[redsly]

I just did a compression test with a screw in compression gauge I bought earlier and I'm not sure about the results...

Here are my results and I would love some feedback on what you guys think and/or any help/guidance you can give me! :helpsmilie:

Ok, first off I know I should run the engine to warm it but I can't at this moment as I have the ignition module and wiring all ripped out. No module, wires, cap/rotor, harnesses (making new ones, so they're not together), etc...

So I decided to run the test on a cold engine and took out all spark plugs.
Testing order was cylinders 5,6,7,8,4,3,2,1. I just started wherever I was standing and I think the more cranking (friction causing heat) may have caused higher results on the latter cylinders tested.

Results (in numerical order of cylinder number):
1. 160, 165 psi
2. 162, 162 psi
3. 172, 175 psi
4. 150, 155 psi
5. 155, 156 psi
6. 130, 135 psi
7. 130, 150 psi (I think the first test wasn't sealed well due to getting my hands in there)
8. 100, 115 psi (I think the first test wasn't sealed well due to getting my hands in there)

:im confused:
I'm not sure on original specs of what psi they should be at, but from what I had found through searching is that some of these cylinders are high which shows signs of carbon build up (ALL spark plugs had that). This still seems like a low reading though. Strange thing is how cylinders 6 and 8 are so much lower, but since they aren't adjacent to one another so it doesn't seem like a head gasket issue. Either way 8 is screwed I guess haha. :doh:

I know I should try putting in a teaspoon of SAE 30 in each cylinder since they vary so much, to check the rings, but since I couldn't heat the engine first I don't want to do that yet. I don't know, maybe I'll do that tomorrow.

Little engine history: Bought in early '96 with 40k original miles for my first Mustang. Came with a complete new gasket set installed. The guy I bought it from had a Mustang shop so I never looked into it... Damn trust... Sat covered under my deck for three years before I snapped the crank in my '85 and decided to put it in this car. Number three cylinder had a noisy rocker, I took an old one and ground it down so it didn't slap, just until I ran the engine for a while to loosen parts and put the original back in after with a new lifter & rod and it was fine. Had plenty of power and started half a crank all the time, but excessive fuel consumption (figured due to the carb). Its been sitting for ten years with occasional starting.
Strange thing is after I timed it earlier this year and it ran fine it always seemed to be giving a lean exhaust.

After this test I'm thinking rings or a bad head gasket some how... Exhaust had an odor and is visible (don't think anti-freeze though). I'm planning to install an O2 sensor for an air/fuel ratio meter so I can always get a positive reading.

Going to take the valve covers off tomorrow and see what I can find out about the valve train from there.
I've been wanting to do a strip down (even though it has low mileage) since its been sitting around for so many years, but been pushing it off... I guess this will give me the shove I needed!

 

[redsly]

Oh, stock block form from oil pan to valve covers, except carb and intake and it does seem to have excessive blow by, but that may be due to not having and breathers on the valve covers...

 

[EagleAutosports]

#8 doesn't sound good, the minimum psi considered within spec is 130 psi. #7 is right beside it and it's a little low in comparison to the others but it still sounds alright. You could have a bad valve guide or seat in #8, or a burned exhaust valve.

 

[redsly]

Thanks eagle. I was hoping it was just valve related. At least then its just head work and easier than tearing it all down.
I will eventually do that anyways, maybe a stroker in the future, but for now I can't make the vehicle to far from assembly in case I have to move this winter.

I understand low compression can cause carbon, but since you say the other cylinders seem fine then a rich idle would most likely attribute to this condition.
The carb came off my buddy's Chevy 350 and I never metered it or anything. It always had excellent power for what I had and EXCESSIVE fuel waste. I used to get 4 mpg city and 10 highway HAHA... :laugh:
Up until just a few years ago I never looked into how this particular carb works, but now I have a full understanding and have to get some metering rods and jets. The reason I never thought it was that was how the exhaust was white (lean condition). Although that was this year after I rebuilt it, many years ago it was black...

 

[redsly]

Ok...

Finally took my head off and saw this crap...

Numbers 5 & 6 cylinders look fine, aside from the head gasket looking like a little blow through from the #6 cylinder to a coolant port which I would assume caused the lower pressure in that cylinder. Damn fel-pro gaskets haha...

Numbers 7 & 8 had some scores on the piston heads near the outer edge (towards the exhaust), but the valves didn't show any damage what so ever. Perplexing...
When I turned the crank, after whipping the bore walls off, they left some oil. I understand that the walls need to be lubed, but they had more deposits on the lower (exhaust side) walls that seemed excessive. Oh, and cylinder number 8 had some burs near the top of the bore wall too.

Was getting ready to strip it down and rebuild anyways, but wondering what the hell happened here. I assume the guy lied to me about the mileage (looks like ring ridges going on) of this motor as well as possibly some head issues it had, but the carbon could have just been my poorly adjust carb originally on it.

For a 347 stroker, what does one need aside from boring it and I believe longer rods?

Here's some pics.