PDA

View Full Version : Dead Motor ?

cmetzner
10-23-2006, 02:59 PM
Took my car to a Miata specialist to track down the source of an increasing and annoying 18 month old vibration. His verdict was a bent crankshaft. He measured the endplay.

I have the car at another shop now for a second opinion.
Tom @ Fast Forward
10-23-2006, 09:27 PM
Chuck, is it a 99 or 00? If so, they should check for the old thrust bearing problem. A lot of those engines were built with the wrong thrust bearing (back by the #4 crank journal). There was a recall, I believe.
cmetzner
10-24-2006, 12:30 PM
Mine is a 99. There never was a recall just a TSB. The #4 bearing seat was cut incorrectly and therefore the stock bearing was too small for the size of the cut in the block.

Mech said that could have caused the bent crank; that or a bad harmonic damper or excessive side load. He pretty much assumed the block would be no good. I have heard of some owners dropping the pan and replacing the bearing with an oversize bearing.

He said the crank was bent because the crank endplay was .004" with the crank in one position. He then turned the crank 180* and the endplay was .008". The measure was consistant over 4 repetitions.

I have the car at another shop for a second opinion.
Tom @ Fast Forward
10-24-2006, 04:23 PM
The TSB was for the Thrust bearing which is located in the #4 journal area but the problem was not the #4 bearing itself. They put too small of a thrust washer in some and that allowed the crank to mover fore and aft and wore the thrust bearing more until the engine gave up. I don't think a bent crank was associated with the thrust washer/bearing problem?
Mathrips
10-24-2006, 06:00 PM
Post this on Miatanet and see what the folks on there say. I am curious to hear a viable explanation. Remember that mechanics are sometimes guessing.
cmetzner
11-05-2006, 01:18 PM
I had the car on the track for my and its first time. It was at Willow Springs - the road course. You would think that if something was wrong it would get worse there. Car was fine.

I rode along with a pro Miata driver driving my car. WOW - never had an experience like that. This guy has been racing Miatas for 5 years and is a Mazda team driver.

Also gave me a ride in his Carrera.

One of the most fun days that I have ever had. Changed the oil in the car and the vibe does not seem as bad.

Maybe that driver shook something loose.

The engine builder that was there said he never heard of a bent crank and suggested that I change the harmonic damper.