Crankshaft interchangeable ??

[gaffer77]

Hi can anybody tell me if your crank is knackered ,can you simply put a different one in from another engine??

I have heard in the past that the crank and engine cases were machined to fit each other on the production line so you won't be able to just swap for another crank ??

Also if you can fit a different crank is there a difference between years models ??

Thanx

Gaffer

[TopCatGr58]

Not getting Shafted!

Hey Gaffer,

I remember doing some research on this, and ALL of the crankshafts are the same, from 78E thru XJ! What is different is the sizing for the bearings. There are markings on the cases, and there are markings on the crank shaft, you compare them, do some subtracting of some sort and you are able to determine what size bearings you need to get the NEW shaft to match/fit with the OLD Cases!

I believe John as well as several others have had experience in splitting their cases and replacing the bearings, and can either correct or add to what I've said!
T.C.

[John]

Yeah you can, but you will probably have to replace all of the bearings, mains and rods.

[Geezer]

The cases are all bored the same but there is a small difference in the bearings and there was a code number on the end of the part number on standard bearings for the different sizes.

Geezer

[gaffer77]

Thanx for that !! now then can you still get all the sizes of bearings??

If not ,i know it's bad practice and hardly worth the effort but could you IF YOU GET STUCK !! just swap the crank and everything from one case to another??

Reason i ask is i got another bottom end but its been down the road BADLY bashed!!!

[Geezer]

Originally posted by gaffer77
Thanx for that !! now then can you still get all the sizes of bearings??

If not ,i know it's bad practice and hardly worth the effort but could you IF YOU GET STUCK !! just swap the crank and everything from one case to another??

Reason i ask is i got another bottom end but its been down the road BADLY bashed!!!

In theory yes you could move the whole set over but I'd check all the clearances with Plastigage before buttoning it all up.

Geezer

[John]

The crank mains in the crankcase are lined bored and matched to each other. By mixing crank case halves you may have a journal or two that are not the same diameter, and therefore the bearing sizing procedure would not work. IE..if #1 main journal is a # 3 size on one engine and the donor engine has a #2 sized journal, then those two case halves will have different sized journals on the same cylinder. Confused yet? It would be best to get a complete crankcase. The journal sizes are stamped on one half of the case only. It would be possible to do it if you keep track what size journal each case has, and size each case half independent of each other. That way you may have a brown and blue color bearing needed for the same journal, and so on. It could be done, I would think. I haven't heard of anyone doing it though.

[Geezer]

I don't think any one was sugesting mix matching case halve but rather moving a crankshaft and all bearings from one case to another.

Geezer

[John]

That wouldn't work either as the main bearings may not be a correct fit to the bearing saddles. That would take doing the math, and getting the correct size bearings.

[Geezer]

That's why I recommended using plasticgage to check clearances. I’ve replaced several cranks while working at various Yamaha dealers and I’ve never seen a single crank bearing sized by the outside measurements.

I’d bet my bottom dollar that the clearances would be the same after swapping the crank and bearings from one case to another.

Geezer