I bought a BSA with a B44 newly rebuilt engine. The engine started life as a B25.
Well after less than 100 miles the piston nipped up. It is on its second rebore which is a bummer.
Took it apart and piston and barrel were bone dry
The oil pump must have been doing something as the oil was returning to the tank with the usual air gaps.
How do I check the oil is making it to the big end?
Thanks.
I wonder if a new bush was fitted but the cross holes not drilled.
if I was to strip the engine to check I would use an oil can to check, as it will with a small force pump oil out of various holes.
Air lines could be used but wont show flow that an oil can would , if there is a small or blocked hole air will get through, oil pressure will back up.
Quick question. Was the mixture correct. I have done a few snipped up engines now where people err other side of caution and run a bit rich. This usually ends up with "bore wash" taking the oil off the barrel wall.
Both the B25 and B44 engines used an end fed crankshaft - this meant that the oil from the pump passed through passages in the inner timing cover into the end of the crankshaft. The oil was prevented from leaking past the end of the crankshaft via an oil seal in the cover retained by a circlip.
If this seal fails or the seal pops out because the circlip has not been inserted, the oil will leak past the crankshaft back into the sump resulting in no oil to the big-end and none to the cylinder walls. Also, it is no unknown for the seal to be inserted the wrong way round. Also, according to Rupert Ratio, if you use a B44 crankshaft with a B25 inner timing cover, the crankshaft may not project far enough to engage with the seal resulting in no oil flow to the big-end.
It sounds as though the inner timing cover will need to come off to check what is happening with the crankshaft and oil seal. Unfortunately, I'm not sure there is any easy way of testing that oil is getting to the big-end without taking off the inner timing cover first.
It is also worth checking that the oil passageway from the crankcase into the inner timing cover is not blocked. The oil from the pump enters the cover through a hole on both sides just underneath where the end of the crankshaft engages with the small oil seal. On later unit singles, there was a small O-ring between the cover and the crankcase to seal the passageway but this is not there on earlier models. If this passageway is blocked then oil will not get to the crankshaft.
Problems could be caused if the O-ring is missing or someone has blocked one of the holes inadvertently with sealant.
Quote from: chaz on 27 Oct, 2022, 20:30
I wonder if a new bush was fitted but the cross holes not drilled.
if I was to strip the engine to check I would use an oil can to check, as it will with a small force pump oil out of various holes.
Air lines could be used but wont show flow that an oil can would , if there is a small or blocked hole air will get through, oil pressure will back up.
No bushes on mine, all roller or ball bearings I believe...
Quote from: cdsdorset on 27 Oct, 2022, 22:36
Quick question. Was the mixture correct. I have done a few snipped up engines now where people err other side of caution and run a bit rich. This usually ends up with "bore wash" taking the oil off the barrel wall.
I did wonder. The plug looked good. The bottom of the piston was dry of oil as was the crank and con-rod. There was no burnt oil under the piston...
Piston seizure may becaused by being bored with insufficient piston to cylinder clearance - not unkown for an engineer used to boring liquid cooled engines to use too tight a clearance when boring an air cooled engine.
If using the B25 oil pump then it has a greater feed capacity than the B44 type, which uses a narrower gear with a thrust washer in the oil chamber on the feed side.
Looking at that picture the gudgeon pins has got damn hot. The small end is probably scrap as well.
If there is no oil around the big-end bearing area (as well as the piston) then it looks as though the oil feed to the big-end is not working, possibly for one of the reasons mentioned above. However, before you pull the timing side of the engine apart, it might be a good idea to check the oil pressure release valve is ok. Although highly unlikely, if the valve internals were missing or stuck in the open position, this would divert the oil from the pump straight back into the sump with none going to the big-end.
Quote from: Spaceman on 27 Oct, 2022, 23:04
Both the B25 and B44 engines used an end fed crankshaft - this meant that the oil from the pump passed through passages in the inner timing cover into the end of the crankshaft. The oil was prevented from leaking past the end of the crankshaft via an oil seal in the cover retained by a circlip.
If this seal fails or the seal pops out because the circlip has not been inserted, the oil will leak past the crankshaft back into the sump resulting in no oil to the big-end and none to the cylinder walls. Also, it is no unknown for the seal to be inserted the wrong way round. Also, according to Rupert Ratio, if you use a B44 crankshaft with a B25 inner timing cover, the crankshaft may not project far enough to engage with the seal resulting in no oil flow to the big-end.
It sounds as though the inner timing cover will need to come off to check what is happening with the crankshaft and oil seal. Unfortunately, I'm not sure there is any easy way of testing that oil is getting to the big-end without taking off the inner timing cover first.
Thanks for the information.
Distance from end of crank to crankcase face is 22.4mm (please see pictures)
Distance from lip of oil seal to face is 21,6. Not a lot spare...
Two other things I have noticed:
1)The inner timing cover has been machined away to fit over oil pump. Please see picture. Why did this need to be done?
2) The boss where the oil feed O-ring fits on is rather small. Barely bigger than the O-ring. Is this mismatch because the wrong parts are used?
Thanks...
The machined rib to avoid cover pressing on the pump?
See below service bulletin.
Here's a pic of the timing end of a B25 crankshaft - you can see where the oil seal contacted it. If your crankshaft is only just contacting the seal then that looks to be a problem?
Quote from: JulianS on 28 Oct, 2022, 09:52
The machined rib to avoid cover pressing on the pump?
See below service bulletin.
Thanks :)
Quote from: Spaceman on 28 Oct, 2022, 10:02
Here's a pic of the timing end of a B25 crankshaft - you can see where the oil seal contacted it. If your crankshaft is only just contacting the seal then that looks to be a problem?
Thanks :)
B25 crank does look longer. I measured mine and used toolmakers blue. The lip of the seal is 1mm in from end of crank shaft. I could remove circlip and pull oil seal out a bit like earlier models?
Without the circlip, the seal will run the risk of being blown out by the oil pressure.
Just to recap: the evidence seems to point to an absence of oil getting to the big-end bearing resulting in no oil being thrown out to coat the cylinder resulting in a seized piston. The evidence of oil returning to the oil tank seems to suggest the pump itself is doing its job.
Unless there is a blocked oil passageway from the pump to behind the crankshaft seal, it would point to the seal not being able to do its job. A 1 mm projection of the crankshaft boss beyond the lip of the seal may not be sufficient.
I've been trying to understand why the boss on the end of B44 crankshaft is shorter than on a B25 - I believe the inner timing covers are essentially the same so that changing to a B44 cover would not solve the problem. It may be down to a difference in design of the crankcase because, at the end of the day, the boss on the B44 crankshaft must project the same amount past the seal as on a B25. The pic shows where the seal interacts with a B44 boss.
Although the problem is looking to be with the crankshaft seal, it would be worth ruling out a problem with the oil passageway within the crankshaft at this stage. To test, you should be able to squirt oil from an oil can down the hole in the end of the crankshaft and see it emerging from around the bottom of the con rod and then running down into the sump. Hopefully, this will show the crankshaft is ok.
Due to the B25 circlip the seal sits deeper in the B25 cover, shown in this cross section view.
Quote from: Spaceman on 28 Oct, 2022, 17:31
Without the circlip, the seal will run the risk of being blown out by the oil pressure.
I wouldn't worry about oil pressure as there isn't much due to the roller big end. As Julian has highlighted, the B25 seal was mounted futher into the case to allow for the circlip, so if it were my engine I'd remove the circlip and oil seal, then make a spacer to go under a new seal that was positioned in the same place as for the B44 case (your inner timing case looks to be for a 1971 OIF model B25). Obviously making sure that there were no witness marks on the new seal when cover bolted up then removed again just to be sure.
It looks as though it was just the B44 that didn't have the circlip fitted - even the later B50 had one. Not sure why BSA would have changed the design of the B44 crankshaft and the inner timing cover compared with the B25 even if the circlip was strictly not needed because of the low oil pressure. Why didn't they just not fit the circlip?
Ironically, I have an inner timing cover sitting on my bench that doesn't have a circlip fitted - it has casting number 70-9409 on it which makes it from a B44. Happy to measure it up if this will help to ensure the seal is re-positioned correctly.
A B44 at startup with cold oil could perhaps have a high oil pressure and thus the circlip is a good thing.
Quote from: JulianS on 28 Oct, 2022, 18:16
Due to the B25 circlip the seal sits deeper in the B25 cover, shown in this cross section view.
Thanks for the information. Now that is interesting :)
Thanks everybody for the information.
I have just been up to see Roger at RTS. He will do the barrel for me and has piston in stock. 8)
He also has the proper inner timing cover for my B44VS :).
I will let everybody know how things turn out... Thanks again.