If compression test comes out OK, any reason to rip it open? (Page 1/2)
Kameirocco DEC 26, 05:10 PM
kind of an odd question, so stick with me.

1986 Iron Duke with 180,000 miles
- been sitting since 2001, but does start and run, but does run a bit rough (vaccum lines are shot, looks to be the original fuel filter, etc)

I've been down with pneumonia for the last few weeks and haven't been able to do anything with my project in the garage, so my brain has been spinning with some stuff to do and random planning....

I've been looking at getting the proper micrometers and bore gauges to measure the cylinders as i'm planning to drop the engine to replace the motor mounts and chassis mounts... as well as have easier access to replace different gaskets and clean the ever loving hell out of it as it leaks oil from a few different spots (bought the full gasket set as well as head bolts just incase... they were cheap anyways)

but thought backward and realized there is probably no point if the compression test comes out good (this is due to come in the next few weeks as i get energy back)
As long as the numbers aren't terrible and are fairly close together... guessing there is no point to cracking it open.
However, if the numbers are fairly off or are REALLY low, i could at least pull the head and take a look.

Does that sound like an OK plan? or with a motor with that high of milage just due for a basic refresh anyways?
IMSA GT DEC 26, 06:00 PM
Run a compression test first and hope for 130psi. Anything below 100 may indicate an issue.
Riney DEC 26, 06:54 PM
I had about 130,000 miles on my 2.5 and the fiber timing gear went out. I was only going to replace that part but decided if I was going to the effort of dropping the engine to do a complete rebuild. Good thing when i pulled the head i found the head gasket was starting to leak coolant into cylinders 2 and 3. Be prepared as one of the middle head bolts broke on mine while removing and it was a pain to get the head off. It was rusted in the head.
My machine shop advised against using most of the gaskets from the complete gasket set and recommended using Silicone sealant because that is the way the factory put the engine together and how GM designed it. I went with Ultra Gray, I also installed the Fel-pro PermaDryPlus molded valve cover gasket based off of recommendations on this forum. If you are pulling the engine i would recommend Front and rear seals. Check to see if it has the fiber cam gear and if it still does replace it with the aluminum and steel replacement set along with replacing the lifters. New lifters will quite the engine down because with 180,000 miles I would bet they are sticking, mine were stuck.

So yes, i would recommend checking the compression, if compression is good still pull the head, possibly re work it, at a minimum put new valve seals in it. With the head off you can make the determination if you want to touch the pistons, if the cylinder walls look good, just leave them alone and refresh the rest. In my case I replaced everything, Bored out 0.30, but i have owned the car for 37 years and don't plan on parting with it. My goal is as good as new.

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Riney

Vintage-Nut DEC 27, 08:52 AM
1986 Iron Duke with 180,000 miles

As IMSA GT said:

quote
Run a compression test first and hope for 130psi. Anything below 100 may indicate an issue.



In my experience, a good, maintained engine with high mileage normally have cylinder head issues than piston rings problems.

Healthy Compression: All cylinders should have similar readings, usually within 10-15 PSI of each other
Low Compression in One Cylinder: leaky valve or blown head gasket
Low Compression Across Multiple Cylinders: leaky valves and/or worn piston rings

Run the test and to me, plan to rebuild the head...

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Original Owner of a Silver '88 GT
Under 'Production Refurbishment' @ 136k Miles

cliffw DEC 27, 10:51 AM
Compression Test – How To Do It, Dry Or Wet – Review The Results

For the best diagnostics do it dry and wet.

I would do all four cylinders dry first, then wet, instead of a dry then wet test back to back, on each cylinder.

The article mentions a tablespoon of of oil for the wet test. Using an actual tablespoon will make you look mentally challenged. Use this.



hand held trigger pulled.
82-T/A [At Work] DEC 27, 02:02 PM
Well... rebuilding an engine is a whole process of course... but the reward for getting it done properly is having something that runs really well.

I have a hard time doing thing partially. I restored an entire Porsche 944 once and all I intended to do was replace the windshield wipers.


I personally think that if you're going to go through the hassle of removing the engine cradle, you might as well go through the entire motor. Even if the compression is good... there's still significant wear on the motor after all these years. Parts for rebuilding the motor are STILL affordable and still available. I've been buying and fixing Fieros since I got my first in 1996... and I'd have to say that the availability of parts has been declining steadily. My daughter just rebuilt her Iron Duke engine, and MOST of the parts we purchased were closeouts... meaning that they were New Old Stock for replacement parts (American-made stuff). That's all still available... but not for long.
cliffw DEC 27, 04:29 PM

quote
Originally posted by 82-T/A [At Work]:
I have a hard time doing thing partially. I restored an entire Porsche 944 once and all I intended to do was replace the windshield wipers.



Da umm. I should have went to your comedy tour when you were in the area.
richard in nc DEC 27, 06:35 PM

quote
Originally posted by 82-T/A [At Work]:

Well... rebuilding an engine is a whole process of course... but the reward for getting it done properly is having something that runs really well.

I have a hard time doing thing partially. I restored an entire Porsche 944 once and all I intended to do was replace the windshield wipers.


I personally think that if you're going to go through the hassle of removing the engine cradle, you might as well go through the entire motor. Even if the compression is good... there's still significant wear on the motor after all these years. Parts for rebuilding the motor are STILL affordable and still available. I've been buying and fixing Fieros since I got my first in 1996... and I'd have to say that the availability of parts has been declining steadily. My daughter just rebuilt her Iron Duke engine, and MOST of the parts we purchased were closeouts... meaning that they were New Old Stock for replacement parts (American-made stuff). That's all still available... but not for long.



lucky for us 2.5s are in zillions of s10s so hopefully the parts will be available.
Notorio DEC 29, 12:20 AM
As long as you are doing the Compression test, why not also do a Leak-down test? This gives you additional vital information w/o much additional effort. Turned out to be a critical test for me.
cliffw DEC 29, 10:11 AM

quote
Originally posted by Notorio:
As long as you are doing the Compression test, why not also do a Leak-down test? This gives you additional vital information w/o much additional effort. Turned out to be a critical test for me.



I have heard of that. That is where you leave the compression gauge still attached to the cylinder it was reading for a continued time. I think.

Excellent suggestion Notorio. It should be required in every compression test.