Author Topic: pistons??  (Read 1019 times)

lee78

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pistons??
« on: 08:14, Wed 01 October 2008 »
after stripping my engine down and finding 1 of the conrods pretty much fooked i ordered another from cgb with the piston stil attached only to notice the piston was different from the others of mine, after cleaning the top on 1 of my pistons it appears that the crowns on top have been milled down to a flat finish as you can see and feel a slight lip on the edge of where it should be, i was told it was probably done to lower the compression is this good or bad or are there any other reasons why this might have been done as i am about to start rebuilding the engine? i was told i could flatten the crown on the piston i just brought to match the others, is this a good idea or should start to consider replacing the other pistons? would be grateful of any info

5teve L

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« Reply #1 on: 08:56, Wed 01 October 2008 »
Up to you mate, yes you could prob get the piston crown milled down, you'd have to take one of the other pistons out to measure exactly how much has been removed though.
Or bite the bullet & buy some new pistons & liners, but then you'll need to find an engineering place to fit the rods to the pistons as it's not easy at all!!

James5

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« Reply #2 on: 11:50, Wed 01 October 2008 »
Probably been milled down to lower the compression ratio this could have been done for a number of reasons, head has been over skimmed, done to run lower compression to prevent det, etc...

lee78

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« Reply #3 on: 12:45, Wed 01 October 2008 »
thanks people, ive ruled out the head being over skimmed already as ive took the head to be skimmed  along with the crank to be reground and the guy said it didnt look like the head hadnt been skimmed at all but now that it will be could i benefit from the pistons being milled down as im also going to be replacing the fly wheel with the lightened and balanced 1 along with the piper 285 kam and also a bigger turbo at some point to up the power, also i noticed that some of the stem seals were missing when i stripped the head down, im thinking for the money i might as well replace them but on the other hand i dont fancy 1 lifting and breaking and damaging a newly built engine as i read in an earlier post somewhere on here that 1 had ended up damaging the kam, sorry for the long posts but im after as much info as i can get as im not as clued up on this engine rebuilding as probably most here but im learning

James5

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« Reply #4 on: 13:36, Wed 01 October 2008 »
Quote from: "lee78"
thanks people, ive ruled out the head being over skimmed already as ive took the head to be skimmed  along with the crank to be reground and the guy said it didnt look like the head hadnt been skimmed at all but now that it will be could i benefit from the pistons being milled down as im also going to be replacing the fly wheel with the lightened and balanced 1 along with the piper 285 kam and also a bigger turbo at some point to up the power, also i noticed that some of the stem seals were missing when i stripped the head down, im thinking for the money i might as well replace them but on the other hand i dont fancy 1 lifting and breaking and damaging a newly built engine as i read in an earlier post somewhere on here that 1 had ended up damaging the kam, sorry for the long posts but im after as much info as i can get as im not as clued up on this engine rebuilding as probably most here but im learning


If your replacing the cam with the 285 don't forget you will need different valve springs and a vernier pulley to time it in correctly. If your going for that particular cam when ti comes to a turbo a full T25 is known to work very well ask GTTboy. Never heard of the vavle stem seals damaging a cam but I suppose it could happen, (Personally I would still replace) as it's all apart.

lee78

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« Reply #5 on: 14:34, Wed 01 October 2008 »
cheers matey, i will be ordering the full kam kit sometime soon, i think there maybe uprated valve springs already on as i read on here the originals were red and mine are not but a new set wont hurt anyway to be sure, ive also got a forge single port actuator on the standard turbo but im unsure of the min or max psi so i was thinking of replacing the spring with with a forge t2 14-18 psi spring or should i go for a lower 1, obviously i wont be tryin to run 18 psi til i gt my fmic and bigger turbo and carb jetted but im assuming this will be ok for minimum boost as you can run 14 psi max on a standard setup right?

Ash-Lee

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« Reply #6 on: 17:44, Wed 01 October 2008 »
My valve stem seals keep lifting and i haven't had any problems yet, just the odd puff of smoke on a hot start.

5teve L

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« Reply #7 on: 21:21, Wed 01 October 2008 »
Half of mine had dissapeared when i looked at it..