A few years ago, I spun a wrist pin bushing necessitating a crankshaft rebuild on my 2008 FLHTC. While in there I changed cams to a set of Woods TW 6-6. These cams need more compression so I had about 0.040" removed from the heads and installed a 0.030" Cometic head gasket. I had figured this to be around 10.5:1 static compression ratio and about 9.8:1 corrected compression ratio. Maybe I am way off I don't know. Anyhow recently my crank pin failed and I had to send my crank back to Darkhorse for another rebuild. Darkhorse feels as if the failure is consistent with failures seen in high horsepower, high compression ratio race engines. I didn't even need compression releases. My engine turns over fine even when hot. My question to all of you is do you think this is truly the reason my crank pin failed? Does everyone with high compression ratio need compression releases? I know lots of you guys have compression releases. Have any of you had crankshaft failures with these high compression engines? Any thoughts?
I am going to reassemble with stock head gaskets to detune it a bit. Hope this helps.

 

Not to contradict the good folks at Darkhorse, but that statement would be in regards to excessive pressure being generated on the crank bearing ie, "high compression".
Thinking along those lines, how would a 124" at 11.2 cr with a Wood 9F ever make it down the road?
The pressure if you will, is being transmitted to an actual bearing consisting of cages, hardened rods(now)a case hardened crankpin, and fully hardened rod rollers.........odd.
Scott

 

Everything Scott said plus: I would dare say that the vast majority of cranks done by DarkHorse end up in "high compression" motors, yet very few fail. Even 99-02 stock HD factory crankshafts hold up in some very hot motors. That response from them is lacking. Might want to consider an S&S crank this go round...

 

10:5 to 1 is far from a high compression engine. I would start looking at the oiling system if your having repeat crank pin failures.

 

Thanks. I didn't think I was too high in compression. He said the crank pin failed at TDC. They found the HD part failed so they charged me full price on a crank rebuild. It is already done and on its way back to me. I don't know what to do. Do you suppose I should detune with the stock head gasket or try it again as I had it? Wouldn't I need compression releases if I was to go "too" high in compression?

 

If you were generating "too much" compression, you would be 1), experiencing spark knock or dentonation so uncontrollably you would not to ride it and 2), it may not even want to start correctly.
Me thinks something else is at the root of this issue.
Scott

 

Thank you very much.

 

Who are you talking to at Darkhorse? Doesn't sound like the type of response I have gotten from my past interactions with them.

 

I was talking to John. He was really concerned about my deck height. I kept telling him that it was stock down there. Is there something about stock setup in the piston and cylinder that is inconsistent that he would be asking me about that? The only thing about deck height that isn't stock is the fact that they use rods that are 0.003" longer than stock but he knows that. Anyhow, here is a picture of the crank pin. it is about 1/3 of the way around it and about 3 or 4 bearing rollers were also rough. The rough spot feels about 0.010" deep or so. I will take it to work and get the metallurgy guys to tell me a better story of what failed.

 

Very Interesting thread... Subscribed......keep us updated .... Thanx..