Hey Folks,
I've got a 68 with a 302 that is smoking good on the driver side. I pulled the plugs and found the #5 and #7 plugs fouled. I changed all the plugs, changed the oil and filter and run it for about a week. I pulled the plugs again and found the #5 and #7 plugs fouled again.

For a final test, I went and bought me a compression tester. Per directions in my rebuild manual, I took the car out and got the temp up to normal. Came back, pulled the coil wire off, then started pulling one plug at a time, hooking up my compression tester and turning the engine over until the gauge quit rising.

Now, I assumed that my #5 and #7 cylinders would test really low. But they didn't...

#1 - 155 #5 - 145
#2 - 160 #6 - 160
#3 - 150 #7 - 155
#4 - 160 #8 - Didn't get this one.

...granted #5 is a little lower than the rest, but #7 tested great.

Am I cranking too long on the tests or some such?

Thanks

 

Did you pull all the plugs out before testing?

 

May be broke oil rings.

 

Well, no, [&o] I cheated on pulling all the plugs... I pulled one, tested that cylinder, replaced that plug and went to the next cylinder. Does that affect the reading?

I admit the manual said to pull all plugs, but figured it be less chance I dufus'ed up getting the wires back on the right plugs by doing one at a time.

 

Even though you didnt perform the test to the letter the #s are still consistant compared to each other. Someone correct me if Im out of line but compression doesnt seem to be the issue.

 

yes, that will give you lower readings..... Which means your compression is even higher then those numbers..........

 

even though that number five is getting close to the limit. It says the tolerance between cylinders should be no more then 20. It's still within those guidelines, but it's close.

 

Yeah that looks good. If one were around 90 or lower then you should be lookin for something wrong. Fords are quite efficient at wearing out valve seals. If you have one that doesnt smoke on start up then you dont have original seals. Think about changing them, also could it be fuel that is fouling the plugs and causing smoke? If its too rich or the choke is not coming off, it will smoke and foul plugs.

About the rings. Having an oil leak from the valve seals will help seal the rings on a compression test. We used to put some oil down the cylinders of engines we couldnt start, ie wrecked/salvage cars to find out the condition of the rings. A dry cylinder will not seal the rings as well as a slightly oiled one. To keep it all even we would oil them since when an engine sits for a time, usually two or more cylinders will have a valve open that entire time. Over a period of months/years that cylinder will dry out faster. Hence the reasoning behind the oil in a non running engine.

The pressures being that close is a good sign and 155 is right where a 302 should be for cranking PSI. A much larger cam with lots of overlap will bleed off some pressure, but if its stock that is really good pressures.

 

Thanks guys, I'm thinking I'll give it one more try "by the book"... I remembered this morning that I forgot one other step. The manual said to open the flaps in the carb as well, before testing. My thinking is, if it were due to running too rich or the choke stuck, wouldn't the symptoms be spread across all (or more) cylinders instead of just the two?

...this sure ain't as clear cut as that "How to rebuild your small block" manual put it. I guess that's just part of the fun.

 

If you are worried about getting the wires back on correctly, don't. Just follow the firing order, or you could even put a piece of masking tape on each plug wire with the number of cylinder it goes to before pulling them. And yes, if you are running too rich, all cylinders will be affected. I still think you have valve guides that are worn on those two cylinders.