4.1 Crank and 3.8 Turbo Crank. Are they the same?
- Thread starter Tim Cucci
- Start date
Red Regal T
Senior Member
- Joined
- May 24, 2001
4.1 production crank is the same as 3.8 turbo crank.
Is that why crank questions dont get answers? The only answer I got was I dont understand the question! And before you say it,yes, I did a search and my question was not in there!!!! All I wanted to know was could the cranks become bent enough that the rod clearence could not be made tight enough? Because thats what the machine shop is telling me.
b4black
Well-Known Member
- Joined
- May 24, 2001
People may pass over crank topics because most questions have been asked and answered many times before.
I haven't heard any disscussion before about slightly bent cranks. In this case maybe not enough people have experience with this. Cranks broken in half - plenty of those with gruesome pictures of mortally wounded engines.
Eariler Carb/Turbo engines and 4.1 V6's use the same crank as SFI/Turbo engines. Some have a different size bolt for the balancer, but this isn't a problem from what I hear. There are only two types of production, 3.8 RWD cranks. Those with, and those without, the rolled rod journal fillets.
I haven't heard any disscussion before about slightly bent cranks. In this case maybe not enough people have experience with this. Cranks broken in half - plenty of those with gruesome pictures of mortally wounded engines.
Eariler Carb/Turbo engines and 4.1 V6's use the same crank as SFI/Turbo engines. Some have a different size bolt for the balancer, but this isn't a problem from what I hear. There are only two types of production, 3.8 RWD cranks. Those with, and those without, the rolled rod journal fillets.
O
OldGrayII
Guest
Strange?? All the 4.1 cranks I've ever seen ALL have the rolled fillets!!! Sounds like you better keep looking!!!!!
Steve Wood
Active Member
- Joined
- Jul 18, 2001
There are several people who will tell you that there is no problem in running a non turbo crank in an 11-12 sec car.
I am not one of those people. It's a gamble and it has been done. But you are putting a crankshaft in the engine that is weaker by design than the original and I think you are gambling thousands against a couple of hundred dollars more. Lousy odds, I will stick to roulette or craps where the odds are known.
I am not one of those people. It's a gamble and it has been done. But you are putting a crankshaft in the engine that is weaker by design than the original and I think you are gambling thousands against a couple of hundred dollars more. Lousy odds, I will stick to roulette or craps where the odds are known.
Steve Wood
Active Member
- Joined
- Jul 18, 2001
Instead of whining because no one answered it, you might post it to the top again and ask for help.
Now, I don't understand the question either.
Are you talking about rod to journal clearance or rod to rod side clearance?
Either way, I kinda doubt that a bent crank shaft is the culprit. I would think a bent shaft would cause a problem with the mains, not the rods...
You might go back to the machine shop and get a better explanation and have them physically show you. Then you can probably get some help.
b4black
Well-Known Member
- Joined
- May 24, 2001
It originally would have the rolled rod fillets, BUT if it was ever remanufactured (which is very likely) it will have what ever crank the remanufacturer had on top of the pile. Same for the heads. There no reason for them to do otherwise. A NA crank is more than plenty for a NA 4.1 V6. It's only us Turbo guys that are so picky.
Tim Cucci
Member
- Joined
- May 24, 2001
The 4.1 I was looking at must have been a remanufactured crank. I do think I recall while talking to the machinist it was said that the only thing my crank was good for was a core for remanufacturing and that it would not have a rolled fillet in the damaged area where the thrust bearing rubbed the side of the crank after remanufacturing. HMMM??? Did that make sense?
Anyway I guess I am still looking for a real crankshaft.
Anybody got one? Reasonable price?
I took my convertor (stock D5) to the tranny shop and they said just by looking that they see nothing wrong with it. I still would like to know why the thrust bearing wore out the crank? Maybe somthing got between the side of bearing and the crank? Anybody know?
Thanks
Tim
Anyway I guess I am still looking for a real crankshaft.
Anybody got one? Reasonable price?
I took my convertor (stock D5) to the tranny shop and they said just by looking that they see nothing wrong with it. I still would like to know why the thrust bearing wore out the crank? Maybe somthing got between the side of bearing and the crank? Anybody know?
Thanks
Tim
I have an 82 NA 3.8 shortblock, the crank was brand new from GM in 1983...the block was rebuilt late 83, and sat ever since, the crank is marked 877, are all 877 cranks "turbo" cranks....Im not exactly what to look for or what the "rolled" filets look like
Steve Wood
Active Member
- Joined
- Jul 18, 2001
Thanx Steve,
I have seen that pic before...to me it is to dark to see whats really going on, but I compared it to my crank, I cant say for sure, but I dont think mine as the rolled fillets....I tried to snap some pics of my crank with the dig. cam. but my battery just died.
EDIT: I didnt even see the pic on the front page, I guess I didnt let in load before I clicked on "1986-87 3.8 Turbo Crankshaft - Casting number ".....I believe my crank is a "turbo" crank, or as the rolled fillets....basically it is the small "machined" looking area just above were the rod bearing would ride on the journals correct?
I have seen that pic before...to me it is to dark to see whats really going on, but I compared it to my crank, I cant say for sure, but I dont think mine as the rolled fillets....I tried to snap some pics of my crank with the dig. cam. but my battery just died.
EDIT: I didnt even see the pic on the front page, I guess I didnt let in load before I clicked on "1986-87 3.8 Turbo Crankshaft - Casting number ".....I believe my crank is a "turbo" crank, or as the rolled fillets....basically it is the small "machined" looking area just above were the rod bearing would ride on the journals correct?
Steve Wood
Active Member
- Joined
- Jul 18, 2001
It will have rolled in grooves on each side of the journals as the picture tries to show...
b4black
Well-Known Member
- Joined
- May 24, 2001
You don't need pictures if the crank is out of the engine, Just look at the main journals. The main's fillets are rolled on every crank.
On a turbo crank, however, the rod journals are rolled as well. So the best way to tell is to compare the mains and the rod journals. If they don't look alike, it's a NA crank.
On a turbo crank, however, the rod journals are rolled as well. So the best way to tell is to compare the mains and the rod journals. If they don't look alike, it's a NA crank.
Sorry, Steve, but I dont think I was whining. And sorry for being a little ignorant on this subject. Thats why I was asking!! And as for bringing it to the top, I posted more on my own thread just to keep it at the top!!! I am a little frustrated at the machine shop, this sounds like something they just made up so they could take just a little more time!! Would you believe they've had the motor for over a year!!!! What they are saying(as far as I understand) is that where the rods attach to the crank is bent just a bit. I think they are talking about the peice along the rod. Which is why the cant get the tight clearence on the rods. They say its bent out just a bit. Ok, now you can see that I'm no machanic, but when I could find no account of this in a search I began to get a little worried. Hope this helped, cause I'm already confused!!!!!
Steve Wood
Active Member
- Joined
- Jul 18, 2001
No worries, and don't feel bad, I am still confused!
I have a feeling you may need another machine shop, but maybe not.
There are two basic clearances that must be checked. The first, and most discussed, is the difference between the size of the journal and the inner diameter of the big end of the rod when the bearings are installed and the rod cap torqued down.
The other clearance which we don't talk about very often but is also important is the clearance between the two rods that occupy the same journal.
You can have a bent crank but normally, I think, that causes the crank to run out of round as it lies in the mainbearings.
I don't think I have ever heard of a crank that was bent in a rod journal.
Maybe, it is time for a second opinion? A year is a long time to be in a machine shop. Of course, I do have a Camaro that has been in the paint shop for almost 13 months now........sigh........
Is there some one living in the vicinity that can help you?
I have a feeling you may need another machine shop, but maybe not.
There are two basic clearances that must be checked. The first, and most discussed, is the difference between the size of the journal and the inner diameter of the big end of the rod when the bearings are installed and the rod cap torqued down.
The other clearance which we don't talk about very often but is also important is the clearance between the two rods that occupy the same journal.
You can have a bent crank but normally, I think, that causes the crank to run out of round as it lies in the mainbearings.
I don't think I have ever heard of a crank that was bent in a rod journal.
Maybe, it is time for a second opinion? A year is a long time to be in a machine shop. Of course, I do have a Camaro that has been in the paint shop for almost 13 months now........sigh........
Is there some one living in the vicinity that can help you?