what rings for 3.9V8?

[tumchiehead]

Having done a compression test last week and got dismal readings( all about 90psi), I decided to strip down the engine and check the internals. Apart from the piston crowns and head valves being heavily carboned, everything else looks brand new. Checked the top compression ring gaps and they are all between 25 and 27 thou, 2nd ring gaps all between 21 and 25 thou, seems a bit high to me, LR manual says max is 22 thou.
I dont have a Bore micrometer to check the liners, but, there is no lip on the bores, the crosshatching is still clearly evident and I verniered the cylinders at the top to 94mm blob on. Do I just fit the standard size rings?
the rings presently fitted don't look like chromed to me!!
any help much appreciated
ps whats the best way to get carbon crud of the piston crowns
cheers
Tumchiehead

[katanaman]

sounds to me like a new set of standard rings would be ok and I would advise a session lapping the valves in. This is probably where you were loosing most of your compression anyway. You must have your pistons out so a dose of oven cleaner is the stuff to use to get the carbon off. No idea where you are in Edinburgh but I have bore mic's and could do a measure up for you if you want although it sounds like your bores are of. Couldn't do it or next week though.

[tumchiehead]

Thanks for the advice, I don't think the bores need checked, they look brand new. I think the engine's been refurbished although I have no idea of the history, but the camshaft has blue paint on it and the cyl heads also have blue paint circles on them. The tappets, pushrods and the rockers are all pristine and unblemished. The engine was in the car when I got it(Sylva Striker kitcar) Previous owner used it for hillclimbs etc, so, I guess if it was refurbished, it wouldn't have done many miles since.
I'm in Corstorphine just off Drumbrae south, Thanks again for the advice, I've never stripped an engine in my life so it's all a bit new to me.
regards
Tumchiehead

[jefferybond]

ps whats the best way to get carbon crud of the piston crowns

Once the worst is off with a blunt scraper, i found that WD40 combined with a foam scouring pad worked very well. Also good for getting the carbon off from the tops of the bores without damaging them.

Jeff