HELP!!! terminal engine vibration!!!

[Tommo560]

Hi Guys,

I am new to this forum and my name is Tom Whitfield. My dad and I have recently just purchased a highly modified competition spec English Datsun 260z, and we are having some troubles with it. When the engine reaches about 4000 RPM a vibration is experienced from the engine. The engine is an L28 and has racing cams, triple Weber carburettors, high spark (???) spark plugs, has been recently bored, polished and blueprinted and has flat top pistons and an L26 head. The previous owner has told us that he had had a lot of trouble with the harmonic balancer but since buying a solid gold BMW harmonic balancer the problem seemed to be fixed. Anyway i was wondering if any of you guys have had this problem and might know what it is. Anyhelp in this matter or any tips for anything to look out for would be greatly appreciated.

Cheers,

Tom.

[4381821]

well, I'm new at this myself, but think it sounds like the motor wasn't balanced correctly.

I broke the original harmonic balancer and bought the NISMO euro damper single groove replacement. I also scored a sweet Fidanza 10.5lb Flywheel for cost. With these alterations, the machine shop said the best money I could spend would be on balancing all the rotating mass. They gave me all of these horror stories, and told me their own personal blunders with not doing so especially when running higher RPMs. Chevy heads may tell you its a waste, but talk to a stock car racing chevy guy, and he'll even say it's a must when running RPMs.

[zeiss150]

maybe check your motor mounts? Are all of your pistons firing? Thats all I can think of.

Matt-

[Fun_in_my_z]

Check ur plug wires to.

You might have gotten a lemon.

[Ed]

I would think that unless the internal balance is way off you wouldn't really notice any vibration. I think you might have a problem getting a consistent spark. Try this, rev the engine until you experience the vibration, hold it there. Then pull a spark plug wire off the plug. Do this one at a time. Each time you disconnect a wire you will notice a difference in the way the engine runs. Do this to all six until you find one that doesn't make a difference.

Good luck.

[Tommo560]

Thanks guys,

Dad seems to think that it might be internal balance problems so we are going to take the crank out and get it balanced. but i will try the spark plug thing too.

Cheers,

Tom.

[zeiss150]

Hey tom, Im sure you know this but when you ballance your engine you need to ballance the whole thing as follows... crank, pully, pistons, rods, rings, flywheel, clutch pressure plate (and all the bolt that hold that stuff on). I had my engine ballanced and It revs up to 6500 smooth as slik. Good luck!

Rock on Z people!

Matt-

[Mr Camouflage]

^^^^ Ditto What zeiss150.

No use balancing the crank if the every thing that hangs off it is out of balance too. All your conrods and pistons have to weight the same. But maybe you mean the whole engine, when you say crank?

[Tommo560]

dad just mentioned the crank as everything else should allready be the same weight, but if it is as you mentioned then we will have to balance the whole engine.

Tom.

[Carl Beck]

Tom:

Does this vibration problem exist Past 4000 RPM -or only around 4000 RPM?

I wouldn't just to the conclusion that it's a balance problem, until I was certain that everything else is perfect. You mentioned triple webers... who sat them up and dialed them in? How much dyno time has been spent on the car?

Past checking to assure that the crank pully bolt is at the proper torque - and that it isn't slipping around then checking that the flywheel bolts are properly torqued, then checking that the main bearing caps are properly torqued.... I would seriously doubt that anything is so far out of balance that you notice it at 4000RPM.

I'd bet it's ignition or fuel related if everything is torqued properly.

Hate to see you pull an engine down - until you are certain that's the problem.

FWIW,

Carl

Carl Beck

Clearwater,FL USA

[zeiss150]

I agree with Carl. I doubt it would be the engine balance. balancing the engine should be the last thing you do. check all the stuff that carl mentioned first and try everything eles that you can think of before you break down that engine.

Good luck, Matt

[Tommo560]

carl,

the engine vibration starts to occur at around 4000rpm and just gets worse further up the rev range, but it disapears at below 4000rpm.

Tom.