How much the pistons should stick up out of the barrel?

How much the pistons should stick up out of the barrel?
Thanks for your answers.
Ciao
Piero

On a stock Commando engine = ZERO.

Someone haz bin messin wif somefing if they duz....

Rohan said:

On a stock Commando engine = ZERO.

Someone haz bin messin wif somefing if they duz....

Click to expand...

Hi Rohan,
Sorry, but i cannt able to translate!
Ciao
Piero

Both my '72 Combats pistons protrude .050" above barrel top, w/o a base gasket.

Did the factory build the combats without a base gasket ?

Are your pistons stock ?

pierodn said:

Rohan said:

On a stock Commando engine = ZERO.

Someone haz bin messin wif somefing if they duz....

Click to expand...

Hi Rohan,
Sorry, but i cannt able to translate!
Ciao
Piero

Click to expand...

someone has been messing with something, if they (the pistons) do (stick up higher than zero)

I know of no engine where the pistons at TDC are higher than top of the barrel. Always been flush and seldom a few mm lower. If they were higher they could and would smack the cylinder head, especially if oversize after a rebore. Sounds like the con-rods are not original spec or someone has skimmed the top of the barrel. Put a number of cylinder base gaskets below the barrel to lift the barrel up a few mm.

Both my Combats came with smooshed down leaking base gasekets which still allowed both these Combat's 4 pistons to stick up proud of bores with unmeasurable difference between the pistons proudness. i did not measure on dissassemblies just noted pistons proud of barrels but later w/o base gasket did measure .050" out of barrels. Do not know if applies to non Combat Commandos but the fact that Combat pistons do travel past-trhough the head gasket is what makes alu gaskets taboo as alu eventually mooshes into bores to rub on pistons - which in Trixie's case were taboo stress riser oil comma hole pistons that destroyed Trixie Combat engine onlly 3 wks after returning her&me to use again >after 3 yr prior horrific head on rump deer strike @ 70 mph combined speed >after only 3 wk very timid initial use on first accquiring Trixie in Feb 2006 for recovery gap till spring 2009 to be a stupid Commando cycler again.

Engie said:

I know of no engine where the pistons at TDC are higher than top of the barrel. Always been flush and seldom a few mm lower. If they were higher they could and would smack the cylinder head, especially if oversize after a rebore. Sounds like the con-rods are not original spec or someone has skimmed the top of the barrel. Put a number of cylinder base gaskets below the barrel to lift the barrel up a few mm.

Click to expand...

No...do not use multiple gaskets.....your barrels will move around on them....

If you need to raise the top of the barrel the use a steel compression plate or copper base gaskets, or even both in a sandwich.

pierodn said:

How much the pistons should stick up out of the barrel?

Click to expand...

I can't say how much but I recall my aftermarket pistons rising a smidgen above the barrel (stock barrel and rods). After 10,000 miles I haven't had any issues with piston to head contact. -pretty sure I would have noticed after the first crank.

I recall getting .050" above the barrels for 750's.
Stock 850 are below.

Stock 750 piston has a compression height (center of wrist pin to top of piston) of approximately 1.54", and 850 is approximately 1.47", from my measurements of used stock pistons. That's why 750 pistons are higher in cylinder than 850.

Ken

Thanks Ken and Dave.
Is that with a base gasket used in the 750 ?

Perhaps we should ask Piero if this is a 750 or 850.
Presumeably its that flat looking cylinder he showed on another thread...

Rohan said:

Thanks Ken and Dave.
Is that with a base gasket used in the 750 ?

Perhaps we should ask Piero if this is a 750 or 850.
Presumeably its that flat looking cylinder he showed on another thread...

Click to expand...

Hi Rohan,
Mine are 750.
The flat cylinder still don't know why I haven't yet installed but I will let you know: However I have a copper base gasket from JPS and a decompression aluminum gasket from Andover.
This time I asked for another 750 barrells: the pistons (+0,60) to TDC protrude off about 1.25 mm.
Thanks.
Piero