Low Compression Problem (long)

[Florida_70Bee]

Hello,

I wanted to ask all you Mopar experts with a problem I am having.

Let me give some backround on what I am dealing with.

It's a 70 Super Bee original 383, Auto, 3:23 for highway cruising and 3:91's for when I go to the track.

The engine is the original 383 that was rebuilt in 1996 because of a thrust bearing failure. (the engine at the time had 39,000 miles
it now has 44,000) It was checked and boaring was not nessasary.

The rebuild consisted of:

1. The original flat top pistons were retained (like I said boaring was not nessassary)

2. Speed Pro plasma-Moly rings were installed (standard tension )

3. The crank was replaced however because of the thrust bearing failure.

4. The oil pump was replaced with a Melling high volume

5. New cam bearings and block prep was done (no decking was done)

6. The heads were rebuilt and harded exhaust valve seats were installed (No porting)

7. The original valve springs were pitched and MP "933's"were installed , new MP stamped hydraulic rockers, new MP retainers and keepers. I did keep the original rocker shafts.

8. The original pushrods were used but later pitched for MP pushrods because one of them bent later on

9. The cam and lifers I used was the 440 6 pack resto cam (I heard it was the same as the 383 magnums except that it has a 3 bolt cam sprocket instead of a 1 bolt sprocket.

10. A cloyes True roller cam and sprocket were installed "dot to dot" (no cam degreeing)

11. The original stock intake was used with original Holley 4bbl (about 585 cfm ,66 primary jets, secondary plate, 35 squirter, and yellow secondary spring)

12. The heat riser was blocked off with a Fel-Pro Valley Tray

13. The distibutor is the original single point (29 degree dwell angle) that has been recurved by replacing the heavy spring with Mr Gasket light spring for Mopars

14. The exhaust uses the original 383 magnum manifolds with stocks 2 1/4 dual exhaust and Hemi Mufflers .

The car has performed great for several years (it ran a 14:70 with the 3:23's and 14:41 with the 3:91's on F70-14 Polyglas no less!)

But recently I noticed what sounded Like a "Putt-Putt" sound coming from the drivers side exhaust pipe at idle. Cruising was fine..
I have check and adjusted the following in order to find the problem with no success..

1. Dwell angle on the distributor

2. Carb for any leaks and readjusted (even jetted up and down as an experiment)

3. Tried different carb

4. Check for vacuum leaks (found none)

Well, after this I decided to do a quick compression test (cold engine,carb at idle and not WOT)
I found the following: All cylinders are at 150 lbs except for cylinder #3 which was at 80-85 lbs.
The first thing I checked were the pushods on that cylinder because a few years ago one of the original pushrods bend and broke so I replaced them with MP pushrods. The pushrods were straight...

So my questions are:
1. Where do I proceed from here? What other tests can I run and how do i do them?

2. Do I check the lifters to see if the cam lobes are wiped ? If so how can I identify it? Will the lifters be dished ?

3. Do I check for a bent or burnt valve? If so what do I look for?

4.Would it be a broken or weak valve spring? If so how do I check?

5.Could it be a broken ring? How do I check? (I hope it's not this)

6. Is there anything else I have missed?

By they way can anyone convert the 150 lbs to an estimated compression ratio?

Thanks for any help you can give me!

Florida_70Bee

[KETTERING]

Shoot some motor oil in the cylinder with low compression and try the compression test again. If your compression rises to the level of the other cylinders, then most likely the rings are not sealing. If your compression does not rise to the level of the other cylinders, then the valves are not doing their job. I hope this diagnoses your problem.

[dynorad]

Get a leakdown tester. They aren't too expensive and you will be able to pinpoint your problem.

[Glen440]

The engine likely needs a little disassembly so you could check the lifters(If a valve doesn't open you'll have like 30psi). Instead of a leak tester you could also pull the manifold while the intake is off and put compressed air in the cylinder and see if any gets past the valves. I'm pretty sure none should get past with rockers off. That will tell you if its the head. I had a prob and did comp tests and found all had 160 and one had 30. It was a wiped lobe on the cam.

[gwaii]

I agree with the other fellows that say you might have a wiped lobe on the cam .you said that it had bent a push rod before on the number 3 cylinder for what ever reason and i suspect that the lobe on the cam may have been damaged at that time.putting in new pushrods cured the problem but the damage had already been done and just needed time to expose itself.I had a demon with a small block that did the same thing with the same noise.what i did was pull the valve covers,had some one turn it over and watched the rockers and i found one that was not opening indicating the wiped lobe on the cam.

[PRO]

a putt putt from the exhaust means compression is escaping into the exhaust that shouldnt,you have 1 of the following,burnt exh valve,stuck valve,bad cam lobe,or possibly a fail hardened seat,that is its come out of the head this happens rarely if the interference fit isnt tight enough,BTW installing hardened seats should really be accompanied with newer valves the reason is the valve face gets the hottest and transfer the heat to the head when it seats,adding seats helps the head but not the valve,valves of the pre emission era arent as durable as emission stuff.With 85 psi the leak will be obvious,unbolt your rocker shaft(closes all valves)and apply air pressure to that cylinder and listen for the leak at the intake(from inside the carb,this would be a bad intake valve)at the exhaust pipe tip(bad exh valve),or from the valley pan area(bad rings)it could be a wiped cam lobe especially since you bent a pushrod before,you may have too much lifter preload which shortens the cams life,hope this helps ...........PRO......

[Goldfish]

My guess is a burnt exhaust valve. I've seen many chevy's eat cam lobe's but havn't seen any mopars. I'll tell you that if you have a wiped exhaust lobe it will pop through the carb becouse the pressure that is built up in the cyl. on the exhaust stroke has nowhere to go but out the intake valve when it opens. If you don't have access to a leakdown tester you can use your compression tester, that is if you have the kind that has a seperate hose for screwing into the cylinder with a regular air hose conection at the other end. All you have to do is take out the shrader valve in the end of the compression tester hose then you can air up the cylinder. The only thing is you need a regulator becouse you don't want more then 30 or 40 psi or you'll push the piston down in the hole and open a valve defeating the purpose. I bet if you can do this you'll hear air escaping out the tail pipe.
Just my two cents.
Glen

[Florida_70Bee]

Thanks for all the tips! You guys have been great! Keep them coming!

I am going to try and borrow a leakdown tester. I have already removed the rocker shaft from that bank of cylinders and I will test for the burnt valve. (Hopefully that is all it is..)

PRO I have few questions..

I beleve I did replace the exhaust valves with MP's but I need to check on the old receipts when the head was done.

What is the procedure to test the amount of preload I have on the on the lifters? Dial gauge? Feelers?
How much preload should I have?
I assume I fix the problem by adding shims under the rocker tree am I right?

If I pull out a lifter and its dished then the cam is wiped.. correct?
Could It be a collapsed lifter?? If so how do I check?

The pushrod that was bent was an original one (The type with the rolled steel look to it ) It actually broke in half and was laying down in the lifter valley. That is when I replaced all the pushrods.

Okay. Other questions I have.

What would the 150lbs relate to in an estimated compression ratio? 8.5:1, 9:1 or 9.5:1?

If the cam is wiped do guys have any suggestions on a cam that will give me the same vacuum at idle (15 to 16 Hg) deliver more Hp and torque than the 383-440 magnum cam.
I want to run this car occasionally at pure stock musclecar events with the 3:91's. Or do I use the magnum cam and advance it a few degrees?

[Florida_70Bee]

Okay I am going to test the bad cylinder this afternoon. I have a compessor with a regulator and the hose to the compression tester that will fit on to the air hose end. How much air should I pump the cylinder up to. is there anything else I can do..
I could not get a leakdown tester..

[Florida_70Bee]

I FOUND THE PROBLEM!

Like you guys suggested I took the hose from the compression tester and removed the core from the spark plug end of the hose. Then screwed it into cylinder #3 and attached the other end to the air hose which had an outlet pressure of 85 psi from the compressor (thats what I set the regulator to) and listened.

The air was not coming from the valley area (whew that was a relief..) and it was not coming from the carb but it was coming out the exhaust pipe. I could feel the air on my hand when pressed on the pipe so that is how I definately knew.

So I unbolted the head on that side and put it up on my workbench The exhaust valve on #3 was the same color as the others but when I flipped the head over (rocker side down) that is when I found my problem.

I shined a light below on the exhaust port of #3 and I looked at the valve in combustion chamber. I could see a hint of light shining through exhaust valve seat area of #3!

Now I've got to get someone to fix it!

I also checked the lifters on #3 they were not dished as well as the other cylinders so I believe the cam is still in good shape.

Thank you for all your suggestions.. They were a great help to me. I will keep you all updated if you all are interested.

By the way here is a link to pictures of my car. A friend of mine allows me to use part of his website for my car. Thanks again!

http://www.71superbee.com/1970/images/

Florida_70Bee

[beeman]

Sorry to change the subject but what color is your superbee. I have a alpine white 70 with back interior. 383 pistol grip.

[Florida_70Bee]

Beeman

My car has 44,000 miles and has the following equipment
FE5 Red with a black bench seat interior and white "C" stripe
(95% of which is the original paint and interior)
383 Cubic Inch “Magnum”
Carburetor 4 Barrel Holley 585 C.F.M.
Air Induction Optional “N96” Ramcharger Fresh Air system
3 speed wipers
Ignition Single Point Vacuum Advance with retard selinoid
727 Torquefite Automatic 2.45 1st,1.45 2nd, 1.00 3rd

A31 Axle Package which consisted of
(Rear End 8¾ with 3.91 ‘Sure Grip’
26 Inch Radiator with 7 Blade clutch Fan
Power steering cooler)
Brakes HD 11 Inch Manual Drums
XHD suspension)

Tires F70-14 Goodyear Polyglas
Wheels 14X6 Steel with Deluxe Wheelcovers (Although I have rallyes on now)

Here are some more pictures of if for you.

http://www.71superbee.com/1970/images/

Florid