1970 Cadillac 472 valve job, car knocks under engine load-Solved THANKS

[Scot Minesinger]

Hi,

Had a valve job done on my 472 engine in my Cadillac.  The engine was rebuilt about 20k miles ago, but they installed used heads rather than rebuilt ones and the car always burned oil and smoked at start-up and at take off from a light.  The valve job cured this.  I could have done this myself but the time it would take (I'm still working 70 hour weeks with the the stay at home Mom and three kids) would make it a year long project.  I used a very reputable shop and the mechanic is very experienced.

Before the valve job the car really ran well, getting 14 mpg on the highway at 75mph trips with a/c on.  The car had good power, idle smoothly and etc.  I'm a perfectionist about having a durable car so finally had this done at the end of the season.

The engine was pulled out and the engine bay and engine were detailed and repainted so it looks great under the hood now.

The only problem is the car knocks under any load.  When I first got the car back it knocked under the most minimal load.  It was converted to electronic ignition prior to the work (similar to how a 1975 might be), and then I had it converted back to original look with the polysonics (or whatever it is called) electronic ignition with original external coil replacement.  I retarded the timing back 9' from the setting the shop did and it has helped some, but there is not much room left for further retarding. 

I have checked for a vacuum leak and not found one.  Have a vacuum gauge hooked up and during idle at in park it pulls 24 inches, in drive at idle 20 inches.  The gauge is a real good Autometer type and the gauge does not pulse or fluctuate.

Is there some error that could have been made in removing heads and all that could create this type of knocking problem?

Thanks,

Scot

[62droptop]

are you talking spark knock??only under load,worse when you floor it at low rpm?

if the heads were mackined on the gasket surface to true them up, the compression would have been increased also
if you are experiencing spark knock, first try premium fuel if youo are not already using it
and you may have to retard the timing a bit
maay have to pull the distributor to realign the driveshaft/camshaft relationship to allow further retarding of the timing
sounds like you have a great seal as high vacuum readings
other than the knock,how does it run?


how old is the fuel? i presume you had to add fuel since the job was done?
possibly shitty fuel as a bunch of years back i filled up my truck with 30 gallons of less than good fuel at a service station
i had to add 3 litres of methyl hydrate and 2 bottles of 104 octane boost just to get the thing to run
it made all kinds of nasty spark noises and knocks before i added all the additives

hard to diagnose over the computer without being there but we will try our best

[Dave Shepherd]

Common cause of this could be the egr valve not working, once warmed up spark knock can occur if it is inoperative.  Also make sure the thermal air intake is working also.

[Scot Minesinger]

Thanks for help so far, please continue.  Yes, clarification, knocks only under mild to hard engine load/acceleration.  Have retarded the timing down to about 3' (factory setting is 7.5').  The timing retarding was done incrementally and each time it improved.  Guess I will have to realign the distributor with cam shaft another tooth to get much more timing reduction.  The gas is good.  I drive the car 4 to 5k miles per year, never letting a week go by without a drive, except once and a while around snow with salt applications in the winter.  It runs OK, except for the knocking.  Just checking to make sure a valve job error would cause a problem.  It is connected to ported vacuum (vacuum to distributor actuator increases when throttle is increased).  There is no EGR valve.

[Dave Shepherd]

Right on the egr, Calif only.  If you have to go back that far on the timing something else is gopng on, these engines had 10.5 compression, which of course today requires at least 91 octane, as mentioned if the heads were trued or the head gasket is thinner than oe, the compression could be higher. I would see if some race gas helped then you would know it is likely the compression has been raised somehow.

[cadillactim]

Scot

If you add some octane booster to the fuel, and the knock goes away, then you know it's a fuel probem that you will need to address with timing and/or higher octane fuel.  Might need to change where you get your gas.

Tim

PS  Got my website back up. Has a new look. Check it out.

[Bob Hoffmann CLC#96]

NO EGR's on any Cadillacs until 1973...
Bob

[TJ Hopland]

Hows the vacuum advance?  Was it perhaps replaced when the the distributor was put back in?  The aftermarket replacements seem to have a lot more advance range in them than the originals did.  I have not messed with the points ones for a while but I presume you can buy or create a way to limit their travel. 

Is that the year that has the open exhaust cross over under the carb that used a special base gasket?  Maybe the gasket has or is burning up and you got a vac leak leaning things out?

["Cadillac Kid" Greg Surfas 15364]

I*'m with TJ on checking the vacuum advance. Check it compared to factory specs for inches to start, inches at full and what vacuum causes full.
If you are getting too much advance at light throttle you can definitely get a "rattle" if that is what you are getting.
Greg Surfas

[CaddyShackPA]

Hi Scott! Have you driven the car with the vac advance disconnected and plugged? My '69 knocked on 93 after I replaced the leaking factory vac advance with a supposedly-correct replacement, even when properly connected to ported vacuum. Disconnecting the vac eliminated the problem and I had to change vac advance hardware to get it right. You mentioned having gone back to a Pertronix-style ignition so not sure if that was done at the same time or what else, distributor-wise, was changed. If truly nothing was changed other than the valve job to cause this, do find out how much the heads were cut...

If you have access to a dial-type timing light (and perhaps a hand-held vac pump) it's easy to document how much lead you're getting from both the centrifugal and vac advance systems and compare that to manual specs.

[Viator Trudeau]

re: 1970 ,472 knocks:   comments about compression changes, A compression check W/ engin hot should show much more compression than a normal no knock engin W/ factory timing??

Viator Trudeau

[Alan Harris CLC#1513]

I had a 1970 years ago. My recollection is that that these cars had something called TCS or transmission controlled spark, which blanked out the vaccum advance until the car was in high gear.

If you knock on acceleration, are you sure that the spark is not advancing while you are in the lower gears? Premature spark advance would give you the problem that you describe.

[EAM 17806]

NO EGR's on any Cadillacs until 1973...
Bob

I thought EGR valves were introduced in 1974 with HEI option only and then in 1975 forward when HEI became standard. EAM

[TJ Hopland]

All my 73's have EGR and none of them were CA cars.

I didnt think that speed spark control thing was used for that many years.  I only ever saw them on 72's. 

[Scot Minesinger]

Yes there is a vacuum solenoid activated by the transmission for emissions only.  In first and second gear, the timing will under normal circumstance not be able to be advanced by vacuum.  In third gear and reverse it will receive the ability for the timing to receive vacuum advance.  The position of the solenoid before it is installed is to allow timing advance.  You might think that if the solenoid failed that then you could have knocking due to advance vacuum timing in first and second gears that should not be there.  However that is not true. 

This is in evidence by examining the wiring diagram associated with the transmission kick down switch.  When the accelerator is depressed strongly, the car down shifts and in so doing the transmission vacuum advance solenoid is also de-energized allowing advance timing to be activated during strong acceleration in first and second gear.  I thought about this too and came to this conclusion.

I'm getting the car back from the bodyshop today and will tinker with it further.  The hood hinges wore oblong holes in the members at the rivets and caused the hood to rise about 3/8" above fender near the windshield - took the springs out and - viola perfect alignment.  Had hinges restored by SMS in NH, and they look magnificent!  Now I have a nice closing hood the body shop tells me.  Probably the hood wore out from all my opening and closing.  I'm too much of a car/engine nut for my own good. 

Thanks for all the advice.  It seems clear that we have an adjustment problem as I had hoped, rather than a mechanical problem associated with a valve job error.

Happy New Year,

Scot

[Scot Minesinger]

Thanks for all the help.  The problem was actually not pre - detonation, but a noise resembling it and occurring only under engine load.  The flywheel cover had been removed and I guess dented in slightly during the work.  The flywheel would impact the cover only under a load, but not during idle or normal operation.  That has been corrected and the problem is gone.

Scot

["Cadillac Kid" Greg Surfas 15364]

Scott,
Not to cause you any mental grief, but there is nothing that should move laterally (backwards and forwards) in that area unless your crankshaft's thrust bearing is worn excessively.  Transmission problems are usually the cause of the thrust bearing wear.
Greg Surfas

[Gene Beaird]

Hmm, agreed.  When you get some time, you should probably crawl under the car, remove the cover again, and look for:
1. loose bolts at the converter-to-flywheel mount,
2. loose bolts at the crank-to-flywheel mount,
3. cracks in the flywheel.  I'd carefully inspect for cracks in the flywheel.
4. cracks or breaks in the welds that attach the ring gear to the flywheel.  That will _usually_ manifest itself in other ways like grinding or clunking noises when trying to start the car.

Looks like you get another opportunity to lift that hood.   

[Scot Minesinger]

Thanks for the further advice on the flywheel attachment and integrity, it certainly is easy to check.  Will do.  I have to get under the car sometime in the winter because the gasket has failed on the tail section of the transmission with the six bolts anchoring it to the main section of the transmission (is dropping fluid slowly).  I tried tightening the bolts to no avail.  The car runs great now, but I will check these things out.

[Scot Minesinger]

Car was running great, but just to be safe and because it is easy, I checked the flywheel out.  It is in real good shape, no cracks, teeth look great and the bolt to the torque converter were properly tightened.  However one bolt on the flywheel cover was not tight due to stripped threads and I was able to effect a nice repair.  So I am better off for investigating, thanks for the advice.