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4.5 issues

Started by funky d, 29 April 2009, 08:59 PM

funky d

I'll find time to do that again.
If it looks like I'm loosing comp. through the valves, Is there a way to check if there just dirty? Or would a rebuild be the only cores of action?
Where is the best place to get rebuilt heads? I would be happy if a top end rebuild is all i need!

koan

Quote from: funky d on 06 May 2009, 06:27 PM
Where is the best place to get rebuilt heads?

That really does depend on where in the world you are... give us a hint.

Do the compression test again, hot engine, wide open throttle, do it dry and then with a two or three squirts of oil in each cylinder.

koan
Boogity, Boogity, Boogity, Amen!

funky d

I'm in the western US.
I was thinking, the other day I was checking the valve clearance. I noticed that the back side of the cam (opposite the lobe) on each intake valve was dirty and shows no ware. Like it should where it dose not contact the rocker. The area that contacts the rocker of coarse is clean as it should. But the some exhaust lobes are clean all the way around, as if it makes contact the whole rotation.
The funny thing is, they all have good clearance readings.   .oo8in. on exhaust.
I would think too tight of clearance would account for my problem, but they are all in spec.
Any thoughts?

oscar

funky I meant to ask something similar a while back.  What should the back of any of the lobes look like, dark from the oil, or clean as though there's metal to metal contact with the rockers all the way round. 

Thing is, you can imagine that if they're dark from the oil, you know that the valves should close properly.  If the lobes are clear on the backside, well you'd expect that there may be compression leakage past the valves. 

Some time last year when I did the valve clearances on my 350, I ended up screwing down most of the lifters then back up again so the feeler gauges were dragged between the cam lobes and rockers.  Double checked measurements and all, but the engine was tappety as hell afterwards.  Next chance I got I took the rocker covers off again and found these gaps had widened considerably so there was no drag on the feeler gauges at all.   I don't know what happened.  i thought I was very thorough in my methods first time round and was sure I had used the correct gauges for the correct valves.  I readjusted the lifters again and used feeler gauges whilst pressing the rocker arms down with my other hand in case they weren't seated down firmly against the lifters.  All done and checked on a cold engine.  Engine was quieter but when I took the covers off yet again, some lobes had clean surfaces that were previously dark.  I never did a compression test as the engine seemed to still run fine but the affected valves had their lifters screwed down by a tiny fraction and I gave up on the feelers.  I reckon my method in getting the gaps spot on correct must have been amateurish and I was concerned to see the rear side of any of the lobes showing signs of contacting the rocker arms.  But I'm really unsure if any, even a light scrape, contact of the rear of the lobe with rocker arm is detrimental.  I would assume so but I don't know.

1973 350SE, my first & fave

pez

Koan is totally right - low compression there would be valve guides/seals, not rings.

I would also check some simple things on both banks - for example, the fuel injector seals, the intake & exhaust manifold gaskets, and also check for a crack in the exhaust manifold when it's cold [before it's expanded] to be sure there are none. All these could cause extra air to enter the combustion chamber, either before or after combustion.

funky d

Ok, finally did the test.
Dry test and wet test gave me the same numbers.
As you look at the motor...

143       115

150       140

145       140

150       140

The numbers did not change when I put about a cap full of oil in.
Not sure what that means, but there's the numbers.
I backed off the exhaust valves a bit to see what happens, so far nothing changed.

funky d

I think the noise actually got worse.
I'm just going to order another muffler and mask the noise. The car nuns ok for now and I don't feel like tearing the motor apart. Thanks for your help and if you think of anything else, I'll keep checking back.

oscar

Quote from: funky d on 08 May 2009, 07:28 PM
Dry test and wet test gave me the same numbers.

I was surprised to read that the other day so I went for a bit of a google to see how on earth that could happen 'cause it doesn't make sense.  I read one interesting reference that said for V8's, the slant of each bank meant that a tablespoon of oil in the cylinders isn't going to seal the rings properly.  Sounds plausible though there seemed to be plenty more people that said capillary action would see the oil move round the rings and furthermore, once you start the compression test, the test oil woild be forced into any gap that would otherwise allow a compression leak.  I've only done compression tests on I6's whos piston rings obviously get evenly covered with oil.

The only other reference I found mentioned that the valves may not be seating properly due to lifters being set too high thus allowing pressure to escape past the valves.  What is clear is that #8 cylinder is too low still.
1973 350SE, my first & fave

Papalangi

I'd double check firing order and condition of the plug wires.  You might have something I know as crossfiring.  By that I mean that the plug wires leak enough to fire an adjacent cylinder.

Michael
'83 300SD, I'm back!  It's the son's new car (12/2020)
1976 450SEL, 116.033  Sold it to buy a '97 Crown Vic.  Made sense at the time.
1971 250C, 114.023
1976 280C
1970 250/8

funky d

Ya, I've checked all that stuff. I did a resistance test on the wires  and tried moving them around too. I had an Accel ignition coil on it, so I took that off and put the old one back on to see what happens. Of cores, nothing.

I experimented with backing off the valve clearance bit by bit, starting with the exhaust valves. I got no change other than noisy valve. I have since put all the valve clearance back to spec.   
I know many cars drive around with low comp. on one cylinder without this problem. So I'm not convinced that is my sole problem. The car dose have good power and runs well enough to drive daily, so I think a rebuild would be overkill. If the new muffler doesn't  take care of the noise, I'll get back on trying to diagnose. Maybe the muffler just has some crazy resonance frequency happening with this motor???