B25 Valves

[2LZ]

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.

[Spaceman]

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.

[2LZ]

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.

[2LZ]

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....

[Spaceman]

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.

[2LZ]

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.

[2LZ]

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.

[Spaceman]

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.

[2LZ]

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.

[Spaceman]

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!

[2LZ]

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.

[Spaceman]

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.

[2LZ]

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.

[Spaceman]

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?

[Spaceman]

Just noticed where you are based - perhaps I can pop in to see your engine on my trip to Yosemite later this year