B44 has seized!

[Spaceman]

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.

[Spaceman]

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.

[JulianS]

Due to the B25 circlip the seal sits deeper in the B25 cover, shown in this cross section view.

[Ian C]

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.

[Spaceman]

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.

[LightningAndStarfire]

A B44 at startup with cold oil could perhaps have a high oil pressure and thus the circlip is a good thing.

[jossbatey]

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 

[jossbatey]

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. 

He also has the proper inner timing cover for my B44VS  .

I will let everybody know how things turn out... Thanks again.