I had a weird noise that appeared on my '74 Cutlass last summer, when I was on a long trip. I was 600 miles away when I heard it on startup. It always held excellent oil pressure, and had balanced compression. However, I never could figure out this odd noise, and actually had another engine ready to go in it . I had my original 350 rebuilt back in 2013, with 493000 miles on it. (It had weak compression in number 7, due to valves, and used oil. Hasn't never used a drop in the 30000 miles since then. Upon removal, I discovered 4 cracks in the flexplate, around the torque converter bolt holes. Installed a new flexplate, which fixed the issue. I am going to use the rebuilt 350 in my Dad's (RIP) '76 Pontiac Ventura that came with the 260 Olds. Note, that this is not an easy issue to track down, but I am glad I found it. I could have prevented this by installing a new flexplate on it back in '13. I am thinking this got cracked due to metal fatigue over very high mileage. Any thoughts on this?? Could shift kits in the transmission contribute to it? Anything else?? Just curious what people's input is. I am thankful I found it.

 

Age possibly

 

 

I'm sorry. I can't see the cracks in the lousy pictures.

 

In your 1st picture you can see what appears to be 2 witness marks . Some thoughts on this, 1. While it could be age related metal fatigue, you can see 2 indicated marks of bolt tightening imprinted on the flex plate. I would check the torque converter for imprint marks on the inside of the flexplate mounting points as your bolts might be too long, it doesn't take much. I had experience this on a engine with 310,000 miles and suspected it was caused by metal fatigued when it turned out to be the torque converter bolts being long enough to leave marks on the torque converter.

 

Thanks. I will definitely check the bolts on the new flexplate.

 

Sorry if it is hard to see. They are around the inner holes that the converter mounts to.

 

I've had a couple of cars with cracked flexplates over the decades. In both cases, the bolts from the trans to the engine were loose, causing the flexplate to flex more than intended and thus causing the fatigue cracks.