I have a c4 hooked up to my flathead using a speedway adaptor kit . After about 2 years of driving the flywheel cracked . Contacted speedway and got a new flywheel . They said this was unusual and provided the new fly wheel at cost . Now after about 3 months of driving I belive this flywheel has cracked also . Will know for sure when we get into it . I don't think this is the result of a faulty product . Something is causing this but I don't know what .The mechanic shop I use is local, been in business many years , and I trust . Has anyone had this problem ? Or have any ideas on the cause .

 

Where is it cracking at? Between bolt holes? Somewhere else?

 

As I recall the crack on the last one was on the inner part of the flywheel between bolt holes . We havn't got this one apart yet to check .

 

That sounds like the adapter isn't centered properly, i.e., the t.c. centerline is offset from the engine centerline. That causes the flex plate to flex far more than it is designed for.

 

There should be offset pins on the bellhousing

 

You mean in the adapter?

 

You got some flexing going on. Something not concentric-- break out the
dividers micrometers and dial indicators. How is the converter seal
holding up??