Engine Rebuild

jschweig · 08-30-2001, 12:54 PM

I am rebuilding the engine on my 86 951. When I pulled the head I noticed some very very slight scratches in cylinders 3 and 4. I am wondering if it is ok to have them honed. I know about the special coating but cannot find any difenitave information on what needs to be done to the cylinder walls before rebuilding. Also what is used to remove carbon deposits in these locations: top lip of cylinders, top of pistons, botton of head, valves. Can the same springs be used? And is there anything out of the usual that should be replaced? I know about water pump, timing belts etc. Thanks in advance. I wouldn't want to damage my baby.

Scott R · Scott R's Garage

Those small scratches are most likely the result of pieces of the lower main breaking down and getting into the cylinder. This can be fixed to some degree, find a skilled engine shop that has done Porsche motors before. The carbon can be both cleaned with chemicals designed to remove and broken off when it's safe to do so. As for the valve springs if in doubt get new ones. You can get OEM or upgrade to titanium if thats your thing.

951carter · 08-30-2001, 06:48 PM

there is not a coating. it is silica in the aluminum. when boring the block the silica has to be polished back out. after this oversized pistons will be necessary.if the scoring is not bad it may be able to be polished out. the necessary products for the procedure can be purchased from sunnen. the springs need to be tested. if they are within spec they can be reused. varsol and/or a wire brush will work fine to remove carbon deposits. good luck.

jschweig · 09-05-2001, 11:06 AM

I can not find anyone who sells Varsol in southern CA. I have tried brake cleaner and soaking then scrubbing with a plastic bristeled brush but this is not working to well. Any other suggestions for removing carbon. How about a fuel injection type cleaner? Thanks.

ae1969 · 09-05-2001, 11:54 AM

....a grinder works great.

On the head....where the head gasket sits ...scotch brite works nice....I like to do it by hand......

on the valves where the deposits are harder a grinder workes great....takes it off ..in no time!

Top of the cylinders as well....grinder works well.... it does not score the aluminum if you get the right grinder... just ask at a engine rebuilding place what they use.

Varsol...you should get that at your paint stores? You should be able to get some. It does loosed the carbon to some extent... but you still have to grind....and boy do they come out shiny....

Grinder could be ...air ...or the end of a power drill.... uhmm even a dremmel.... take your pick....

eimkeith · 09-05-2001, 12:36 PM

that scoring is most likely FOD (foreign object damage) as I was told when I checked out our 951. Most likely some chunks of carbon knocked off a valve, etc. Or possibly the result of leaky injectors, which leads to gas-washing of the oil from the cylinder, and scoring results.

I believe the above scenarios are more likely to be the cause than Main bearings breaking down...

I left the slight scoring alone. My reasoning: forced induction and the Motronics will take care of the slight compression difference, if there was one, and I figured if it really was a problem, I'd get smoke at startup.

Guess what - no smoke. When I get through my baby-it-the-first-200 period, I'll let you know if I can realy detect a difference in running condition or power between that particular car and my personal 951, if you'd like...

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keith
'86 951 redNeckarsulm

eimkeith · 09-05-2001, 12:38 PM

BTW - VARASOL is an EXXON product - go to a fuel oil distributor. They will sell it to you in 5 gallon buckets.

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keith
'86 951 redNeckarsulm

jschweig · 09-05-2001, 12:57 PM

Thanks redNeckarsulm. I had no problem with a smoking engine before the tear down. Just really low compression but it ran like a top. When you did the rebuild what procedure did you use on the cylinder walls? I am going to replace the rings and was wondering if the walls need to be honed? There is also a ridge that is not noticable visually but is noticeable by touch at the top and the bottom of the cylinder where the wall is out of reach of the rings so what needs to be done there? If you can not tell I really want to rebuild my baby but will do anything to avoid buying oversized pistons. I have acess to a machine shop and a good machinist so I can afford any maching work just not the larger pistons unless it just can not be done correctly any other way.

Cake944 · 09-05-2001, 04:28 PM

You could always try carb cleaner or a gun cleaning solution for the carbon. I use rig 44 to clean all of the carbon off of my guns after 500-600 rounds of shooting. (that is sometimes accomplished in just a few days.)