I finally got around to tearing my race engine down after it failed the oil pump gear and I found that the root cause was a loose crank damper bolt.  The bolt loosened six hours into a race and allowed the damper to walk out some.  At that point, the crank gear could slide fore/aft on the crank which took out the pair of gears.  Also, the damper began to wobble which beat up the crank snout and ruined the damper bore.

My plan is to buy a new damper, probably an ATI from Summit Racing.  Once in hand, I'll take the damper and the crank to an engine machine shop and see if the crank can be saved.  I've heard they need to be sized anyways, so maybe they can take a few thousandths off the snout and salvage the crank.  After a lot of research online, I see that the ATI pulley is much smaller than the OE pulley.  Has anybody had an issue with cooling or charging due to the ratio change?  It's an endurance racer, so charging wouldn't normally be an issue, but we do need to run several sets of headlights for night races and it will get an electric cooling fan upgrade.  Next question is the bolt.  MSA sells a higher quality bolt from Kameari, but I don't know if the length is right for the ATI damper which I've read requires a longer than stock bolt.  Datsun Spirit sells an ATI kit with a bolt and a belt, but their price is $200 higher than the same damper from Summit and the Kameari bolt from MSA.  I like supporting Datsun shops, but paying $200 more for the same part seems silly.

 

Which ATI damper?  ATI makes three different ones for the Datsun L6.  One is smaller (about the same as stock) and the two larger ones are available in two weights.  It appears Datsun Spirit sells the lighter of the two large diameter dampers.  Summit Racing stocks all three.

What bolt to buy and what is the right length?

Any issues with underdriving the alternator and water pump?

Any idea why yours failed?  Was it a stock Nissan damper?  Wrong bolt length or washer?  Looks painful.

Bolt came loose.  From what I've read, that isn't super uncommon.  I've never had one loosen before, but now I will be sure to use Loctite and check it often.  The engine had 20 race hours on it before this happened.  

Stock parts?

Since my stock damper is now unusable, I need to get a damper no matter what.  Since the performance dampers are known to be a tighter fit than stock, my hope is that I can salvage the crankshaft.  If not, I have an old engine I can tear apart for the crank, but that one is an unknown and might need work and or bearings too.  This crank is good other than the snout.  My teammate thinks we should upgrade now to a better damper for (hopefully) future reliability.

Whatever you use Jeff, make sure the crank bolt isn’t too long. I used a Nismo performance crank bolt once and it was a tad too long (for the stock damper) to pull everything up tight. Took me a while to figure that one out. Just make sure you are torquing threads and not the bolt bottoming out, or you’ll go through the same problem again. BTW, my guess is a performance machine shop can weld and machine that snout. If they can change the stroke on a stock crank, don’t know why they can’t fix the snout.

Guy

 

Edited July 6, 20186 yr by Diseazd

Thanks Guy.  Do you still use stock, or did you upgrade on your latest build?  BTW, do you recognize the damper in the picture?  

In the past, I’ve only used stock dampers.....280 dampers bought new from Nissan. My two Stroker Motors used expensive dampers (ATI Super Dampers)....Eiji built those two motors. My guess is that’s the one I sent to you. If I use stock dampers, I always use the stock crank bolts....lesson learned.

Edited July 6, 20186 yr by Diseazd

So what brand did Eiji use on your strokers?

Ahh, perfect.  Do you know what model number ATI that is and what bolt you/he used?

ARP doesn't make one and MSA only lists the Kameari bolt which might or might not be the right length.

4 minutes ago, Jeff G 78 said:

So what brand did Eiji use on your strokers?

Not sure on the numbers Jeff, but any good speed shop (Summit) will have those numbers and my guess is the bolt came with the damper. It takes a special tool to install as you can see.