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914World.com _ 914World Garage _ To Lap or Not To Lap

Posted by: Headrage Nov 6 2004, 06:49 PM

Just got my heads back from Rimco and bought a new set of Mahle p/c's. Do the cylinders still need to be lapped?

Posted by: Joe Sharp Old Nov 6 2004, 06:52 PM

Allan: I don't do it. Do you have your cast off yet?
Joe

Posted by: Headrage Nov 6 2004, 06:54 PM

Yep, I made then take it off after 2 weeks because it started to smell like rotting meat. I think it got wet from being out in the rain. Once they got it off I talked the doctor into putting me in a cam walker that I can take off to shower and sleep.

Posted by: skline Nov 6 2004, 07:38 PM

Your choices are simple, install using the factory head gasket or lap them in. I would lap them in to be sure of a good seal. If you dont, any kind of imperfection could turn to a burned head or cylinder, most likely, the head.

Posted by: newdeal2 Nov 6 2004, 07:49 PM

This is how I lapped mine [per a Porsche mechanic]

Apply valve grinding compound to the end of the cylinder, place it into the head and with even pressure rotate the cylinder back and forth a few times. Make sure you wash the residue of of the surfaces when done and keep each lapped cylinder in the same location on the head.

DO NOT install the gaskets , they will leak.

Posted by: newdeal2 Nov 6 2004, 07:52 PM

Oh, by the way....do install the metal gaskets on the case side and use a case sealer.

Posted by: Joe Ricard Nov 6 2004, 08:01 PM

Lapped the used cylinders to used heads 1.7L engine. Ran living piss out of it hours of Freeway travel near 4000 RPM and then Autocross it banging the rev limiter. Got it hot ran t more. When I pulled the motor apart the heads showed evidence of a perfect seal.

LAP THEM it is easy and well worth it. I also did not use a head gasket or base shim. The compression ratio was just a little higher

Posted by: skline Nov 6 2004, 08:05 PM

I dont use a base gasket either but did put some sealer on it. Otherwise, it will leak eventually.

Posted by: Joe Ricard Nov 6 2004, 08:14 PM

All depends on the deck hieght. and the compression ratio you desire. Maybe you could put some stupid big ass copper rings inbetween the head and cylinder, Oh and make sure the ring is an 1/8 th inch smaller the the head diameter.

Oh sorry that is what the P.O. did to the project engine. Can you imagine the leaky head this thing had. one side of the ring was completely burnt.

Posted by: newdeal2 Nov 6 2004, 08:28 PM

I used the base gasket w/sealer per Jake's video. I didn't think that what, .006 or so of gasket would add much compression and I am using flat top pistons and a Webcam so life will be good...if I didn't screw anything up internally that is

Posted by: Elliot Cannon Nov 6 2004, 09:18 PM

Put the cylinder in the head and rotate it back and forth for 2 minutes. Turn it 90 degrees and rotate it for 2 more minutes turn another 90 degrees etc. etc. Very important to get ALL the valve grinding compound cleaned off the cylinder and head surfaces. This method takes awhile and is very tedious but insures a good seal.
Cheers, Elliot

Posted by: Headrage Nov 6 2004, 09:40 PM

Something that I should probably know but don't is, does it matter which cylinder goes where. They all look the same to me.

Posted by: newdeal2 Nov 6 2004, 09:46 PM

They all have a flat side [finned area] that faces in and the piston arrow should point towards the flywheel. Do the number 4 cylinder first so you can get the circlips in and work your way around.

Posted by: Headrage Nov 6 2004, 09:55 PM

So it dosn't matter which cylinder goes where?

Posted by: newdeal2 Nov 6 2004, 10:06 PM

No. But keep the piston with it's cylinder. By the way...follow the last suggestion on lapping. I didn't take that much time but it's probably better to go the whole 360 as he described.

Posted by: Headrage Nov 6 2004, 11:50 PM

Thanks guys. You have been really helpful. Now as soon as the bearings get here it's time to put it all together.