Ariel Owners Motorcycle Club

Glad we got around to testing for leakage in the bench. You don't need much pressure Say .5 bar or 7 lbs. Squirt some DWF to show the leaks Even a porous casting will muck up 2 strokes. Nev

Ta. Nev!

Hello Clive.

Glad you’re making progress in the hunt for your problem.
If you have some excess crank run-out, you’ll need to rotate the engine whilst under pressure to see if there is any additional pressure drop as it turns?

When I did the same test, not because I had an engine problem but out of curiosity and for a reference level the future, I DID find a significant leak on the primary side seal. Under magnification I found a sliver of seal had been shaved off the seal lip, presumably during one of my dry assembly routines and obviously caused by the razor sharp edge to the crank journal when I must not have used the protective sleeve.
I tested again with the new seal and it held pressure much better, with the pressure only leaking away slowly, which I assume is normal. Disappointingly, despite the obvious leak, the repair made no difference whatsoever to how the engine behaved, which is strange considering much advice suggests that even a porous case can be devastating.

When you get to doing the test again, I pressurised to 0.6 bar and I have the figures for the rate of leak-down for comparison if that would help you.

Thanks, Ivor.

I have been out of action for a while but have, today, resumed work on the job. Here's a brief summary...

Having pressurised the crankcases, I discovered significant leakage from the collar located on the RH mainshaft. (Perversely, the crankcase seal runs on its OD, but there is no seal for the fit between its ID and the mainshaft - who's idea was that)? I also noted some minor leakage between the alternator rotor securing bolt and its thread in the mainshaft.. To resolve the leaks, I sealed the collar with a low-strength Loctite and the thread on the alternator bolt with PTFE tape. I then re-pressurised the cases and noted the leaks were no longer visible. I noted, too that the pressure, in the cases, fell away very slowly. Eureka! (maybe) -let's put it back together and see...

I must say, I reassembled the engine without great expectations as I couldn't imagine the leaks I discovered would have had such a profound effect on engine function.

Happily, I was wrong - it now runs as expected! I've only run it up in the workshop but it'll run from tick-over up through the the throttle-range, very nicely. I obviously need to get it out on the road for a properr assessment but the difference between its original state and how it runs now is truly dramatic! Two-strokes, eh!

Thanks to all who have contributed!