4.1 crank

[noslo6]

From the responses so far, I guess you are right I'll have to do the legwork myself if I want to make this work. I know it's the wrong one, why else would I be here asking if anyone had made this work before? I guess this is the best response the board can come up with, some one telling me to scrap it all. Well that may be the best solution for some, but at the point I am at now, it would be more cost effective to have a custom flexplate made than tear the whole engine apart and purchase another crank.

 

[Intercooler]

I guess hindsight is 20/20 with comparing the one that you took out to the one you wanted to put in. Sounds like a lot of work to maybe still be untrustworthy or have issues later. Hate to say it but I think you are going to have to invest in a couple of gaskets and a little time to change it out. Good luck!


BTW.... I have a 20/20 CORRECT and checked crank pretty cheap

 

[ijames]

Are there any other differences at the other end of the crank that will bite you later, if you get an adaptor? The 3800 cranks drive a gerotor oil pump directly, and may have different spacings between timing gear and harmonic balancer, and I think they use a different balancer for that matter, with an 18x interrupter ring for the crank sensor. KendallF in the stage II forum has made an adaptor front cover to use the gerotor pump on a stage II block, and hopefully he will see this and chime in on any differences he knows about (hi, Kendall ). Good luck.

 

[noslo6]

Good topics that I did check into. From the research I've done on the internet, it seems both cranks are identical except the rear flange. I've contacted a custom flywheel company and the guy said he could do it for me no problem. I have to send him one of each of the flexplates, my original and a new one that will fit the 3800 crank just for references. He would then manufacture a new one using chromemoly and balance it to match my original all for around $150.00. The crank installed perfectly using a new timing chain set. My balancer fit perfectly and timed perfectly. I don't forsee any problems after I get the new flexplate. It's gonna take about 2-3 weeks to manufacture. I'll keep everyone posted as to how it turns out. If someone has another solution before I send the flexplates out, please don't hesistate to give your opinion as I want all the info possible.

 

[KendallF]

Originally posted by ijames
Are there any other differences at the other end of the crank that will bite you later, if you get an adaptor? The 3800 cranks drive a gerotor oil pump directly, and may have different spacings between timing gear and harmonic balancer, and I think they use a different balancer for that matter, with an 18x interrupter ring for the crank sensor. KendallF in the stage II forum has made an adaptor front cover to use the gerotor pump on a stage II block, and hopefully he will see this and chime in on any differences he knows about (hi, Kendall ). Good luck.

Hey Carl. The nose should be the same; the difference is in the lower timing gear (the gerotor ones have an extension with flats to drive the pump) and a consequently shorter hub on the balancer.

I say go ahead, make the custom flywheel, put the kitty litter in the trunk, and go for it. Just take pictures of any results, OK?

 

[noslo6]

Why would you think this crank would fail? It has rolled fillets on both rods and mains and I had it cryo'd to boot. The only difference between this crank and a turbo crank is the flexplate flange. The flexplate I'm having made is made from chromoly steel and I'll use the best bolts money can buy. Where's the problem?

 

[ijames]

Considering that a GM flexplate is about $140, if this is a way to use the late model, plentiful crank and if it is just as strong, for $150, I say GREAT!. Tell your flexplate guy to put some on the shelf . Oh, I think you will also need to tell him the distance from some reference surface on a crank journal to the starter gear/converter mount surface, to make sure it's the right distance. (Thanks for the input, Kendall.)

 

[Lee Thompson]

Just a dumb hillbilly thought

The 4.1 and the 3.8 use different flexplates. Now, all else being the same on the two eng. except the bore size (Piston weight ) How are you going to know how to balance out the flexplate? Also how do you know the cranks counter throws are not different in weight.
That is what Kendall was saying about the kitty litter.
I suppose you could have compared on a balance machine.
Just hate to see you spend $ on a plate that won/t work out.
Reguardless, keep us informed on how it comes out

 

[b4black]

I have a book (V-6 Performance by Pat Ganahl) that talks about the opposite situation. The were swapping a RWD crank into a FWD car (a 4.1 into an X-body 1980 Skylark). They offered the possibilty of machining the larger RWD flange down to the FWD flywheel.

Buick engineers stated that they have successfully done this in the past, but they feel that the extremely small flywheel bolt pattern is marginal, at best, on a larger displacement engine, especially one to be used in a performance mode.

Keep in mind, their "performance" engine was a 4.1 NON-TURBO. I would get the right crank.

 

[noslo6]

Ok, I think you've talked me into switching cranks. I'm gonna go to the machine shop that sold me this crank and slap his head. He knew what I was putting this in and he gave me a late model 3800 crank which I was stupid enough to have cryo'd. He had several cranks there that he was "calling" 4.1 cranks with rolled fillets. I'll go see if he's got another 10/10 crank and swap it out. It'll cost me $125 or so to re cryo. If I don't have to replace bearings, that'll be cheaper than the flexplate anyway and I'd feel safer too. Thank you guys for pointing me in the right direction. I tend to agree not knowing the exact balance of this crank and whatnot, it's just not worth it to throw away all the other goodies I rebuilt the engine with just to run this crank. I'll get the right crank. Thanks again guys for all the input. I'll let you know how it turns out. And also... sorry to hijack this guys post....it was just the same idea I was talking about.