Made it, but only just.

[bossy]

OK; have returned under own power from Alpine tour, but it was a close run thing, the issue being Vibration.
When I put the bike together earlier this year I had Mark balance the crank, rod, piston etc and it was smoother than any other unit single I have ridden. As the last trip progressed it went from average to bad to damm near unridable. In any other circumstances I would have given up rather than risk further damage.
So when I got home this afternoon I lifted the Head and sure enough there is major piston/bore wear.

The piston is a GPM slipper, fitted new in March to a Cylinder bored by the best in the business, done about 2000 miles. However to be fair I have been running without an Air filter cus I just didn't get around to fitting one - not so easy using my B50 frame/B44 motor/Mikuni setup.

Whilst I will now sort out a filter, the question is how big a factor was its absence? Should I risk another GPM piston? What else is available in 80mm that is not superhigh compression?

Your thoughts would be appriciated...............

[Mark Cook]

Amazing Paul that it lasted that long. Though from experiance the BSA bores ware out very fast in racing conditions. This is why I developed the alloy liner/plated bore setup. If you were tempted down this route take it to 82mm, I'm going to do this on my Ian Hingley replica. Again, amazing you made it.

Mark

[HPbyStan]

My dad put 70,000 street miles on his '58 Gold Star with no air filter. If you CAN fit a filter, do it. If you can't, 70,000 miles ain't bad.

[bossy]

Amazing Paul that it lasted that long. Though from experiance the BSA bores ware out very fast in racing conditions. This is why I developed the alloy liner/plated bore setup. If you were tempted down this route take it to 82mm, I'm going to do this on my Ian Hingley replica. Again, amazing you made it.

Mark

I guess its an option, maybe you could PM cost and turnaround time? Thanks.

[Mark Cook]

PM'd Paul.

Just another thought, If the sludge trap is blocked that will bugger the bore too. The big seems to last quite a while with no oil

Mark

[bossy]

Thanks, I'll check. But as it used 2 litres of oil in the last 1000 miles, was pumping plenty back to the tank and has a thick layer of oil residue on top of the piston I'm guessing its OK.

With the benifit of hindsight riding through a sandstorm in Dunkirk without an air filter wasn't the brightist thing I have ever done, but it surely isn't the stupidist either!

[bossy]

It doesn't take much! There is no step at the top of the bore and the honing marks are still just about visable, the piston looks almost as new too. But I can now get a .009" feeler gauge between piston and bore. It looks as if the bore may have distorted a bit? Maybe +0.060 is a bit marginal on a 441 liner?
Anyways whilst this explains oil consumption of about 1 litre/500 miles, it doesn't provide an answer to the vibration issue. One broken rear engine mount may do, but was that cause or effect? Any ideas on what else to check?

[Ian Hingley]

Hi bossy

Welcome home! I'm jealous. Of your road trip, not of your worn out engine!

Yes, +060 is very marginal on a B44 liner. BSA only ever recommended +040 and I now know why.

This is what triggered the rebuild of my otherwise well running motor last November. And we all know how well that went / is going!

I'll repeat the details for you later.

Cheers

[beat]

hi bossy,
faults on liners are usualy " to feel " ore to see, faults on piston ore piston rings are much more difficult to realise.
I think, a " good " piston is a good investment to a engine, and as the standard " pice of aluminium " and the GPM are from yesterday, I would go in to this direction for the todays travic .....
beat

[JeffB]

I totally agree to Beat's statement about using "good" pistons.
Pistons should always be the best available. This really makes a big difference in durability and overall performance I would say. The problem is often that it is very easy to get "economical" priced pistons from one of the known piston suppliers, but when it comes to real quality forged pistons, it is not as easy to find suitable suppliers and of course they are more expensive too.
But they are worth every cent or penny. I personally got the pistons for my A65 (the B50 is still fine with what the PO put in) from Helmut Wahl in Germany. http://www.wahlspezialkolben.de They allowed a much smaller running clearance than the previously used Hepolites and I never had problems despite hard use.

For what it's worth,
Jeff

[beat]

go with you jeff.
the piston in my B50 is worth each cent, and as it has done somewhere by 3 000 Kms now, it realy seams as the rings have bedded in now nicely!
the engine never had such a low blow by in its al livetime bevore !!!
this is shurely also a result of a perfect rebore work wich was done by Mark Cook .

so we can say, : it is nice to have the choice of something lower in costs wich keeps the bike running, - and something modern wich is more expensive but made for the todays travic.

for myself - I would not beleve the difference if somebody was telling me this , now, I made the experiance on my own bike, - I must say : surprising
beat

[bossy]

I have to be fair and say that I could not detect any fault with the GPM piston, it is sitill as good as new. My problem was wear to the bore. It may be that lack of air filter was the problem, but I suspect that a B44 liner is just not thick enough to take a +0.060 bore. BSA supplied +0.060 pistons for all other models but not B44, there was probably a reason. Also if you look closely at the pic I posted you can see an area which has not been wiped by the rings - it was round when it was bored but not now. Liner distortion?

I have used GPM pistons in both 2 and 3 cylinder Laverdas without any problems and whilst I wouldn't specify one for a race engine they have always been fine for the sedate way in which I ride.

Anyways the bike is back together now with a different barrell and a new +0.040 GPM slug. I'll let you know how I get on.

[beat]

hi bossy,
nice to here yours is back in place, - wonder what you can tell us now and in 2 ore 3 k Kilometers abouth the piston / bore .
I just can not se the wearing coming from the airfilter, - four strokes are non sensitive ad this point I guess....?
good rides,
beat

[b50root]

I just can not se the wearing coming from the airfilter, -

I agree with Beat. I have never in my 25 years with B50 used a airfilter.

Rickard