Topic: Crank Journal condition

[rugger81]

Inspecting my crank on a full rebuild. Looked pretty good at first to my untrained eye, but I went through it slowly 3-4 times and I caught 3 marks. More or less just wondering if I need to do anything about these, or if they aren't too bad and I can move on without worrying too much.

Starting with the deepest to the shallowest.




#1 No raised edges. Nail doesn't really clip on it, but if I feel around for it I can barely rest m



#2 clips my nail as I brush over it, but very shallow



#3 same as before but even more shallow


Lastly, my second rod bearing had a really nasty mark and scratch in it. Journal had a visible line but didn't feel like it made any indentation.





Took video as well if you're so inclined to see it all. Quality isn't good enough to show any marks really, but shows the whole thing.

thanks in advance

-Joe

[pjlogue]

It is hard to tell in some of the pictures if there is flaking towards the edges of the journals or if it is dirt/oil.  You should clean it well to remove dirt and oil and use a magnifier to really look at the journal surfaces.  Some pitting with no raised edges will be OK but if there is any flaking/galling, if it were me, I would seek a good replacement.  You should also take a mic to it carefully measure and make sure of diameters before you invest time in it.  If it is below min clearance for a shell match it is not worth putting time into it. 

-P.

[rugger81]

Sorry for the quick bump. I should admit this is the thing I'm most nervous about this whole project. I should temper my first post saying, each one just barely clips my fingernail. I need to really move and strain with the light to even see or get a good picture of things. Pictures are taken to in a way to highlight the marks as best as possible.

[rugger81]

It is hard to tell in some of the pictures if there is flaking towards the edges of the journals or if it is dirt/oil.  You should clean it well to remove dirt and oil and use a magnifier to really look at the journal surfaces.  Some pitting with no raised edges will be OK but if there is any flaking/galling, if it were me, I would seek a good replacement.  You should also take a mic to it carefully measure and make sure of diameters before you invest time in it.  If it is below min clearance for a shell match it is not worth putting time into it. 

-P.

you're right. I cleaned each off with a rag to inspect, but didn't take pictures until I re-oiled them. I'll clean them off a bit better and get better pictures.

Updated with clean pictures. Just noticed a lot of white specs from the cotton tshirt I wiped it down with.

#1

#2

#3

[TjTalan]

If that was my crank, I would replace it. it’s just not worth the risk in my opinion. 


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[754]

If its low spots , its likely ok.
 Was it parked long time, or run recently ?

 Here is what I suspect, acid in the oil. It forms a drop or spot  on the bearing,  in fact it seems to dissolve the bearing material.
I think it can form when the bike sits thru the winter.
 I had it happen on mine once, unaware of it I ran it and took out the crank early in the season. In fact I was in Calgary AB when it started knocking, tried to ride it the 375 miles home. 50 miles from home it was knocking all the time. Done..it in.
 Cranks are really cheap , but you need to buy bearings.. they cost more than a used crank.

 However if you tear a motor open, and find this and polish it up, i.e. no high spots, it would probably run for ever with a new bearing.

[bryanj]

Help to know what engine it is.
If no raised edges on any of the marks it will run and be ok for a stock motor but not a tuned or overbored one

[dave500]

itll be ok,just use some 1200 wet n dry and wrap a boot lace around it,sort of zig zag it back n forth a little,take off that sheen a little,the soft bearings are designed to embed break in material and trap it,sounds wrong but thats what it is.

[rugger81]

Sorry, it's a 77 750k that will be getting an 836 kit with a ported head and a webcam 63a. So definitely hot, but will be for street use and won't be setting it up to run higher than stock rpm.

I'm a bit torn as sourcing a new crank, it's hard to know the actual condition without seeing it in person. Used cranks go for $30 to $100 in varying condition. There are a few local ebay listings that I can pick up and inspect in person.

The other option may be cycle x. I don't know of any source of cranks that should be in good to great condition than them. I'm a little hesitant to spend the money, but I may end up going one of their stock weight balanced cranks. They run $200 with a swap, but I assume I'm going to have to add the expensive cost of shipping a crank. Has anyone gone through that process with cycle x?

thanks everyone who's weighed in

[754]

 Never hurts to have z spare crank at those prices..

[bryanj]

If you are doing that to your engine change the crank, if you intend to use standard rods get crank with rods which will save cost of end shells

[rugger81]

I agree that I likely do not want to go with my current crank. I am already set on getting all new bearing shells, so mismatched shells won't be something I need to worry about.

I looked at a local one that overall looked pretty good, and journals were within spec on the micrometer. I did catch two little marks though after inspecting all the journals. Two horizontal lines on different journals that did not catch on my fingernail. So they felt smooth, but were a visible indentation. Just a mm or two wide. Should I question any little marks like this or are they likely going to be imperfections you'd find on most spare cranks out in the wild?

I know I'm likely not going to get anything perfect short of going cycle-x. I'm going to check with them tomorrow, but honestly it might not be in the budget. Will likely need to make a decision on that.

[HondaMan]

Sorry, it's a 77 750k that will be getting an 836 kit with a ported head and a webcam 63a. So definitely hot, but will be for street use and won't be setting it up to run higher than stock rpm.

Well, with that cam it WILL be a higher-than-stock RPM engine, as that will be where the power resides. You'd probably be better off with the Megacycle 125-00 (or -04), IMHO, to keep the RPM closer to redline or below.

The heavier toque of those pistons will test the crank journals: otherwise I would vote for polishing it down at the holes and running it as-is, because I have seen worse with high miles on them anyway. But, they were also stock K3-K6 engines, which make less HP than the earlier and later ones, and at lower RPM they have more torque by a little bit.

[rugger81]

Sorry, it's a 77 750k that will be getting an 836 kit with a ported head and a webcam 63a. So definitely hot, but will be for street use and won't be setting it up to run higher than stock rpm.

Well, with that cam it WILL be a higher-than-stock RPM engine, as that will be where the power resides. You'd probably be better off with the Megacycle 125-00 (or -04), IMHO, to keep the RPM closer to redline or below.

The heavier toque of those pistons will test the crank journals: otherwise I would vote for polishing it down at the holes and running it as-is, because I have seen worse with high miles on them anyway. But, they were also stock K3-K6 engines, which make less HP than the earlier and later ones, and at lower RPM they have more torque by a little bit.

I actually did not think of that at all, but it makes sense. When I bought all my go fast parts a decade ago, the intention was for some semblance of increasing my red line. My head is setup for it with titanium retainers and hd springs. I have the F rod bolts too. Thing is though I don't have much else. I didn't go lightened crank and didn't go with carrillo rods. I figured I'd just be pushing my luck with trying take my redline somewhere north of stock.

I'll park my cam selection for now until I'm a little farther in the build. Got your book by the way, its my main resource at the moment. Got it when it first came out all those years ago. Really glad I picked it up.

I've settled on a cycle x crank by the way. Not planning on going lightened, but will go balanced. In my other automotive experiences, lightening drive line parts probably helps with racing applications, but hurts a bit in everyday drive/ride ability. Still have a bit of time to decide if I want to drop the extra $100 on a lightened crank, but I don't see it as worth it at the moment.