Compression test results and running warm

Hey everyone,
Sorry about the length of this post...
Background:
I'm still trying to get my engine figured out here. I've got about 3500 (I think) miles on it now, but it's still having some issues. It's had a vibration pretty much ever since I finished the rebuild that I thought was caused by the transmission. It was rpm related, and would shake the whole car. You could feel it very obviously in the seats and shifter.
A couple weeks ago, I swapped back to my old 8.5" flywheel/bellhousing/clutch/2.77 transmission/driveshaft to see if that would fix it. It did get a little better. Now you mainly feel it with your hand on the shifter, but it does seem to start vibrating more of the car above 70 mph. It gets stronger and faster with higher rpm.

I've had a couple people tell me it definitely has a miss, so since the trans swap didn't get rid of it, I'm guessing that's my vibration. I've used the LOM and a DS2 distributor, a couple different ignition modules (Mopar and HEI), a couple sets of plug wires, multiple sets of plugs and different gaps, and 3 different coils (stock, Pertronix, TFI). Vibration remains the same with any of it.

First question (compression):
I did a compression test a couple days ago. 5 cylinders were in the 165-180 psi range. Cylinder 2 was at 105-110 psi. I added some oil, and it came up to 115-120. Does that sound like a valve issue, and would it maybe be bad enough to cause a noticeable miss and vibration? I have another head I can try.

Second question (temperature):
It's finally warming up here. On days that it's like 70 or above, my temperature gauge starts moving past the halfway point, up to above 2/3. It only moves up that high when I'm on the highway. When I'm idling or doing about 30, it sits about 1/2. A few days ago, I pulled the rad cap after it sat for a bit and measured the coolant at about 192. Today I did it right after shutting it off (though it was on the cooler side of the gauge by then), and I think the highest I saw was around 140. The head itself was anywhere between 180 and 215. It has a 160F thermostat, so this seems off to me. Is it?

Thanks!!

Q1. Yes that much of a difference in compression can cause bad vibration. Did you do a valve job on the head? Check to see if the valve stems are taller then the others on the head if so you could try a shorter push rod if the they are the same then you have a poor valve seal.

bubba22349":g12m322y said:

Q1. Yes that much of a difference in compression can cause bad vibration. Did you do a valve job on the head? Check to see if the valve stems are taller then the others on the head if so you could try a shorter push rod if the they are the same then you have a poor valve seal.

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Yeah, the shop did a valve job, resurfaced it, and installed hardened seats. I'll check the valve stems tomorrow. Thanks.

Well the valve stems are a bit all over the place--I guess that's to be expected on a 50 year old head. Cylinder 2's stems were roughly the same height as the other front cylinders. The biggest difference was on cylinder 6, where the exhaust valve looks like a good 0.040"-0.050" below the ruler I laid across them. I'm pretty sure I checked the preload and sized the pushrods based on cylinder 1 or 2, so they should at least be close. It may not be a bad idea to order a couple of the shorter pushrods just as a check though, since that's a lot cheaper than a head swap.

With #6 cylinder valves closed, put compressed air into the cylinder & that will find the leak.
Air out the exhaust, air out the intake, or air from the crankcase. That will pinpoint your problem area. Good luck.

1: wsa111 is spot on with a leakdown test. Easiest way to tell where a compression problem is.

2: I would personally not rely on the factory gauge to tell you anything for certain about engine temps, but generally speaking an engine that is hot at freeway speeds and cool on the surface streets has a restricted radiator. Maybe have it cleaned, recored, or replaced.

wsa111":3kq834fg said:

With #6 cylinder valves closed, put compressed air into the cylinder & that will find the leak.
Air out the exhaust, air out the intake, or air from the crankcase. That will pinpoint your problem area. Good luck.

Click to expand...

thesameguy":3kq834fg said:

1: wsa111 is spot on with a leakdown test. Easiest way to tell where a compression problem is.

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I unfortunately don't have an air compressor. I should have access to one this weekend though, so I can give it a try then.

thesameguy":3kq834fg said:

2: I would personally not rely on the factory gauge to tell you anything for certain about engine temps, but generally speaking an engine that is hot at freeway speeds and cool on the surface streets has a restricted radiator. Maybe have it cleaned, recored, or replaced.

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Thanks. I do have another temp sensor I can try out; I just need to convince myself to get the fittings and do it lol. The radiator was replaced when I put the rebuilt engine in, so it should be fine unless it isn't good enough for some reason. It's just a cheap stock-style one. I'll have to get that other sensor in and see what I can figure out.

Is it possible you have poor belt tension, and the water pump isn't keeping up with the motor at higher rpm? Check for polishing of the water pump pulley as well as belt tension. Maybe hit the groove with some ~200ish sandpaper to give it a smidge of texture?

thesameguy":3652jl9e said:

Is it possible you have poor belt tension, and the water pump isn't keeping up with the motor at higher rpm? Check for polishing of the water pump pulley as well as belt tension. Maybe hit the groove with some ~200ish sandpaper to give it a smidge of texture?

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As far as I can tell the belt tension is fine. The pulley has a bit of shininess to it, but not too much. I'll have to check it out a little more. The temperature dropped around here, so it's hard to tell if it's still running warm or not.

As far as the compression, I was able to get the air compressor hooked up this weekend. With cylinder 2 sitting at TDC on the compression stroke, there was a steady flow of air out the exhaust. I also tried it with the rockers loosened just to make totally sure the valves should be closed and it was the same leakage. So it looks like it has a leaking exhaust valve there. Guess I'll be ordering some head bolts and everything to swap over to my other head soon.

Well swapping the head didn't help as much as I hoped it would. :/ I haven't run it much yet since I just finished a couple hours ago, but it looks like it shakes a little less at idle. Unfortunately, I still have a vibration on the highway. That's apparently another vibration. Now I'm noticing that if I put it in neutral on the highway the vibration is largely still there. I hadn't noticed that so much before the past few days. That's kind of weird though since I'm back to everything being the way it used to be except for the engine.

This is frustrating lol. At least it looks a little better since I repainted the head and the exhaust manifold while I had them off...

what about the carb leaning out at wot? That could lead to higher temps at freeway speeds but cooler running at idle maybe? Might also have caused a valve burn on the exhaust valve on 2? What did your valve and seat look like on number 2 when you switched heads?

when you say you still have vibration in neutral, is it the same as in drive, or less? What about in gear but clutched? I had a speed related vibration that was my drive shaft, and also once where I flattened out my tires slamming on my brakes. You seem on top of things in all this so I think you'd have caught the difference between speed and rpm vibration but it doesn't hurt to ask.

as far as the different stem lengthens on the valve job, IMO no, that should not be expected on a head with a fresh valve job with new hardened seats installed. They make the cuts, they press the seats, they should make sure they are all the same. IMO (and I have lots of opinions).

for an rpm related vibration, with all the work you've done to figure this out, I have to ask about the rebuild:
1 did you do it, or outsource some/all of the work?
2 why did you rebuild, and was there a vibration? (I assume no previous vibration)
3 did you have your rotating assembly balanced? Static or dynamic too? Did you balance your pistons/rods?
4 what accessories do you have? I don't know if a ps or a.c. Pump would vibrate, but you could take them out of the equation, same for the fan for an idle test.

I think it's your rotating assembly, especially if it was the same shop that did your head. Also, cc your chambers, different valve stems mean different sear depths and different chamber volumes. Could mean nothing, or could be exasperating lean conditions on those front cylinders.

electrorc":2w3lhmjc said:

but it looks like it shakes a little less at idle. Unfortunately, I still have a vibration on the highway. That's apparently another vibration. Now I'm noticing that if I put it in neutral on the highway the vibration is largely still there.

Click to expand...

A few simple things you could do to help sort this out.

While on the highway with the trans in neutral and the vibration pressent turn the engine off and see if it's gone.

With the engine fully warmed up and at idle use a IR temperature gage to check the exhaust tube temps individualy. If one or two are either to hot or cold this could show you which one is at fault, ie to rich, to lean or no spark. If all checks out then maybe a mechanical problem.

Thanks Invectivus and Mav, let's run through this...

Invectivus":r608prol said:

what about the carb leaning out at wot? That could lead to higher temps at freeway speeds but cooler running at idle maybe? Might also have caused a valve burn on the exhaust valve on 2? What did your valve and seat look like on number 2 when you switched heads?

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Well I'm very rarely at WOT, pretty much just when merging. But when just cruising, I feel like it's probably rich. I'm only getting ~17 mpg highway, my pistons seem to already have a good bit of carbon build-up on them, and my spark plugs are gray IIRC. I took pictures of the head after I pulled it off, so I'll have to get those up soon. But the valve face itself was sort of a whitish-gray and seemed to look fine to me otherwise (though I don't know a lot lol).

Invectivus":r608prol said:

when you say you still have vibration in neutral, is it the same as in drive, or less? What about in gear but clutched? I had a speed related vibration that was my drive shaft, and also once where I flattened out my tires slamming on my brakes. You seem on top of things in all this so I think you'd have caught the difference between speed and rpm vibration but it doesn't hurt to ask.

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I would say it's probably about the same, maybe a little less. It kind of varies. Just revving it sitting there, it always seemed the same in gear with the clutch in. I think that's one of the biggest things that's throwing me off... it kind of seems like it's both speed and rpm-related. If I hold 2nd to 3k, it'll vibrate similarly to on the highway. And now of course I'm seeing it vibrate at idle on the highway. I don't know if I'm chasing multiple problems or if I'm just really bad at recognizing its behavior...

Invectivus":r608prol said:

as far as the different stem lengthens on the valve job, IMO no, that should not be expected on a head with a fresh valve job with new hardened seats installed. They make the cuts, they press the seats, they should make sure they are all the same. IMO (and I have lots of opinions).

Click to expand...

That's what I was thinking, but this is my first one so I wasn't really sure. The other head I just put on doesn't seem to have them quite equal either.

Invectivus":r608prol said:

for an rpm related vibration, with all the work you've done to figure this out, I have to ask about the rebuild:
1 did you do it, or outsource some/all of the work?
2 why did you rebuild, and was there a vibration? (I assume no previous vibration)
3 did you have your rotating assembly balanced? Static or dynamic too? Did you balance your pistons/rods?
4 what accessories do you have? I don't know if a ps or a.c. Pump would vibrate, but you could take them out of the equation, same for the fan for an idle test.

Click to expand...

1) A local shop did the machining, valve job, and short block and head assembly. I did the oil pan and pump, lifters, pushrods, rockers, bolted the head on, etc.
2) Shortly after I bought the car 3.5 years ago, I found I had a completely broken pushrod, and a few others that were bent. I knew nothing about engines then, so I took the engine to the shop and they told me it needed rebuilt. It has a different block now, but I had kept the same head. No vibration when I first bought it.
3) Unfortunately no, nothing was balanced.
4) No accessories, just the water pump, fan, and alternator. I ran it without the belt once and it didn't seem to change anything with it sitting there revving it.

Invectivus":r608prol said:

I think it's your rotating assembly, especially if it was the same shop that did your head. Also, cc your chambers, different valve stems mean different sear depths and different chamber volumes. Could mean nothing, or could be exasperating lean conditions on those front cylinders.

Click to expand...

Yep, same shop. I did cc the first head; I'd have to dig up the results for it. It seems like they were all within about 2cc or so from what I'm remembering. The 2nd head I only did a couple of the chambers.

69.5Mav":r608prol said:

A few simple things you could do to help sort this out.

While on the highway with the trans in neutral and the vibration pressent turn the engine off and see if it's gone.

With the engine fully warmed up and at idle use a IR temperature gage to check the exhaust tube temps individualy. If one or two are either to hot or cold this could show you which one is at fault, ie to rich, to lean or no spark. If all checks out then maybe a mechanical problem.

Click to expand...

I'll try to remember to try that on the highway tomorrow.

I don't have an IR temp gauge unfortunately. I did try it with the temp sensor on my multimeter after it was suggested to me before and I want to say it was #4 that was a little warmer than the others, maybe 10-15 degs.


I feel like I have to be missing something really, really obvious with this whole mess. I think I'll probably try to find someone local sometime here too that can at least give me a second opinion on its symptoms... Thanks again to all of you that keep helping me!

electrorc":22xmps28 said:

I don't have an IR temp gauge unfortunately.

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IR gages are cheep but you could do it old school. Get an empty dish soap bottle and fill it with water. Squirt each exhaust runner with water and gage it temp from how the water boils off (or dosen't).

Hi electrorc.Just curious.Have you checked for the correct balance of the tires?
Good luck.Have fun.Be safe.
leo

Alright so I'm either chasing multiple problems or doing a very poor job with one of them haha. It does feel like it's smoothed out a little bit at higher rpms now, though not as much as I feel like it should've.

I also shut it off on the highway a few times. The vibration was still noticeable with the engine off. It does seem to change between having the engine running and in gear versus having it in neutral or off. With it off or in neutral, it seems like it's still mainly with your hand on the shifter that it's noticeable. I'm not totally sure how to describe the change though.

Right now though, about the only difference from when I first bought it is the engine (and the floors)... hmm.

woodbutcher":3dn663af said:

Hi electrorc.Just curious.Have you checked for the correct balance of the tires?
Good luck.Have fun.Be safe.
leo

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No, I haven't specifically checked them. They're the same wheels and tires that were on it when I bought it, and I didn't have a vibration issue then. So unless a weight fell off between then and last year, they should be fine.

Maybe the driveshaft needs balancing.

electrorc":3tygthlp said:

I also shut it off on the highway a few times. The vibration was still noticeable with the engine off.

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This tells me that you have at least two sources of vibration.

Check tires and wheels for ballence. Check the drive shaft for any missing u-joint retainer clips.

Did you check the engine exhaust for imballence in temperatures. If you have a miss it should show up as a colder exhaust outlet tube.

You can also try removing one spark plug wire at a time and watch for a drop in RPM. The cylender with a miss will show the smallest drop in RPM.

Good Luck

69.5Mav":jli2wg8o said:

This tells me that you have at least two sources of vibration.

Check tires and wheels for ballence. Check the drive shaft for any missing u-joint retainer clips.

Did you check the engine exhaust for imballence in temperatures. If you have a miss it should show up as a colder exhaust outlet tube.

You can also try removing one spark plug wire at a time and watch for a drop in RPM. The cylender with a miss will show the smallest drop in RPM.

Good Luck

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Well for what it's worth, I ran it on jack stands again. I pulled the rear wheels and drums off and the vibration was still there--though it may have changed a little with them off. I also rotated my driveshaft around. I think that helped a little bit. Since I've been all over the place with my posts, it is currently on the original driveshaft which worked fine before. I did replace the u-joint though, so maybe that threw it off a little bit. No missing clips that I could see. Since rotating that shaft helped a little, it looks like it'll be a good idea to find somewhere to take my other shaft and have it balanced.

I just checked the exhaust a bit ago with the water. It boiled off pretty much instantly on every cylinder (taking some of my manifold paint with it :/ ). Pulling plug wires results in what seems like the same change with each cylinder.

I also checked my DS2 distributor again, and it definitely has some play in the shaft. I threw my LOM distributor back in with points just to see what it did. It didn't help the idle, but it does kind of feel faster now haha. Guess the DS2 definitely needs some work with the tune and advance curve...

electrorc":1owmuvsd said:

I ran it on jack stands again. I pulled the rear wheels and drums off and the vibration was still there

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Well, that eliminates alot. The only things left are the transmission, Drive shaft, Differential and the Axels.

I would look at two areas. The drive shaft and the Axels. A bad wheel bearing on one of the Axels could cause a vibration so I would look for one or both of the Axel ends to be loose when you try to wiggle it or make noise when it rotates though this could be hard to detect.

Good luck and keep trying to narrow it down.