GregW said:
Hi Dave,
I’m curious if you think the DW crank was worth it. It looks like your peaks are designed lower than what the crank could handle. I had considered their crank, but when I added up the connecting rods, flywheel, etc.(since they only seem to work in a kit) it was way more than I wanted to spend.
Hi Greg,
DWR has a history of building fast durable engines, I trust their parts & quality. First, remember this is a very long stroke engine (4.375") & doesn't take kindly to higher rpm without a lot of help. It also explains why a 12 pound flywheel is not objectionable. The new crank, rods, & pistons were prompted by several things:
1- The stock crank frequently breaks at rpm over 5,000. I wanted to be able to turn it to at least 6,000 with a safety margin. The crank, ATI balancer. etc are good insurance.
2- The split pin clamping & design of the rods was questionable. On the stock engine, the rod big ends & crank journals are actually offset from the bore center lines. The new crank & rods are lined up with the bores. This is the reason that the non offset crank & rods must be used together. Each rod & piston weighs 1.25 POUNDS less than original which greatly reduces high rpm stresses. Having crank, rods, & bores on the same center lines also helps.
3- Since the crank was designed for eight bolt flywheel attachment, it made sense to go with a light steel eight bolt flywheel. I never was comfortable with the original 40 pound flywheel & four bolt attachment.
4- As aircraft owners know, metals that are cyclically stressed such as crank & rods, are subject to fatigue fracture & are replaced on a periodic basis even if they don't show signs of failure yet. I thought that at 90,000 miles & 50 years, the original parts had possibly reached the end of their "safe" life. It didn't seem reasonable to push these old parts to way over their original design limits. Stresses are expotentially increased as rpm goes up.
Yes, it was expensive, but you only get one chance to do it right. I know from experience long ago that exploding engines are also expensive & a lot of trouble. Worth it to me, maybe not to others. The down side is that none of this "good" stuff shows on the outside. But I know it's in there.
D