I have removed the cylinder head in order to investigate plug fouling and evidence of an oily RH exhaust silencer and in addition the leakage of oil between the head and barrel. There are no spigots on the barrel or head and the pistons protrude 0.135" (3.43 mm) above the top of the barrel and are flat topped . Are the pistons standard or high compression ?
The pistons are + 0.060" and the bores measure 2.735" dia. Next week I will remove the barrel and measure the bores and pistons more accurately. There is no scoring of the cylinder bores so perhaps a honing of the bores and new piston rings might do the trick. However, that is only if the pistons are deemed to be standard compression as I do not want high compression pistons.
I have not had chance yet to check the valves and valve guides as worn guides might be the culprit.
I would appreciate any advice regarding the piston dimensions as I am not at all sure as to whether they are high compression or not. Also what is the recommended clearance between the piston and bore ?
In fact I would appreciate any advice !
Thanks in advance,
George
Ideal clearance would be…
- Log in to post comments
Cylinder barrel
Just an other thought. As there is very little boss height on the top of the barrel I suppose that a previous owner could have machined the boss off to raise the compression. What is the overall height of a standard 99 barrel ?
George
- Log in to post comments
99 barrels Queries
Hello Now first this is there over bored (99) and 650 Barrels were only made to be bored No more then plus 40 over and the piston to skirt clearance with out rings is no more then 0.003 or 3 thou as standard the original pistons would of been hepilex expanding skirts with the compression ratio of 7.5.1 later on these were rased to 8.5.1 the racing pistons that were domed crowns were 10.5.1 I had at one time a racing Dominator model 99 a 1961 (99SS ) with had a racing clutch and gearbox and special parts made for the internals made By the curtsy of BR Doncaster Locomotive workshops , and your oil leak will be coming from between the cylinder and the push rod tunnels , now have fun yours Anna J
- Log in to post comments
Flat topped pistons
Flat tops on 99 pistons are "standard" not high compression.
- Log in to post comments
Ideal clearance would be around 4-5 thou at the skirt, if the motors history is not known its possible that its not run in . You also need to determine what is the lube system as owners make changes thinking more oil is better.