Hitchcocks Forum

Okay..
Newly overhauled engine.
Also the valve guides..
And a omega/accrlaite piston with a build-in clearance of 0,07 inch..
In the metric system it is even more scary; 0,11mm!

Normalyy that's 'worn out'?
Anyway, after about 1200km's running in i had to fill up the oil 2 times with 0,5L..

And yes, i do not understand and it worries me a bit.

Has anyone corresponding experience with this piston?

O.11 mm is 4 thou, (0.004) which would be in the ballpark for a new piston.
If Omega are asking for 0.007 (7 thou) = 0.177 mm it does appear quite a large clearance but it all depends on the piston expansion qualities. Omega should know what their producs require.

If my 350 bullet only used a pint every 500-ish miles, I'd be delighted.

Piston to bore clearence straight from the piston instructions : 0.135mm to 0.145mm
(0.0053” to 0.0057”)

I ran .005" on the Accrillite in Cast barrel 612 for over 65k km,negligible oil used between oil changes,meaning no oil
needed to be added.32mm Amal will keep them cool running.

Hmm
i'm going to monitor the oil use now..
but would be something to swap the piston just for this?

I can remember the instructions read 0,007 inch?
Fitting the piston wa easy, and you could move the piston sideways in the barrel?

Just a thought, going back quite a few years. when we were running Accralite pistons in our 500 racer on + 0.020" size, I had to replace a piston quickly before a race meeting and ordered one and fitted it as soon as it arrived. At the race meeting, the bike performed fairly well [surprisingly], but rattled, smoked and spewed oil from the breather. Back at home, I stripped the top end again to check and I found a standard bore size piston in the oversize bore - A standard piston had somehow found its way into a box marked +0.020"!
Worth a check?

I seem to recall Omega pistons for Velocette Venoms required .0045" clearance.And the original pistons .004".
And i do recall a friends RE Bullet lightning he fitted with an Accrillite at.0065" and Alloy barrel and it sounded
terrible whenever he took off down the road,the rattle was very noticeable.

Then i should dismantle the engine again..
No very noticeble rattle though..

BTW, is it possible to remove the engine with the primary case attached?
For as the engine has to be removed for taking of the barrel..

But still, do not understand...
Valve guides new, new piston, drinks a lot of oil...