Cih crankshafts

[moodoo]

Guys

Am about to start a 2.0 CIH build. I have 2 cranks, one with 4 balance weights, and one with 8. Both cranks weigh the same. Anyone know the difference, or why, or if there’s any reason why I should use one of them over the other?

[H-400]

I would check the stroke, my expierence the 2.4 has got the 8 counterweights. But there is something weird with your 8 counterweight crankshaft: The oil seal flywheel side are all the same size. Only the 2.3 Diesel, the "400" 16V and the 3.0-24V engines have a bigger one. (Dimensions look at my "400 repair" topic). But your cranckshaft has got at the flywheel side something like a pulley looking thing. The counterweights look also different, look at my 2.4 CIH cranckshaft:

[moodoo]

Thanks Herman, I think the flywheel end is standard, it just had the oil seal sitting on there. Unless you’ve seen something I missed? There is a part number on the 8-weight crank, but it doesn’t mean anything to me. Stroke of both cranks is the same, just around 70mm best I can measure, so likely 69.8.

[H-400]

Thats what I was looking at, the oil seal. So, it's for sure no diesel (2.0-2.1-2.3) crank, they have all 85mm stroke. Never seen it before a 2.0 petrol with 8 counterweights but I'v been looking at the German websites and they excist, but are very rare... 👍

[moodoo]

Thanks a lot Herman...so it's rare...but is it better? If I'm choosing which crank to use...I suppose the 8-weight one will be more stable, which is good, but will have more surface area chopping through the oil, which is not so good. I'm not building a race engine, just a slightly sport road one. I have seen mention on the OpelGT site of some cranks being cast, while others are forged. I don't suppose it's going to matter much for a road engine?

[H-400]

Copied this from a German website, described as an Opel Motorsport crankshaft. Think the stability of a well balanced engine is more important. And as you can see on your pic the counterweights of the top crank are bigger, so it will compensate. I would go for the 8 weights one, my "400" has also a 8 weights one and is nitrated from factory but think for a road engine it won't be required.

[Jessopia74]

I would go with lower rotational mass and get the whole bottom end balanced properly. (That’s rods & pistons matched) then send to ballance with crank/flywheel. 
 

 

[H-400]

Balanced and lightenend:

[Jessopia74]

1 hour ago, H-400 said:

Balanced and lightenend:

Very nice, looks like they was able to remove quite a bit when knife edge those counter weights 😎👍

[moodoo]

3 hours ago, Jessopia74 said:

I would go with lower rotational mass and get the whole bottom end balanced properly. (That’s rods & pistons matched) then send to ballance with crank/flywheel. 
 

 

Cranks are the same weight though? I would be inclined to go with the 8-weight one, probably won't make a difference for a road engine, but seems to make sense to use something which is likely more stable in rotation?

[Jessopia74]

8 minutes ago, moodoo said:

Cranks are the same weight though? I would be inclined to go with the 8-weight one, probably won't make a difference for a road engine, but seems to make sense to use something which is likely more stable in rotation?

That would make sense as it has less counterweights, but same balanced effect. but have you checked the weight?

Might be smoother, but not that you will notice much difference between the two. Again biggest gains would be from reducing the mass vie lightened and balanced bottom end 

Edited March 29, 2023 by Jessopia74

[moodoo]

yep, both cranks 17.7 kg strangely enough...!

[cam.in.head]

as far as i remember the cranks for a 1.6 were different .design wise to the 2.0 not that there would be a reason for it or that they were not interchangeable ? 

but im sure that the 1.6 cranks were more desirable for some reason ? ? 

[Irmscher Man]

If I remember correctly, the 8 counterweight cranks were found on the 1.6s and the 2.4 only. I think the early one is a cast crank too, and the later 2.4 ones are forged so that might influence what you want to do with it. I read that the reason Opel changed to the forged (and more expensive) crank may have been due to a higher than acceptable number of failures of the cast one.
The M400 crank is different again and not the same as the 2.3 diesel one, which I think is a bit of an urban myth.

I read on the OpelGT forum that some 8 weight 2.0 forged cranks are about but rare, and someone suggested they may have been fitted to some cars with auto transmission. Not sure if that’s true but it sounds feasible. 

I have new 1.6s and 2.4 cranks in the store, so I’ll have to dig them out and check the part numbers for you.

[moodoo]

Thanks for the feedback guys.

If it's any help, (or may add to the uncertainty!) the 8-weight crank came as part of a 'factory recon' 1.9 bottom end that I bought years ago. It was still sealed up, brand new and unused, 0.5 undersize bearings, and 0.5 oversize pistons. For that reason it would be my preference to use that crank, since I know it is 'new', as opposed to the other crank which is very definitely 2nd hand, although looks in good condition, all journals in good nick, and at original size.

[rutts]

As said the 1.6 crank has the 8 counter balance. If balanced with other rotating parts can be safely used upto 8000 rpm. (I know I had an engine with one fitted but a 1mm oversize 1.9. ) some tuners knife edge the weights too just to lower rotating mass.