Flyer95

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Hello,
I am in the process of putting new hard chrome on the liner of one of my ABC engines for which parts are not available.

I know that the top of the liner should be slightly smaller than the piston, but how much? Does anyone knows what the tolerances should be?

speedracer1129

i don't know the tolerances, but in car engines, i usually notice that the top of the sleeve is about 4mm smaller than the bottom of the sleeve in inner diameter. hope this helps

William Robison

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Speed:

You have your decimal point wrong. 4 mm is more than 1/8" - you might mean 0.04 mm, that's a little more than 0.0015"

Bill.

BillS

It is not a good answer but most of the engine tuners I know would prefer the chrome to be piston size and then hand lap to fit.

You might want carry your micrometers to the LHS and measure a new piston sleeve set. You could also check the taper.

Bill

Flyer95

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I would like to have a good pinch at TDC like a new ABC engine. Any ideas?

If the liner is 0,01mm smaller than the piston would it be too much?

w8ye

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.04mm is more like they are from the factory

enjoy,

Jim

William Robison

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Flyer95:

The fit at the top of the bore should be zero clearance. Any interference fit would force you to heat the cylinder just to get the engine to turn through.

Also, if you have gauges of sufficient accuracy you will find the piston is not a true cylinder - it's more a barrel shape. very slightly larger diameter at the center than the top and bottom while the cylinder sleeve bore is a straight taper.

Hope this is some help.

Bill.

Flyer95

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Thanks for all the help.

Flyer95

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Hi Guys,
A few more questions

Is the brass in the liner for ABC engines just brass? or a "special" brass alloy?
How thick do you think the hard chrome plating should be? for long life and good expanding capabilities. Any suggestions? Thanks

Motorboy

Yes, just brass.. Chroming the liner you need special tool as i show in picure.
Thickness in chrome shall be 0.05-0.08 mm and lap to mirrorlike surface then thickness will be 0.02-0.03 mm after the sleeve are lapped.

When you are lapping the sleeve, you need a ready made piston to test taper in sleeve between lapping. In bottom are piston loose and before 1-1.5 mm to top the piston will be tight. It must be tapered to keep compression when the engine are cold.

Very important! Wash parts in petrol or kerosene before piston are entered to sleeve.

Jens Eirik

Flyer95

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Thanks Jens, What a great help you are. That explanation makes everything much easier.