'88 3.2 #5 cylinder failing

[Chris Lovell]

Hello all,
My '88 3.2 has good compression and leak down on all cylinders except #5. #5 has bad compression (~100). #5 plug will clog and fail if the engine is not run high. Anyway, at 120k miles and 37 years, I am likely a candidate for a rebuild.
Q: Does it make sense to restore one cylinder only? Or, once out, rebuild the whole engine? And while I'm asking, is there any sense in swapping in a rebuilt engine versus rebuild this one?
Thanks for thoughts. (or please steer me to where this topic has been covered previously)
Chris

[Porsche 935]

My plugs all look great even at 218000 miles. Is it oil fouled or gas fouled? Maybe you have a stuck injector?

[911MANN]

My (unprofessional) recommendations below. Hopefully, true experts will chime in. But at this age/mileage, you will want to do something like the following:

1. Bring it to a trusted 911 mechanic to let him spend some time with it and offer his thoughts.
2. Top-End Refresh: Drop the engine, pull the heads and determine cause of bad compression in
No.5. You will want new valve guides and rings after going this far. And new head studs also. Many
choices re: head studs, but I like Supertec.
3. New clutch and flywheel.
4. Attend to the Triangle of Death and any other (hopefully minor) things that are smart to
replace at this stage.

This would be bare minimum for me, but it should allow another 120K miles if fortunate.

[Chris Lovell]

Originally Posted by Porsche 935

My plugs all look great even at 218000 miles. Is it oil fouled or gas fouled? Maybe you have a stuck injector?

Definitely oil fouled. I guess that means rings. But that's just my take.
As 911Mann notes, this is probably the time for a top end, and if rings, bottom too.
All thoughts are welcome. Thank you.

[917_Langheck]

You need to do a leak down test to determine whether it's blowby at the rings, exhaust valve, or intake valve leak. Then check the condition of the spark in #5. Is #5 spark plug the same type and heat range as the other? Is it in good condition apart from being fouled? What's your wire set like? How much oil are you using per 1000 mi?,

[E Sully]

Could be gummed up rings or poor sealing valves from carbon build up.
I bought a used '86 3.2. It obviously had oil getting into the cylinder issues.




My searches showed they were known for valve guide wear. The Nikasil cylinders still showed good cross hatching. I redid the heads with new valve guides and exhaust valves, along with having the cylinders honed and new rings. After break in it had great leak down and compression numbers. Great running with no significant oil use.