I went and did a good amount of research today concerning putting 3.1 cranks in our Fiero's when rebuilding the engine.

Most have told to get the crank kit 10610 from Autozone. This crank is for the 3.1 DIS ignition which means it comes with an integral disk on the crank and was used in all front wheel drive cars. It has been said that this is the stronger 981 casting crank. THis is also a neutrally balanced crank from what I have been told and uses a neutral flexplate/flywheel

Well some of you might remember when GM put 3.1's in Firebirds. Well Autozone has a crank kit for this engine too and it doesn't have the integral disk on it. Kit number 10620. Amazingly it is also a 981 casting without the intregral disk for the DIS ignition cause the firebird used a distributor. This is not a neutrally balanced crank and needs a flexplate/flywheel that will balance this crank.

Many questions have come up about when using a 3.1 crank which flexplate/flywheel(f/f) to use. Well I don't have a part number from Autozone for the flywheel for the manual trannies cause I don't care about you manual tranny guys :O but for us auto guys I got some details

If you are going to use the Crank with the disk on it then you will need flexplate number FRA-138. I guess it is made/supplied by Pioneer and the cost is $38.99. If buying the crank the crank kit which includes the crank and the bearings for mains and rods will cost $138.99 which includes a $43 core. So most of us will have to bite the bullet and fork over the $43 for the core bringing it to $180 or abouts.

For those that don't want that integral disk then you can go with the Crank kit 10620 and get Flexplate number FRA-165. The fleplate is $39.99 for this one. Price for both crank kits are the same.

While I was there I checked to see about the starters and if the same ones were used for the 2.8 and 3.1. Guess what.... they are not. Apparently according to autozone the starters for our FWD 2.8's and 3.1's are different and after doing a visual inspection they are different. Looked to me that the throw on the Bendix drive was shorter for the 3.1. So my question is to people that have done the 3.1 conversion were you still able to use the 2.8 starter????? This is the first time I think this has come up about the starter thing. I haven't heard anything about it before but want to make sure just in case. ERIC or Greendano?? I am sure you guys could help.

Also I was wondering if anyone knew the weight difference between the DIS crank and the crank without that disk is. I would expect that the crank with the crank sensor wheel on it would weigh more then the one without it, i.e. the firebird crank. The Autozone guys said like 1 pound and it wouldn't be noticeable. However I don't believe them. It is a fairly large disk on the crank so I think it would add around 5 pounds or more easily. Anyone have a crank that has not been installed with this disk on it and want to weigh it? I will weigh my 2.8 crank and we can compare the differences. I know the 2.8 crank probably doesn't weigh the same as the 3.1 crank without the disk but I am sure they are damn close. Will I have to use a different harmonic balancer with this Firebird crank as it is balanced differently or is the 2.8 harmonic balancer nuetrally balanced?

Also anyone use the Firebird crank? I have thought about this one cause it should weigh less and get the revs up faster.

Just thought somepeople might like to know this info and also hoping someone can help me with my questions. Thanks

Shaun
85 Gt with nitrous
in the process of 3.1 but just need crank now.

I wish I knew what that "disk" you discribed looked like. As far as I know, my 88 2.8 crank looked exactly the same as the 3.1 crank. I bought the 3.1 crank new from GM. Unfortunatly, it was really expensive ($350) and may not yeild a significant advantage or any at all. I'm not sure what car/van it was used in originally, but it was the 981 casting I think and was balanced internally.

Fortunatly, I could retain my original flywheel, so there was no reason to go to a different starter. I just shelled out the $25 for a rebuilt starter for the 88 2.8. If the starters for the 88s are the same for the other years, there would be no reason why you couldn't use your starter. I know from experience not to go into an auto parts store and tell the sales clerk I have a 3.1. He'll look at you cross-eyed and say "What you talkn' bout?" I ordered a 3.1 waterpump from GM by accident. Of course it was completely wrong and I wasted a month trying to rectify the situation. At this point I just tell myself, it's just a 2.8 with a bigger crank.

Eric, the 88 2.8 crank was internally balanced just like the 3.1 so it had this disk as well. The pre 88 especially my 85 did not have this disk on the crank.

Could you give me the GM part number for the 3.1 crank that you bought? There were two 3.1 cranks made by GM. One was for FWD applications with DIS ignition which was also internally balanced and then the 3.1 crank for the Firebird which used a distributor. There are two different part nubmers and I have a GM catalog here that lists both part numbers for each crank. Actually the crank with the DIS crank disk on it is for the aluminum head engine of course it doesn't really matter. That is what the Gm catalog says anyway.

Can anybody else help?

I used the DIS ignition crank, firebird pistons&rings, and a 3.1 flywheel(used) in my '85 4spd. I used the same starter with out any trouble.

Squid, what about the balancer? For everyone here is what ed parks sent me about this issue when I asked him.

<<<we don't buy "hard parts" from Autozone. (Have friend that put 3 of their cranks in his 2.8 within 4 mos.) We also do not build engines so can't comment on the 2 3.1 different cranks. Remember that the 3.1 crank also requires 3.1 pistons.

The 2.8 starter will fit the 3.1 FWD engine.

Well, got one out of 3!!! (opps add 1 more...The harmonic balancers have
different part #'s between 87 and 88 Fiero engines but we have interchanged them OK) 3.1 balancer would have to have timing mark
reindexed like the 3.4. Otherwise timing mark comes up on wrong side of engine.>>>

Perhaps I should just shell out the $350 for a new crank. That would really cut into my budget for this project. I know think it would have been just easier to reuse my original 2.8 crank and save from all this hassle. Please tell me it is worth the extra hp and torque.

I really have no experience with Auto Zone cranks or which is better/worse (FWD crank or RWD), but I do know that all 3.1 V-6 cranks have the 981 casting number.

My personal opinion though is to use the neutrally balanced crank, whether or not the DIS disc thing adds a few pounds or not.

You may have talked about it and I didn't see it (Its late and Im about to go to bed) but the crank weight shouldn't be that much of a consideration as much as making sure that you have the correct flywheel for it. We had a customer come in and his car had this horrible vibration in it. He had a weighted flywheel on an 88 crank. The weights were for the unbalanced earlier cranks and were throwing his crank out of balance. No damage was caused but then he wasn't driving it for long. Good luck to you!

The GM crank is 10078981 lists for $530 and costs $389. It's up to you Shuan. This one might be a better crank, but I don't really know. I do think the extra displacement of the 3.1 is worth a little headache. Torque is vastly improved and with the big cam and all the porting I did to this motor, that's really saying something.

If you are going to order a new crank for the 3.1 conversion, order the GM 10146900. It is an updated version of the 981 crank with better balance characteristics

I used my original neutral harmonic balancer. I didnt have the assembly balanced but it runs very smooth at all rpms.Also, I used a crank kit from Advance auto parts.They looked it up for a '89 Pontiac 6000.