The BSA A7-A10 Forum

Technical (topic titles must be descriptive) => A7 & A10 Engine => Topic started by: chaterlea25 on 15.07. 2011 23:19

Title: A10 Autopsy!!
Post by: chaterlea25 on 15.07. 2011 23:19
Hi All,
Over the last few days I have found time to dismantle an A10 Super Rocket engine that is destined for a project bike
The engine has been laying around for qiute a while and has had some parts "borrowed" to keep other A10's on the road

The engine has an 1126 alloy head that has "Eddy Dow" type alloy top caps and what appear to be "gold star" valve springs, bottom collars look to be standard SR type, (I will add some head photos later)

The dynamo clamping bolt pin had been sheared off and drilled through again askew  *sad2*
I managed to remove the damaged bits !

The barrels are thick flange type and are on +.020 with very little wear so hopefully will re use after painting
The pistons are 8 or 8.3:1, the pins were reluctand to move even with heat? and there appears to be a ridge inside the circlip grooves, the pins were free to turn in position, probably too loose *sad2*
The cam and followers look fit for further use  *smile*
Ther was a fair amount of "wobble " on both Big ends *eek*
More so on the timing side?? Then I noticed that there are 2 drive side rods fitted (with the oil bleed hole ) ????

I cleaned out the grease from the dyno drive compartment and after removing the dyno drive sprocket I could see that at some time the chain had come off/broken and the case had a welded repair  *sad2*
When I dismantled the timing side the idler pinion would not come out of its bush in the crankcase ????
I think that the welded case and the crankcase were not in line properly and that the idler gear/bush  has worn with a ridge inside the bush ????

A solid phosphor bronze main bush had been fitted, the crank end has a taper of a couple of thou ????
Timing side B/E shells are worn to the copper and tha crank has 5/6 thou wear (on -.020)
Drive side is better only 1-2 thou wear
This makes me suspicious of either the fit of the shells in the rod or that the wrong side rod caused lack of oil pressure??????

The photos of the sludge trap plugs speak for themselves  *sad2*

The previous owner had used what I think was white bathroom sealer everywhere  ???? ???? *eek* *eek*
Happily some petrol dissolves this easily

The first repair job I tackled was the crankcase threads on the drive side, its common t ofind these damaged/stripped
so I fit solid "top hat" inserts, these cant move inwards which can happen if a helecoil insert is used
The inserting tool expands the inner end to make sure they stay in place

I hope the photos are informative, I have loads more!!
I will need replacement inner and outer timing cases  *sad2*
I will put a wanted thread up

John O R

Title: Re: A10 Autopsy!!
Post by: chaterlea25 on 15.07. 2011 23:25
second lot of pics
Title: Re: A10 Autopsy!!
Post by: chaterlea25 on 15.07. 2011 23:27
3rd lot
Title: Re: A10 Autopsy!!
Post by: chaterlea25 on 15.07. 2011 23:30
thread repair inserts

John O R
Title: Re: A10 Autopsy!!
Post by: muskrat on 16.07. 2011 05:37
Good to see it has been rescued, John.
At least you can see they cleaned the sludge trap out once or twice.
Title: Re: A10 Autopsy!!
Post by: bsa-bill on 16.07. 2011 08:26
Plenty keep you occupied John, as they say it's seems to have a bit of history, idler pinion has been lightened at some time
Title: Re: A10 Autopsy!!
Post by: chaterlea25 on 16.07. 2011 15:06
Hi Bill and Musky,
Yes, there are several "non standard" aspects to this engine,
The rockers have been lightened and polished,
Gold star valve springs and alloy caps
Drilled idler and mag pinion
Taylor Dow finned  rocker covers and oil feed
A good few drilled nuts for lockwiring, so it must have been used in anger at some time  ????

John O R
Title: Re: A10 Autopsy!!
Post by: wilko on 17.07. 2011 20:35
I'd throw the alloy valve caps if i were you. I'd be paranoid about the valve colletts pulling through.