfect. The push rods spin freely.
Question: Can a later eccentric (backwards?) be fitted in an early rocker box?
First off - the early (-2050) and later cylinder heads and rocker spindles are not interchangeable. The two rocker spindles you have should be identical - if you thought you might have a later one fitted, I am sure you would see that by comparing them - as said, the eccentric direction on one would be reversed.
In principle, if you start with the inlet rocker spindle flat at 9 o'clock then you should get the full range of tappet adjustment by rotating it between 6 o'clock and 12 o'clock. It would be interesting to know how much the inlet clearance varies between these 2 limits. Rotating the spindle through 180 deg should not change the level of clearance adjustment and it is therefore difficult to see why the inlet flat ends up where it is?
Quote from: Spaceman on 10 Jan, 2023, 07:46 :
First off - the early (-2050) and later cylinder heads and rocker spindles are not interchangeable. The two rocker spindles you have should be identical - if you thought you might have a later one fitted, I am sure you would see that by comparing them - as said, the eccentric direction on one would be reversed.
In principle, if you start with the inlet rocker spindle flat at 9 o'clock then you should get the full range of tappet adjustment by rotating it between 6 o'clock and 12 o'clock. It would be interesting to know how much the inlet clearance varies between these 2 limits. Rotating the spindle through 180 deg should not change the level of clearance adjustment and it is therefore difficult to see why the inlet flat ends up where it is?
Spaceman, thank you for the response. Please forgive my error in the earlier post. Not meaning 180' (late night math typo), but I spun the spindle clockwise to the stop, then backed it out 360', then set the inlet spindle to the 9:00 position. I did the same with the exhaust spindle (tightened to the stop, the 360' back-out, then set at 3:00) and the exhaust spindle set to .005 right within it's grey range in the manual, no problems.
Anything below the 10:00 position on the inlet spindle was stiff and pushing the valve. Where the inlet spindle is set in the pic (about 1:30) is where it's exactly .004 and the push rod spins freely. That's why I was wondering if someone may have put a later spindle in the rocker box on the inlet side. I'm going to set it per Rupert Ratio's method and see where it ends up. Mind you, I did the above adjustment at TDC compression stroke, not RR's method. I'll check back after I reset again.
Your exhaust adjustment looks to be ok but the behaviour of your inlet spindle looks to be a bit odd!
What would help to clarify what is going on is to work out the direction of each spindle lobe (the direction of maximum eccentricity). For the later spindles (2050+), I believe the lobe direction is the same as the direction of each flat - if your spindles are the same, then in your pic, the inlet lobe will be at 1:30 and the exhaust lobe will be at 3 o'clock. By looking at how each rocker moves as you turn the spindle, you should be able to work out where each lobe is. Essentially, if you turn each spindle until the rocker is at its highest position this will mean the lobe is pointing vertically upwards. I suspect the corresponding flat will also be at 12 o'clock?
The way the B25 cylinder head is designed is that you have to keep within the appropriate (grey) adjustment range. If you don't, the extra sideways displacement of the rocker might cause problems with the engine and a greater amount of wear in the valve gear.
Thank you, Spaceman. Here is what I (we) worked out today. Being no Greenhorn to mechanics and motorcycles, that does not mean I am beyond being an occasional bonehead. So......I invited my 74 year old, master machinist neighbor over to read over the Haynes, and of course Rupert Ratio Vol. 1. Then we tackled the bike. He has a full understanding of the difference between the early 1967 rocker box and the ones built after January 1968 regarding proper clocking of the spindles
We performed the valve adjustment with both the "TDC" method, and also Mr. Ratio's method. Bottom line is, as you've stated the exhaust came right in to .005 in the proper grey area. The inlet, on the other hand, refused to cooperate on setting it with either technique. The grey area between 6:00 and 12:00 (9:00 being the mid point), kept the rocker binding. Not on the valve stem, but the rocker was misaligned enough for the underside of the rocker arm to push down the edge of the spring keeper to open the valve. Even with the valve opening, I could still slip a feeler between the rocker end and valve stem. We also unscrewed the spindle 360', as Mr. Ratio suggested and got the same result.
After resetting the spindle to the original position, once we past 12:00 into the 3:00 side of the rotation (Approx 2:00 as the pic shows), we were able to perfectly set the inlet at .004. This is why I think either someone replaced the inlet spindle with a post January 1968 version....or something has been machined enough (valve seat or rocker face) to swing the adjustment that far around the rotation. I guess the only way to really tell is to pull the rocker box and look......
If I understand you correctly, the pad on the inlet rocker arm is somehow pressing down on the valve collar rather than on the end of the valve stem? What is therefore happening when you rotate the flat past 12 o'clock, I assume, is that it it is moving the rocker far enough forward to stop the contact with the collar?
I'm struggling a little to picture exactly what is happening. With the inlet rocker flat at 9 o'clock, is the bottom of the rocker pad not in the middle of the valve stem? Or is it displaced far enough to be basically just be contacting the edge of the valve stem? If so, it would be interesting to know whether this is the forward edge or the back edge?
I don't really know what the difference is between the earlier rocker spindle and the later one. The lobe on your inlet spindle appears to be aligned with the flat which I believe is the same for the later spindle. All I can think of is that the operating arm on the later rocker may be slightly longer than the earlier one. If the pad on your inlet rocker is contacting the back edge of the valve stem (as seen from the front of the bike), it could well be that you have the wrong rocker fitted?
Here's a (very lousy) hand drawing of what's going on. Exaggerated but you get the idea. It's almost like I have two exhaust spindles the way the inlet spindle is cammed. Hopefully you can open the pdf.
Yikes - I can now see why you are having a problem! I will have a look at the inlet side of one of my (OIF) B25's tomorrow to see how it compares. It's not obvious what's going on!
I would have thought the geometry would have been essentially the same (except for being mirrored) for both the inlet and exhaust rockers. If the inlet side looks like the top drawings with its flat at 9 o'clock, how does the exhaust side compare with its flat at 3 o'clock - in other words, what is different?
The only thing I can think of that might cause this problem for the inlet, is if its spring collar is closer to the top of the valve stem than for the exhaust valve or the inlet valve seat has been machined in such a way that the valve stem is now higher in the cylinder head than the exhaust.
If I can get to it tomorrow, I will take a look at the geometry on my OIF B25 to see what the inlet and exhaust rocker geometry looks like and, in particular, how much clearance there is between the body of each rocker and its spring collar.
Much appreciate Spaceman. The exhaust rocker/valve relationship acts exactly as it should at 3:00 and set right at .005".
I noticed on the nut side of the exhaust spindle it looks as though someone cut a screwdriver slit in it with a Dremel, but the inlet spindle does not have that slit. Was it changed out at one time in the past 57 years???....and if it was replaced, was the correct (pre-2050) spindle used? The inlet spindle acts completely natural in the 3:00 position, like its post-2050. I wonder if these are marked with any part#'s? Taking it apart may be the only real way to tell.
Just stepping back slightly, you originally indicated that your engine number was earlier than C25-2050. This means you would have one of the first <2000 x C25 engines produced?
Having just read the BSA service sheet describing the revised cylinder head design with reversed spindles, a test of whether you have the earlier C25 version is whether the rib above the push rods is present. If you insert your finger through the push rod inspection hole, for an earlier rocker box, you should feel a traverse rib projecting down from the roof formed by the rocker cover above the push rods. If it is a modified rocker box, the roof will be smooth (ish).
The other change to the earlier rocker box assembly was to remove the spring thrust washer on the LHS. If you have had the rocker box apart, it would be good to confirm whether the spring washer was there or not. If you have a later rocker box fitted then clearly all you will need to do is to reverse the direction of the spindle flats. If you really do have a very early engine then it might be necessary to take off the rocker box and examine in more detail what you have from the numbers cast on to the various components.
Some further thoughts:
I'd assumed that the geometry for the inlet and exhaust rocker mechanisms would have been essentially symmetrical although mirrored. However, the reason given in the Service Sheet for changing the C25 rocker box assembly was to improve the symmetry. Given that the change was made after only 1950 x C25 engines, this would seem to indicate there was quite a significant problem with the earlier design that had to be put right part way through the 1967 model season.
It's possible the rocker box of the earlier engines was changed under warranty and that's what you now have. It may be that the problem was the one you are experiencing with interference from the valve collar with the rocker body and the solution was to move both rocker spindles closer together. To facilitate this, it may well have been necessary to remove the pushrod tunnel roof rib and, perhaps, to also change the length of each rocker arm.
At this stage, it would be good to find that the pushrod tunnel roof rib has been removed on your engine and you have a modified rocker box assembly.
This is the parts bulletin.
Thanks for the info guys. I'm not sure all that changed in the early rocker boxes other than cutting out the casting bridge and changing the spindles(?), or how they clock. If the location of the spindles and the rockers were also changed, I haven't been able to find any info on that.
I just checked and my rocker box has not been modified regarding having the bridge cut out (see pic). Also, mine if definitely pre-2050, and the numbers match. (frame has a B). I've also included a pic of the nut side of the spindles, so you can see the exhaust spindle has a slot for a screwdriver, and the inlet does not.
I was hoping there would be a simple solution to your problem :(
What we don't know is what problem the early C25 suffered from that caused BSA to change the design of the rocker box assembly. I assume they had to solve this problem by moving the rocker spindles further away from the valve stems by reversing their lobe direction and I assume, because the rib got in the way, they had to machine it off. As part of the re-design, they also got rid of the spring thrust washers which, presumably, were also involved in the C25 problem. Although the rocker design was changed, this may simply have been to increase their width to account for the missing thrust washer.
In order to try to understand what the original problem was, I'll have a close look at my OIF B25 tomorrow and see, in particular, what happens when I rotate the spindles through 180 deg. If their is a problem with valve collar clearance, it should show up on my B25. I'll also measure the position of the ends of the rocker spindles to compare with yours although I doubt that they would have changed.
Much appreciated, Spaceman. keep us posted on you OIF B25 findings.
If you look at the nut ends of the spindles in the above pic, the exhaust spindle not only has a slot in it, but the inlet spindle actually looks like it's longer (sticks out of the nut further), and seems slightly pointier, like a different design. I'll have to measure them and compare. Both spindles are set in their current positions from one turn out.
Have just had a preliminary look at my OIF B25. The eccentric adjuster appears to move the rocker by a total of the order of 1/8" - in other words, the difference in rocker position going from 9 o'clock to 3 o'clock is the order of 1/8".
For my B25 inlet, the correct clearance can be obtained at either 11 o'clock or 1 o'clock since moving the spindle lobe between these two positions gives the same rocker lift. I doubt if it would make much difference choosing either setting.
With the spindle at 9 o'clock giving the maximum rearwards movement of the rocker, there is ample clearance between the rocker and the valve spring and collar. The only thing that looks as though it might interfere with the spring or collar is the LH washer on the rocker spindle. There is no way the body of the rocker comes close to the spring or collar.
The key dimensions from B25 are:
Rocker spindle spacing: 3 5/16"
Spindle centre height above bottom of rocker box: 1 5/16"
Height of rear of valve spring below inspection hole: 9/16"
For my B25, the pad on the end of the rocker is in the centre of the valve stem when the spindle is CW between 12 o'clock and 6 o'clock. In the case of this earlier B25, I honestly don't think an inlet setting of 1 o'clock is going to cause any problems although I would have more confidence if I knew what was causing the interference problem with, for example, a setting of 11 o'clock. The only thing I can think of that might be the cause this is if it the inlet valve seat is significantly recessed resulting in the spring being much higher relative to the inspection cover hole than on my B25.
Quote from: Spaceman on 15 Jan, 2023, 12:17
Have just had a preliminary look at my OIF B25. The eccentric adjuster appears to move the rocker by a total of the order of 1/8" - in other words, the difference in rocker position going from 9 o'clock to 3 o'clock is the order of 1/8".
For my B25 inlet, the correct clearance can be obtained at either 11 o'clock or 1 o'clock since moving the spindle lobe between these two positions gives the same rocker lift. I doubt if it would make much difference choosing either setting.
With the spindle at 9 o'clock giving the maximum rearwards movement of the rocker, there is ample clearance between the rocker and the valve spring and collar. The only thing that looks as though it might interfere with the spring or collar is the LH washer on the rocker spindle. There is no way the body of the rocker comes close to the spring or collar.
The key dimensions from B25 are:
Rocker spindle spacing: 3 5/16"
Spindle centre height above bottom of rocker box: 1 5/16"
Height of rear of valve spring below inspection hole: 9/16"
For my B25, the pad on the end of the rocker is in the centre of the valve stem when the spindle is CW between 12 o'clock and 6 o'clock. In the case of this earlier B25, I honestly don't think an inlet setting of 1 o'clock is going to cause any problems although I would have more confidence if I knew what was causing the interference problem with, for example, a setting of 11 o'clock. The only thing I can think of that might be the cause this is if it the inlet valve seat is significantly recessed resulting in the spring being much higher relative to the inspection cover hole than on my B25.
Excellent info, Spaceman. Thanks a bunch.
I was wondering about the intake valve seat being recessed also. That would require of course, pulling the head and measuring which at the moment, isn't on the docket. Especially when it appears that this bike truly may only have around 500 miles on it. So much of the bike still looks new. Time will tell as I dig deeper.
I'm seriously considering purchasing a newer version, complete, used rocker box off of EBay, just to compare it to my older version. It would be interesting to take both rocker boxes apart and measure everything out, just for the archives here, and future reference for others who may also run into this issue.
Found a good, clean, complete rocker box from a newer B25/TR25W on EBay. Has all the washers, nuts and rocker pads look barely used. Ordered it for comparison to mine. Good price. Had to....
It would be interesting to know how far the inlet valve spring was below the lip of the inspection hole to compare with my 9/16". If the valve seat was recessed, it should then be obvious from this measurement. However, if this is a low mileage engine, the valve seat should not be that worn.
It will also be interesting to know the differences between the rocker box assemblies although I suspect they may be relatively small. The later rocker box itself may simply have had the push rod tunnel roof rib machined off and the rocker dimensions slightly changed to match the reversing of the eccentric lobes and to account for the deletion of the spring thrust washer.
Quote from: Spaceman on 16 Jan, 2023, 06:39
It would be interesting to know how far the inlet valve spring was below the lip of the inspection hole to compare with my 9/16".
I agree and hopefully tomorrow. Been a tad nippy here recently.
Made it out to the shop today.
Center of spindle to center of spindle - 3 5/16. (3.27 or 83.14mm)
Center of spindle to bottom of rocker box - 1 5/16 (1.31" or 33.3mm)
Couldn't get my caliper in the intake inspection hole for the valve spring measurement, so I used a roll-up measurin' stick. - looks like 9/16 to me.
All dimensions look to be identical to my OIF B25 and so reason for interference problem still not clear. What would help is if we can find out what the original problem was with the C25 rocker mechanism - yours might be suffering from this. Alternatively, just replace the rocker box assembly by the later one you are buying.
Quote from: Spaceman on 18 Jan, 2023, 06:17
Alternatively, just replace the rocker box assembly by the later one you are buying.
That's the plan, at this point. I have a rocker box gasket on order. Spoke with my machinist neighbor last night. We'll end up taking both boxes apart and measuring it all out to see where the discrepancies lie.
It would good to know what the problem actually is and possibly what forced BSA to change the design.
My OIF B25 is different but can you remove the rocker box on yours in situ without taking the cylinder head off? If you have to take the head off, it would be easier to then see what's going on!
Quote from: Spaceman on 18 Jan, 2023, 19:44
It would good to know what the problem actually is and possibly what forced BSA to change the design.
My OIF B25 is different but can you remove the rocker box on yours in situ without taking the cylinder head off? If you have to take the head off, it would be easier to then see what's going on!
It looks like I wont have any issues pulling the rocker box off, in bike. The newer one showed up today. At a glance I can tell you that the biggest, most obvious difference, besides the lack of casting wall, is the newer one doesn't come with a valve lifter (compression release). I'm hoping if I do find differences in the rockers and spindles, I'll be able to swap them over to the older box. I want the valve lifter since I don't believe I have the upgraded kick starter BSA installed after eliminating the valve lifter.
It would be interesting to know why BSA made all these changes to the 1967 B25. Interestingly, the 1968 parts book still shows the valve lifter and also shows the upgraded kickstart spindle so the latter does not look as though it was introduced because the valve lifter was eliminated.
Quote from: Spaceman on 19 Jan, 2023, 12:48
It would be interesting to know why BSA made all these changes to the 1967 B25. Interestingly, the 1968 parts book still shows the valve lifter and also shows the upgraded kickstart spindle so the latter does not look as though it was introduced because the valve lifter was eliminated.
Tore into both rocker boxes today. First initial findings besides the wall in the old box is, you were right Spaceman. The rockers themselves are different lengths, due to lack of spring washer. The "new" ones floated real easy on the spindles. The old ones had some resistance in their movement, due to the spring washer.
You can also see differences inn the spindles themselves. Probably for oiling, would be my guess. Odd thing is, the eccentircs never changed from the old to knew spindles. All four eccentircate (is that a word?) toward the flat spots where you adjust them. Why then would the old spindles adjust to the outsides and the newer spindles adjust to the insides???? It's not like the Mother Ship reversed the eccentric bumps. I'll do some more measuring tomorrow.
Logically, the main reason BSA reversed the eccentric direction was to provide a greater clearance between the body of the rockers and the valve springs - this lack of clearance was the cause of your original problem with the inlet rocker as I understand it.
I would have thought the two fundamental questions to be answered if you can are:
1. Why do you get interference between the inlet rocker and the valve spring with the eccentric in the original direction? As I found on my OIF B25 with reversed eccentric, there is plenty of clearance.
2. What stops you from reversing the eccentric direction in your original rocker box to solve the problem? For example, are the rocker arm lengths different for the two sets you have?
I would be intrigued to have a closer look at your engine if you were anywhere close to Oxfordshire?
Just noticed where you are based - perhaps I can pop in to see your engine on my trip to Yosemite later this year ;)
Hev yah! Yosemite is about an hour or so away.
I'm going to be measuring both sets of rockers today for differences in lengths and angles. Then I'll be assembling all the new stuff in the old boxes to see if the valve lifter interferes with anything. I'd sure like to keep it for my old right knee.
Interesting discoveries today. Not only are the new rockers longer (along the spindle) than the old ones, but the newer rocker box is machined differently, and not just the wall that needs to be removed. The end boss's that the rockers sit between are machined further apart on the new rocker box to fit the longer rockers. It's not just making up spring washer room. In short, rocker-no-fit-mahn. Interestingly enough, the new rocker box is not yet the new part number, and is still stamped 40-961.
While the difference between the new and old intake rockers seems negligible, the exhaust rockers are very different, even though both still have the flat spot for the valve lifter (see pics). I think that's the angle/reach the Mother Ship wanted to fix by upgrading. Maybe some old ones snapped because of the long reach and steeper angle???....compared to the shorter reach, and less angled new rocker? They definitely didn't run the old setup very long.
The new style rocker has a less angled and more direct hit on the valve stem. Both the new intake and exhaust rockers have the same angle of attack on the valve stems, where the old ones are different.
Well, Looks like my right knee is out of luck. Either I go back to the original complete rocker box setup with the valve lifter, or upgrade to the new complete rocker box, since the individual parts really aren't easily swapped (as the BSA TSB states. Imagine that? ::))
I can see the rocker arms appear to be different in shape but are the distances between the pads and the rocker spindle axes different? In other words, are the rockers designed for a different distance between the top of the valve stems and the rocker spindles, for example, because the spindles are reversed? I suspect the answer is that both sets of rockers are the same?
What you ideally need is a 1968 rocker box (70-7818) because that incorporated all the mods but also retained the valve lifter.
It still looks as though the fundamental question that needs answering is why, with the old rocker box set up, does the inlet rocker interfere with the valve spring with the spindle eccentric in the 6 o'clock to 12 o'clock position? If you were to assemble the later rocker box on to the head, would you still have the same problem? As said, I didn't get any interference on my OIF engine with a reversed spindle.
Although the simplest solution would be to reverse the spindles on your original rocker box, this may result in unforeseen problems. One possibility is a rocker oil supply issue which may be related to why the original spring thrust washer was deleted. If it was me, I would definitely want to get to the bottom of the interference problem. My gut feeling is that this is due to a problem with the location of the inlet valve spring rather than a problem with the rocker box?
More discoveries today. This may effect my rocker interference problem, but whoever assembled the rocker box last time did it incorrectly.
1- The spring washers were on opposite ends of the rockers. The intake rocker spring washer was on the adjustment end of the spindle. Not the drive side, throwing it out of alignment with the valve stem.
2- I was wondering why the underside of the flat surface on the exhaust rocker was worn oddly where the valve lifter cam hits it. Then I found that the washer/o-ring was on the inside of the rocker box, instead of being on the outside, pushing the lifter actuator into the rocker.
3- There were no alignment dowels between the rocker box and cylinder head! Lord only knows if the rocker box was on correctly. This could also effect rocker alignment.
I got everything cleaned, lubed, and reassembled according to Mr. Ratio. Can't wait to see what else I find. ::)
I'm truly starting to believe that Brit bikes aren't bad or unreliable. It's all the ham-fisted mutants who wrenched on them for the last 57 years.... >:( The bike and design itself is unbelievably simple.
It sounds as though a complete mechanical moron assembled the rocker box last time - without the 2 x alignment dowels, the rockers could well be misaligned and this will explain why the inlet rocker was interfering with the valve spring. Hopefully, you'll now be able to adjust the tappets as per the workshop manual?
Quote from: Spaceman on 02 Feb, 2023, 06:27
It sounds as though a complete mechanical moron assembled the rocker box last time - without the 2 x alignment dowels, the rockers could well be misaligned and this will explain why the inlet rocker was interfering with the valve spring. Hopefully, you'll now be able to adjust the tappets as per the workshop manual?
Not just the lack of alignment dowels but also the spring washer being on the wrong end of the intake spindle. That would definitely shift the rocker position.
I'm currently in touch with CBS about locating some dowels. If Pt# 60-3074 are made of Unobtainium, I'll take the one I have that was stuck in the Ebay rocker box, measure it out and buy some generic dowels. I hope whoever worked on it last didn't dive deeper into the motor..... :-\
The dowels are nothing special - I normally just machine a new one when required out of mild steel.
Quote from: Spaceman on 02 Feb, 2023, 17:23
The dowels are nothing special - I normally just machine a new one when required out of mild steel.
Measured the one and only dowel I had. Basic 8x12 dowel. Got a pair coming.
According to Mr. Ratio, the B25 has had multiple rocker box changes....and I found out by experience now, he's not kidding. It's taken me four different rocker box gasket orders to finally (almost) get the correct one. I still had to adjust two of the stud holes. The one gasket I received that had all the holes line up, had the exhaust span of the gasket run almost a mm out and wasn't sitting on the head casting correctly. Didn't want to risk the possible leak.
Not only that, but once I supposedly correctly assembled the rocker box with the spring washers being where they are supposed to live (according to the manual), once fitted, the foot of the intake rocker was not centered on the valve stem. Back apart it came. So, the end result is, I swapped the spring washer to the other end of the spindle, and the intake spindle still clocked where it was earlier.
I rotated the motor multiple times and rechecked. No interference and the adjustments held true. I'm going to run with it. Time to prime the oil system.