327 serious problem
 

This is a stock rebuild of a 250hp 327 (owned by a friend). The engine only has 100mi on it and it was pulled due to a severe vibration. I can see that the exhaust valves show signs of over heating, but I'm not sure what the deposits are on the pistons. Maybe it's running so lean that it's melting the aluminum? He says the plugs are "clean". He was using Sta-Bil in the gas.

Any ideas anyone?


Verne


Attachment 181283

Attachment 181284

Severe vibration? Explain more? Is the harmonic balancer bad? Is the crank straight? How is the flywheel or automatic flex wheel? Sounds like to me its out of balance with parts i am listing? Not enough info to figure out what he means by this severe vibration? Was the timing to far advanced? Carb adjusted correctly? This engine does not have high compression.

The vibration might have been severe detonation, but that should have cracked the ceramic in the plugs. It does look lean, but I'm no expert.

Did it do it after the rebuild or after a few miles?

Got a pic of the plugs?

I can ask for a pic of the plugs. He said the vibration starts at about 1200rpm and gets worst up to about 35-40mph. He can feel it in the seat and it's bad. He said all the normal suspects have been checked, ie: tire balance, driveshaft, pulleys. The mechanic said he checked the crank and its good.
Right now my question is what caused the appearance on the piston?? The mechanic says the problem is the gas and the carb and that's why he was referred to me. But I disagree that a carb problem would cause a vibration. Maybe a miss or hesitation, but not an actual vibration.
I'll be speaking with him later for more info.


Verne


He just sent this pic of a plug. They all look like this and they look fine to me.
Attachment 181322

Could it be the harmonic balancer has spun on the rubber ?
I had this problem years ago on a L-S6, unbelievable vibration.
Bruce

Catastrophic Engine destroying detonation can be heard from the roadside when occurring on a passing vehicle.

WOW those valves look overheated.
Piston looks like cooked on oil -
a flat top in a 250 hp 327 hard to believe there were detonation.

Are all four tires balanced? Has the car been given a proper alignment? Has the car been sitting for a long time on it's tires? Maybe the tires have flat spotted?

I mentioned this too. Harmonic balancer could be bad. Never heard of a bad vibration caused by timing. I am sure the timing was set correct when starting engine and then make sure it was correct before driving the car. Same goes with the carb. To me if he got 100 miles on the engine without the bad vibration, then all of the sudden it started and can feel it when sitting in the seat, it could be a drive train issue. Before i would of ever torn the engine back down i would of done some real research on the problems i mentioned. Driveshaft out of balance? bad u-joints? loose flywheel, flex-plate? This is not a hi-perf engine here. Have the crank checked again. Out of balance? Check harmonic balancer. Check complete drive train. Dont over look anything. Its could be an obvious thing. Let us know.

The black stuff looks like deposits from octane booster. You wouldn't think it would need octane booster with flat tops. Can't imagine he put enough Sta-bil in there to cause deposits.

Pretty easy to isolate engine vibrations from anything else. If it is in the engine, it will vibrate with the car sitting still. If you suspect driveline, turning the engine off while coasting in neutral will eliminate the engine.

I'm still waiting to hear back from him. I need to hear what tests he did and when the vibration started. I'll definitely pursue the balancer issue. He did say he used an octane booster. The 250hp engine was rated at 10.5:1 CR.


Verne

Wrong flywheel/flex plate? Seen it happen way to often.

Well, I just got off the phone with him. The car had no vibration at all before the engine rebuild. It was run without all the pulleys, trans and flex plate disconnected and the vibration was still there. He even pulled the balancer and stuffed a cardboard tube on the crank to keep the oil from running out and it still vibrated.
Supposedly, the crank was retested for balance and passed. I suggested he find a good shop to check the crank again, making sure the rod journals were ground at the same distance from the crank centerline, and weigh the rods and pistons again.

He's sending me the carb to go through and fix the lean issues.
I told him to skip the octane booster and lead substitute in the future.

Verne

Verne to me if that engine had no vibration before the rebuild but developed one after the rebuild, something was not done right then. Sounds like the engine is completely apart now. Going to have to go thru everything again with a fine tooth comb and see what was done and was it done right. Have the rods checked for out of round and straightness and have them magged for cracks. Sounds like he had the crank double checked and its fine. So now take a hard look at the rods like i mentioned and then the pistons. Check pistons for cracks and piston pins too. Check push rods, lifters, rocker arms, etc. There is definitely something wrong inside. Even get the engine balanced while he is at it. It doesnt cost a bunch and you know everything is good. What kind of carb is this engine using? A Q-JET?

As mentioned -Check the weight of the rods-
I know this is a 327 but I seen it before on a 396 where someone used a single non dimple rod in the rebuilding of a 396 L78 that was 6 grams off and destroyed the engine in under 2500 miles

Did the shop who machined it put in a exchange crankshaft? It’s either cracked or the bob weight figure is way off. Was it balanced? I had a shop screw up the bob weight calculation 1 time by figuring in 2 small end connecting rod weights. I would also make sure the flywheel & balancer is a non counter weighted style.

Agree i mentioned balance too. This engine just seems like a real mess. Maybe a
wrong rod, crank is bad, on and on. I mentioned do a complete visual inspection on the bottom end. And also mentioned a complete balance job on the crank, rods, etc. Vibration means something is totally wrong with the rotating mass.

Agree. I was thinking detonation due to an extreme lean condition, but the plugs show otherwise.

The carb is the correct Rochester 4GC. I believe the crank and rods are the originals. Reportedly they did some "shaving" on the rods, so they are suspect. The pistons are new, but they are being cleaned and will be weighed. The valves appear to be new but I don't know about the other valve train pieces. I doubt any of those parts could cause a vibration. As I said before, the trans, flex plate, pulleys and balancer were removed and it was test run and still had the vibration.
When I talk to him again, I'll suggest the balancing. He should take those parts to another shop for that.
He said he adjusted the mixture screws using a vacuum gauge but I forgot to ask him what the readings were. There might be a leak which would cause the lean condition. I'll ask him if he has the correct PCV system hooked up. I want to know those things before making any changes to the carb.

Verne

Verne, shaving on the rods? interesting. Maybe he meant polishing the rods and removing the flash and possible shot peen. But shaving could of meant lighting them up somehow. But if material is removed from a rod, you need a balance job on the crank and rods. His best bet would be to buy a good set of news rods on the market and lighter. Agree valve train should have nothing to do with this vibration problem. I always been big having an engine balanced anytime you have it apart for a rebuild or building an engine. You will be amazed how smooth they run. Racing engines are always balanced. IMO i highly doubt its a carb problem. You are right see what happens to his changes first before a carb rebuild. Keep me posted.

Hey Verne - any updates on this? Just curious.

The last I heard was that he was in contact with another shop that specializes in racing engines. He planned to take the rotating mass parts to them for evaluation and balancing.
He sent me the carb and its done and he has it back. I found a lot of the settings were off, but not enough to cause a lean condition. I did find a partial blockage in one of the primary venturis which might explain why the idle mixture screws had such different settings. I also found an incorrect PCV valve which I replaced with a correct NOS one. I sent along an installation procedure I had written up which details the correct installation and final adjustments needed after its running.

I'll reach out out him and find out where things stand now.


Verne

Over on the NCRS boards DUKE WILLIAMS - states the following regarding older 327's
"The connecting rods are weak and should be replaced. The Eagle SIR 5700 is a good choice and a set is only about $250. It's the least expensive insurance policy you will ever buy."

If the rods were "massaged" I hope they were mgnafluxed.

I would check the wires and cap, were they installed correctly with the firing order or was there a crossfire from one wire to another. Also was the engine balanced, possibly show some pics of the balancer and flywheel. Could be externally balanced parts? Just looking for any possible cause.

I'm still waiting to hear back from him. I know he said it ran as smooth as glass at idle, so I don't suspect any ignition problems. The vibration started at about 1500rpm.



Verne

The vibration IMO isnt an ignition issue with his 327 engine. As i stated a couple of months ago it has to be in the rotating assembly. Anytime you rebuild an older engine, new rods should be purchased. The time and money to size, magged the rods and check for straightness that money could be spent towards some good Eagle rods or Manley rods. But IMO if you have a good used Muscle car engine numbers matching, IMO i would keep as much of the original parts as i could. Just me. But if you run a street and strip engine, new components should be used.

That's all good advice and I'm well aware of the limitations of the stock rods. However knowing how his car will be used, I see no harm to keeping the original rods, as long as no one has muffed them up.


Verne

Nothing wrong with using the later small journal rods for street and some strip use as long as new ARP or other quality rod bolts are used.

Hey Verne, Take that motor to Pete's Automotive.

I think he lives in CT.


Verne

Verne, agree, no harm to keeping the original rods as long as they check out good. New rod bolts a must and check for out of round and straightness and magged for cracks. But like you said if someone did screw them up the vibration could be caused by that and they should be balanced. I a big fan of balancing an engine.

Honestly from what I can see you have a low end rebuild there, do yourselves a favor and find a competent shop to rebuild your engine correctly, especially if its a nice car the engine goes in, you will be happy in the long run.

Just an update for those who are interested. I just heard from him. He was in the hospital for two weeks. A surgery coming up, then he needs to recoup. The engine was picked up and it's at home. When he's able, it will be taken to a good shop to look into it.


Verne

Thanks for the update Verne, Sorry about his hospital stay. Hope he gets this 327 figured out. That bottom end needs attention for sure.

Does it have the correct flywheel without an external weight ?

Good morning!!
Question regarding ban617 question, can you explain a wee bit "correct flywheel without an external weight".. Was there ever a crank flange with a weight added to it back in the late 50s and or early 60's? I seem to remember that I have such an sbc crank like this.
Maybe the ole memory is gettin' hazy, but .... ???
Take care gentlemen!
Ted

He may be referencing the SBC 400 or BBC 454 flexplate/flywheel required for external balancing ...

327 serious problem
 

Check the distributor for mechanical or vacuum advance problems. I've seen first hand where the nylon bushing under the mechanical advance plate where the weights and springs are located crumble and become missing allowing way too much mechanical advance. Try things that do not cost money to begin with. Also check valve guides in head for oiling issues, look for cracked seats in heads. Check oil rings placement and gaps. Also check end gaps on compression rings. For 100 miles, that's a lot of oil on piston tops! Thanks, Don.

The rebuild from the get go does not sound good for starters. Looks like a lot of small issues leading up to a very bad vibration in the bottom end and then deciding to pull the engine and have it gone thru again. This engine needs to be completely torn down and everything visually checked, then parts magged, check for straightness, out of round rods and crank tolerances measured. Were the correct parts used. Highly recommend a balance job also.