Fish's 1992 750C Engine Rebuild and Other Goodies

[ZoneAdmin]

The engine looks great.

Good luck with the knee.

[Fishrider]

Surgery went well. Thank you. I ran into one of the many problems I will have today. I realized that I somehow only have 5 bearing shells for my crankshaft. I think they are marked blue, but I have no idea which bearings they belonged to. I think I may have not pulled out the bearing shells from one of the halves, and I didn't save the order. Unfortunately, that crankcase is gone. Can I re-use the 5 bearing shells I have (marked blue, I am pretty sure) and order 5 blue marked shells, or should I order all 10 (expensive). I don't have the best calipers, but from what I can tell I think the bearings meet blue shell specifications, and there are no marks on the outside of the crank case. Although this crankcase is from a kz750.

TIA

Crankshaft

[Freddy]

What I would do is first is confirm that 'blue' main bearings are the correct size. Use the 5 you have to check the clearances across all the journals moving them around keeping one set at an appreciate end to best support the shaft. Use an appropriate range 'plastiguage' (available at any decent professional car parts place) to measure the clearances.

Then if you've determined that 'blue' gets the required spec, as you've mixed them up, using a new crankcase, and all the work you've done, etc. bite the bullet and purchase a full set of new bearing shells.

Before ordering, check the clearances on all the con-rod bearings using the same plastiguage measuring method. Replace if out of spec, surface scratched, or any sign of visible wear.

[DaftRusty]

As i'm sure you are aware, the bearing color codes (thicknesses) are determined by the bore in the cases and the crank journal sizes.
Kawasaki would measure the journals on the crank and stamped specific markings into the crank webs to denote size. (not all the journals would be exactly the same size, so each journal may have a different marking)
Then they also measured the bore size of the cases and then would mark the case as well. You are supposed to use the chart of marking codes in the manual to compare the marks on the crank with the marks on the case to determine each journal bearing color.
Since you are using a different case, you cannot reuse your old bearings!! The old bearings are "worn in" to the specific peculiarities of the old case bores, and will likely cause catastrophic failure if reused in the new case!

Chart

[Fishrider]

Thanks, for the input guys. I am going to do what Freddy said, and I'll check all the journal clearances with the bearings I have and see where I stand. The chart indicates shell color based on marks on the case and on the journals which there are none. I gather that as long as the diameter of the journal is within standard specs and there is no mark than I would choose blue shells no matter what. I would only choose black or brown if the journal diameters were within a lessor range, but as near as I can tell the journals are right at 36mm (although my calipers are suspect since they do not read at .001mm resolution). I did re-read the manual again, and it does say to replace all the journals at the same time if any journal needs replacing. This crank had less than 3600 miles on it. My guess is that it meets blue shell spec, but I will make sure. My only sticking point is that I do not have the ability to measure the inside of the case diameters which needs a .001mm resolution micrometer. My calipers just are not good enough to get an accurate reading. Again, there are no marks on the case so I hope that they are within standard spec. My hope is that the clearance once measured will be in within blue shell spec and I won't have to go any further. I would have to take the case somewhere to get proper measurements if need be.

[DaftRusty]

You are correct, If the case has no markings and the crank has no markings, then a blue shell is used.
Blue shell thickness- 1.498~1.502mm thickness

I also should have congratulated you on the progress you are making!
Keep up the good work!

[Freddy]

My guess is that it meets blue shell spec, but I will make sure. My only sticking point is that I do not have the ability to measure the inside of the case diameters which needs a .001mm resolution micrometer. My calipers just are not good enough to get an accurate reading. Again, there are no marks on the case so I hope that they are within standard spec. My hope is that the clearance once measured will be in within blue shell spec and I won't have to go any further. I would have to take the case somewhere to get proper measurements if need be.

Not convinced on the absolute need for a micrometer. Yes you would use a high quality micrometer as the only way to make sure the crank journals are not out of round. But with less than 4000 miles on it safe to assume they are not. To measure the installed clearance of both main and con rod bearings, 'plastiguage' is inexpensive and when used correctly more than accurate enough for a street engine. I take it your not building a race engine. The spec for the mains is 0.020 - 0.044mm clearance and that is right in the slot for the green plastiguage.

Just use the plastiguage to determine if blue bearings are not to tight i.e less than 0.020mm. Only if it fails that test would I worry about greater precision measurement as the other 2 bearing sizes are actually a looser fit.

If still in doubt regarding the accuracy of plastiguage, a pretty good test ..... https://www.youtube.com/watch?v=TBWC_1LVXUY

[Fishrider]

Help me work through this. Here are three of the journals. I did test the other two but forgot to take pics. They were similar to the measurements in the bottom two pics. I used the 5 bearings I currently have which I think are blue. I am fairly certain there are no marks on the crank shaft or case, and I really can't measure with any accuracy the journal or inside case diameters. The outside measurement was within standard, but the other two seem to be greater than .044. Assuming these were blue shells do I even have another choice other than to just go with new blue shells? The manual does say you can exceed the standard slightly. Thanks guys.

[Freddy]

Go to page 7-4 of your workshop manual. Two thirds the way down the page it lists the thickness of the 3 main bearing options. As you see the Blue option is the thickest, so will give the tightest clearance. So basically you have no other practical option than to buy 10 new Blue main bearing halves. Your old ones will be worn, so the new ones should result in a slightly closer fit which hopefully will fall within the 0.020 - 0.044 mm specification. Be sure to confirm the fit of all new bearings.

If it is still on the larger side or just slightly over, bolt it together, use a one grade heavier oil than you might normally and sleep well. You really have no other practical options anyway. No doubt someone can make special size custom bearing shells but as your not building a MotoGP engine that would be extreme. It's actually the con rod clearances that are more critical. I can't recall ever seeing a main bearing failure, broken crankshafts yes, and plenty of con rods that have hammered out the bearing completely.

[Fishrider]

Rod journal measurements were spot on. No issues there. I just need a handful of parts to close up the bottom. Won't be until the middle of July though. Hopefully, I don't run into too many more issues with buttoning up the bottom. No guarantees.

I found a guy to machine my clutch hub for the shorter input shaft. I had one question before I go milling out a perfectly good clutch hub. Does it matter that I will lose about 5-6mm of surface area on the clutch spring pusher that sits in the shaft? It seems the set up is slightly different on the Kz750 Daftrusty did. I wasn't sure whether the shorter input shaft made a difference for the pusher on that set up. I assume not. It seems that the pusher still has plenty of bar inside the shaft. So I am guessing that won't be an issue. However, The pusher does fall into the hub a bit far with the short output shaft. I feel like the clutch release rod may not be able to find the pusher if it falls in during assembly. Not a thing? I don't know if Brewmaster finished his swap. I would be interested to know if he ran into any other issues.

Edit: Could I just shim it with a couple more washers or some sort of bushing?

BTW, I don't think I would have attempted the swap without Daftrusty's fine manual on kzrider.com. Super job!