Datsun Roadster Forum-311s.org

OK, as Rosannadanna used to say on Saturday Night Live, "nevermind"!

Ok, so what exactly has to be done? You're the perfect example of someone who has done it. I'm asking if the crank actually has to be shortened, and what mod has to be done to the keyway? Don't leave until you answer the questions. Thx Pat

70MTRoadster wrote: Wed Sep 08, 2021 9:16 am Pat, you might want to read my stroker article under the tech wiki, engine, Scott Lindley's stroker.

fwiw, Scott

Pjackb wrote: Wed Sep 08, 2021 1:22 pm
http://www.311s.org/pmwiki-311/pmwiki.p ... eysStroker
Scott Lindleys Stroker

2L crank from Florida. I had to shorten the 2L crank nose. I have a 13x40 Jet lathe and Grizzly milling machine and was able to part-off the nose to the correct length and machine a new single slot for the keyway. I was unable to drill and tap the nose though due to not having the correct centers to support the crank properly so took it to a local machinist and he charged me $50 to do this. We changed the thread to 5/8x24 and I used a hardened bolt and torqued to 140 lbs. I used the entire Motor Power timing set (cam gear, crank gear, chain, tensioner). The H20 crank gear had a .005 larger keyway slot in it than did the crank pulley from the 1600 so I had to make a double width keyway to allow for this.

unklpat wrote: Wed Sep 08, 2021 1:54 pm I read all of that,

70MTRoadster wrote: Wed Sep 08, 2021 2:23 pm OK, as Rosannadanna used to say on Saturday Night Live, "nevermind"!

unklpat wrote: Wed Sep 08, 2021 2:53 pm Ok, so what exactly has to be done? You're the perfect example of someone who has done it. I'm asking if the crank actually has to be shortened

Apparently, there is a difference of opinion among those who have done it. " I had to shorten the 2L crank nose" doesn't say why they had to do it.I'm not trying to be difficult, but when someone says they didn't shorten their crank, I listen. Are the people that didn't shorten their crank lying? The wiki has 2 or 3 suggestions, not the holy grail. Do we just do it, because rumor has it that you have to? I'm asking for specifics, and seeing that quite a few people have used U20 cranks in R16's, there must be some factual data out there.!'m asking for those that have experience with this process, to expand on exactly why they did or didn't shorten their 2L crank. There is no more need to quote the tech wiki, I've read it. Thx Pat

the U20 is an overhead cam engine so the lower pulley/chain is set further out on the crank as the upper pulley chain for the cam is closest to the block. the balancer is then also further out. Provided you cut the key ways you could potentially slide the gear and balancer further onto the U20 crank without cutting it, but you would need to work out how to hold the balancer on, eg with a spacer, as it would have an inch to float backwards and forwards otherwise. And a spacer with a 140ft lb torque is questionable. Much cheaper and easier to buy a H20 crank which just fits as is and keep the increasingly rare U20 one for a U20...

Fwiw, the Competition Preparation Manual (on the tech wiki) on page 24 has a crossview of the U20 engine showing the spacing

And just for fun - out here in Aus, there's good work being done on R24 versions...

Thanks Tomc18, all info is appreciated. Pat

Both options are possible. For example, Peter and I just had our strokers built at Rebello. I opted for the cut crank, which is Rebello's standard practice. Peter cares more than I do about preserving rare parts for posterity, and really didn't want to cut his U20 crank. He had a spare R16 pulley machined down as a spacer, and added the extra keyway needed to run the uncut crank. Both engine kick ass and made great power. Both methods take some work, and labor costs money. I think that's why several people have been suggesting the H20 crank for your project, which drops right in sans modification.

Hey Pat,

@funkaholik beat me to it and explained it well... but to be clear, you DO NOT HAVE TO SHORTEN THE U20 CRANK. Period. I know I'm a newbie, but I just did this. I did this because U20 cranks aren't a dime a dozen and if there's a way to preserve it, that's what I chose to do.

As Erik mentioned I had a 'spare pulley'. I used my original pulley (oh so slightly bent during removal) that my nephew turned down to use as a spacer. I bought a nice straight pulley from JT, and Voila. No-cut solution. Save The U20 Cranks!

My original R16 Crankshaft on the left, U20 Crankshaft on the right with pulley-turned-spacer in place.





I honestly didn't know that the keyway needed to be lengthened, and when I talk to Rebello I'll ask him about that.

Admittedly, it's maybe not as elegant as a cut crank, but it's fine with me, it did save me money, can still be used in a U20, and as Erik said, both solutions resulted in kick butt engines.

Good luck!
Peter

Thanks Eric, thanks Peter. That was my goal, to make this stroker reversable, while saving a rare crank, and some dollars. I have a machinist friend that might do whatever needed gratis, but thought it would be a good story for the owner to say the crank could still go into a U20. Also, H20 cranks aren't cheap,aren't as strong, and my crank was for sale, with rods, and possibly pistons/rings. The next step seems to be getting to the bottom of the keyway question. Any help along those lines would be appreciated. Thx Pat

Again, the keyway question has not been answered. Can we update the wiki, with current info? Thx for any help. Pat

I will update the wiki.

Steve

Thanks Steve

Jim, what exactly has to be done, to a U20 crank? enquiring minds want to know. You've put a lot of "stuff" out there, but what actually has to happen? Pat