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aerochip aerochip is offline
Registered User
Join Date: Jul 2012
Location: Park City, UT
Posts: 81
One Dead Cylinder

I have an '85 930 that I got about a year ago with 68k miles. This car is all stock and appears that it has never had the motor out (very limited records came with it). The care was in great condition, but had been driven very little over the past 10 years or so. I had a PPI done that showed it was pretty solid, but did have some gremlins that the previous owner(s) probably didn't care about fixing since they only drove an average of 800 miles/year. I drove it all summer and fall and did a bunch of DIY projects to get things sorted and reliable (CV boots, switches, shift linkage bushings, removed aftermarket alarm, etc). By the end of the summer, after a couple thousand miles of reliable and enthusiastic driving, it was leaving a few decent size puddles of oil on the garage floor. I also noticed that it was smoking more on start up and starting to consume more oil than was landing on the garage floor.

So, last fall, I decided to take it down to my buddy's house for winter storage and to tinker on it with him (he is an accomplished mechanic on all sorts of equipment from big rigs to now being a partner in a motorcycle shop).

We decided to pull the motor and do a full re-seal, replace the oil return tubes as they were leaking heavily, and replace lots of other suspect seals. Along the way, we decided to do a leak-down check and this is where the fun begins:

First leak down test
#1 = 18% Acceptable
#2 = 98% BAD - leaking through exhaust.
#3 = 14% Acceptable
#4 = 15% Acceptable
#5 = 19% Acceptable
#6 = 18% Acceptable

We then adjusted all valves. All were pretty close. Two intake and two exhaust valves loose and one exhaust valve tight.

Re-tested #2 and improved marginally to 95%. Then put a little oil in the cylinder and tested again. This time improved to 90%. Still not acceptable, and still leaking heavily through the exhaust. One thing that may have contributed to this issue is that the motor got pretty hot a few times during low speed driving last summer due to crimped/crushed oil lines to the front oil cooler - could this have damaged the exhaust valve or seat? I'm assuming the replacement/repair of the front oil cooler lines will help thing immensely.

Given that this test was performed on a cold engine, I would say all, but cylinder #2, are in good working order. This leaves the question of, do you only make repair to that cylinder? Or all 1-3 cylinders. Then, do you leave the other side alone?

I really like this as a stock car and expect to drive up to 5k miles/year. Any insight from the Pelican gurus on how far into this you would go?

Old 05-06-2013, 05:38 PM
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