Compression Test results

[Wbruiser2]

I'm back again with an another off the wall issue. Since I bought this truck back in July I have slowly but surely fixed most of the major and minor issues and when it comes to the engine, fix one thing and something else is revealed like the timing, then an off idle stumble, etc... So where I'm at now is, I have some what of a stumble and this is the best way I can explain it: If I start it and while at high idle, the tack will drop about 100rpm every few seconds. Driving down the road I can hear it and feel it. Its annoying and not noticeable when accelerating even though I'm sure its there. So I did a compression check, dry and cold. All the cylinders were between 145-150 except #5 which was about 130 and #3 which was 120. I did one side at a time and took all 4 plugs out on the particular side. So 20% difference between the highest and lowest. I've read and heard 15% is good but also between 120-150 is good. I don't know but here is what I got:
Remanufacured 302 bored .60(according to PO) and about 5000miles on it.
In the past 6 months: New plugs (Autolite 25), wires (summit), distributor (Richporter), and msd coil. Doesn't smoke whatsoever. Gets about 10-12mpg.
Could I be looking at a ring problem or something to do with valves? Or something totally different? All though I didn't do the compression test by the book I think no matter how I did it that one was a lot lower than the other..

 

[5.0Flareside]

Well ill say this, why would you buy a truck with a 302 that is .060 over?!?!?


I'm not trying to be rude but .060 over is way overboard.


But now to try to fix your problem.. What's your timing set at? What kind of carb is on it?

To me seems like a fuel delivery/carb problem..

 

[Fellro]

When you do a compression test, all plugs are to be out. They say to have the throttle wide open as well, but I am guilty of not doing that. 20% from highest to lowest is generally acceptable.

 

[SuperCab]

Yeah, your compression test results sound fine.

Sent from my iPhone using Forum Runner

 

[Wbruiser2]

...20% from highest to lowest is generally acceptable.

Thanks... The more I read about it I'm finding that to be the consensus.

 

[Dirky]

Well ill say this, why would you buy a truck with a 302 that is .060 over?!?!?


I'm not trying to be rude but .060 over is way overboard.


But now to try to fix your problem.. What's your timing set at? What kind of carb is on it?

To me seems like a fuel delivery/carb problem..

I see a lot of this .060+ "Voodoo" garbage. There is nothing wrong with boring an engine over .060 in order to achieve a round bore, assuming wall thickness is adequate. You could Have a .90-.100 thick wall in an engine that is not abused and never have a problem. I guess the thinner your wall, the more your cooling system is compromised... Unless you're revving your engine to 6K all day long or racing, you need not worry. The less you need to bore, the better, of course, I just felt like "ranting" a bit I guess.


No need to make a guy worry about something that he shouldn't.

Your problem almost sounds ignition related, I'm surprised that the symptoms aren't more noticeable during acceleration...

 

[Wbruiser2]

I see a lot of this .060+ "Voodoo" garbage. There is nothing wrong with boring an engine over .060 in order to achieve a round bore, assuming wall thickness is adequate. You could Have a .90-.100 thick wall in an engine that is not abused and never have a problem. I guess the thinner your wall, the more your cooling system is compromised... Unless you're revving your engine to 6K all day long or racing, you need not worry. The less you need to bore, the better, of course, I just felt like "ranting" a bit I guess.


No need to make a guy worry about something that he shouldn't.

..

Thank you for the rant, couldn't have said it better myself

 

[smokey]

I agree also, have rebuilt many 302 with a 60 over bore with no ill effects at all.

I see a lot of this .060+ "Voodoo" garbage. There is nothing wrong with boring an engine over .060 in order to achieve a round bore, assuming wall thickness is adequate. You could Have a .90-.100 thick wall in an engine that is not abused and never have a problem. I guess the thinner your wall, the more your cooling system is compromised... Unless you're revving your engine to 6K all day long or racing, you need not worry. The less you need to bore, the better, of course, I just felt like "ranting" a bit I guess.


No need to make a guy worry about something that he shouldn't.

Your problem almost sounds ignition related, I'm surprised that the symptoms aren't more noticeable during acceleration...

 

[5.0Flareside]

I disagree but I'll let it go... Sorry..

 

[DNFXDLI]

I disagree but I'll let it go... Sorry..

What do you find so wrong with a .060 overbore?.

 

[5.0Flareside]

just personally i feel its too much.

but dirky is on the right track of why... thin cylinder walls compromises cooling if your beating on it at all or towing.

if your getting into it at all RPM wise the bottom of the cyl walls are super thin and have a chance of breaking.

now i realize this is a pickup and not a mustang but just 1 time of laying into it can bust it.

just one to heavy of a load can over heat it and cause a meltdown cause combustion chamber temps..

it's all personal preference.

 

[DNFXDLI]

I just don't get your reasoning......060 over is not uncommon...now, if you start talking .125, I understand

 

[5.0Flareside]

i've seen several .060 overs just grenade or massivly overheat... .030 over or .040 never have an issue..

i dont understand how just 2 hundreths of an inch is such a difference but there is from what i've seen..

 

[Dirky]

i've seen several .060 overs just grenade or massivly overheat... .030 over or .040 never have an issue..

i dont understand how just 2 hundreths of an inch is such a difference but there is from what i've seen..

We're talking about thousandths, not hundredths..

Do you know what you're talking about man??? Haha just teasing!


I'm sorry for taking this thread so far off topic!

 

[5.0Flareside]

it can go either way...

30 thousands or 3 hundreths.. doesnt matter really..

 

[DNFXDLI]

i've seen several .060 overs just grenade or massivly overheat... .030 over or .040 never have an issue..

i dont understand how just 2 hundreths of an inch is such a difference but there is from what i've seen..

I would guess that there were other underlying reasons that came into play.
I have seen just as many engines overheat and other problems with anything from no overbore to over .125.
But as you said, it's whatever you are comfortable with.

 

[Dirky]

it can go either way...

30 thousands or 3 hundreths.. doesnt matter really..

X2 on Duncan's comments

 

[Mil1ion]

What carburetor is installed?
Are the throttle rod bushings worn out on either side or both ?
Is the throttle rod set at the proper setting
Do some tests with can of carb cleaner to check bushings

 

[Wbruiser2]

What carburetor is installed?
Are the throttle rod bushings worn out on either side or both ?
Is the throttle rod set at the proper setting
Do some tests with can of carb cleaner to check bushings

It has a 570cfm Holley and everything seems tight and adjusted correctly. In the past while looking for vacumn leaks, I sprayed carb cleaner on the throttle shafts and it bogged it down when I sprayed the throttle side. Is that a sign of a bad bushing? I tried looking at an exploded view of it and I didn't see any bushings. As far as I know the carb is only about three or 4 years old and maybe has 3000 miles use.

 

[Mil1ion]

More than likely the bushings are worn out and leaking

The bushings are thin and between the rod and the carb casing

Some ppl think a rebuild kit will fix a carb but they forget that No bushings are included and ...a good rebuild is when the carb is sent away for a COMPLETE rebuild
Go to the holley site for a diagram


Details are everything !