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[jawa-enfield]

Okay, so i have gotten this piston at a workshop with the cylinder.. they want to know how much play the piston should have in the cylinder..
https://accessories.hitchcocksmotorcycl ... rt%20500cc

The piston did not com ewith this info...

[jawa-enfield]

..by 'play'i mean clearance.. what should be the bore diameter in comaprison to the piston?

[Haggis]

You need to give Hitchcocks a call and ask what the clearance for that make of piston should be.
Different types of piston need different clearances.
Forged, cast or wire wound are all different.

[jawa-enfield]

Got reply, that it should be 0,0045 to 0,0050 inch, but that is over 0,10mm's and that's practically worn out?? so maybe a mistake somewhere..
Even my dnepr had 0.08 mm. piston clearance..

[Haggis]

Workshop manual for 500 uce says,
Piston to bore clearance,
New Min. 0.095mm......3.7 thou
New Max. 0.115mm.......4.5 thou
Service Limit. 0.30mm......11 thou.

[jawa-enfield]

Our host tells me the forges omega/accralite piston needs more clearance (so expands more?? and will rattle more)
so guess he knows best..
Because of more play needed.. it is still an improvement.. right? No disaster-cases with these pistons? (i would like the engine to be okay for a while after some heavy investments.

and yes it think it is a lot, but maybe i make the mistake by comparing it with a 650 twin engine (smaller pistons)

[Adrian]

Haggis,

this is for a '94 500 Bullet, not the UCE/EFI. Can't remember whether we're dealing with the original cast-iron cylinder barrel or an iron-linered alloy after-market barrel.

Just a thought, did anyone ever produce nikasil alloy barrels for the old Bullet? I gather these can run successfully with slightly tighter clearances.

A.

[Haggis]

Not had to rebore any of my enfields yet but my 1953 Matchless G3LS with cast iron cylinder was rebored to have 1.5 thou per inch of bore clearance.
This was to suit a modern JP piston.
Bore was 2.7 inches so still around the 5 thou clearance.
Older matchless pistons had a wire wound piston and ran as little as 1 thou per inch of bore.

[Lone Wolf]

Wotcha.

Our host tells me the forges omega/accralite piston needs more clearance (so expands more?? and will rattle more)

I've had an accralite piston in my 570cc Bullet since 2007. It has the most horrendous piston slap - in fact it sounds like a diesel engine . . . . .but it's still running happily despite that. At least with that much clearance, there's little chance of it seizing up.

[Presto]

Any reliable supplier of pistons - especially expensive ones! - will include all vital dimensions (ie piston to bore clearance] with the piston. I know our hosts do. And it's VITAL to get this right - or the piston will be wrecked within the first few miles.

The Omega piston needs a wider clearance than some other types - generally around 5.5 - 6 thou.

(Or has someone said all this before??? )