Lateral movement in crank shaft

[Jab458]

Hey all,

Recently did an engine rebuild on a ‘79 447 engine. It was a full top end job with a 1mm overbore, and I installed a crank from a donor engine since I found that the small ends of the existing one were beyond toast.

It’s been running great and obviously the top end job stuck, however I occasionally hear a good clunk from the case, especially when using the starter motor and it’s struggling to start.

I saw some threads about similar noises occurring when the alternator magnet wasn’t torqued properly so I removed the side covers to check torque. It’s got the 50-54 ft-lbs that is expected. I did find though that the the whole crank shaft has lateral movement, enough to make a clunk in the case. When I move it from the alternator side I find that the same movement happens on the clutch side, so I suspect the whole shaft is moving back and forth. I can only imagine this is not a good thing.

My question for you all: is this a symptom of main bearing failure? I’m going to go back through my photos taken during installation to see if I missed some washer that might prevent this.

Would love to hear some opinions, suggestions, and to be told I’m missing something obvious before I decide to tear the whole thing down and build a new crank for it.

Video of crank shaft moving linked below.

 

[Jab458]

A relevant point is that I didn’t consistently hear the knocking under normal load, making me think it’s not a normal rod knock

 

[Jab458]

Unfortunately I think I’ve found my issue in my build pictures. I’m believing I missed a shim or something. Gap is by feel about the same amount of play I’m feeling side to side. Good rookie mistake if so.

 

[Its been a long time]

Here's a section from the official shop manual. See how the main bearings locate on small locating pins to stop the outer race from being displaced? See the black arrows pointing at them in the picture? The shaft should not float laterally if it's built correctly.

 

[grouchie77]

Check to see that those little dowels pins haven't somehow fallen out, or sheared off. The bearings shouldn't be walking back and forth.

 

[Jab458]

I spent quite a while lining those up during assembly, and made sure they were rotationally mated prior to closing the cases. If that’s it I’ll be mildly upset lol.

Assuming the races are lined up correctly with the dowels, I can only logic that bearing failure or neglected shim could cause the slop.

I’m pretty sure at this point it’s pointing towards the cases need to be split again.

 

[Its been a long time]

Just how much end float is there? Have you measured it with a dial gauge or is it too much to measure?

Here's a picture of the assembly. I find it difficult to understand how it can float more than a few thousands without an alternator side bearing failure?

 

[Jab458]

Haven’t gotten a dial on it yet, but I’d say it’s roughly 1mm. Certainly greater than a few thou and enough that I can make it audibly clunk. I’ve been studying the assembly and I’m not convinced I missed anything. Found pics that indicated at least the left and right side bearings were lined up correctly, can’t cross check the middle two obviously.

I’ve got a spare crank and case that I’m going to poke with to see if I can somewhat replicate it. Other than that I think i am going to tear down again before my fresh cylinder bores are destroyed if they haven’t already been.

Thanks for the input!

 

[Its been a long time]

Haven’t gotten a dial on it yet, but I’d say it’s roughly 1mm. Certainly greater than a few thou and enough that I can make it audibly clunk. I’ve been studying the assembly and I’m not convinced I missed anything. Found pics that indicated at least the left and right side bearings were lined up correctly, can’t cross check the middle two obviously.

I’ve got a spare crank and case that I’m going to poke with to see if I can somewhat replicate it. Other than that I think i am going to tear down again before my fresh cylinder bores are destroyed if they haven’t already been.

Thanks for the input!

If it's a mm give or take, you don't need to measure it I would say. I was thinking maybe a few thou.

All I can really think of without seeing it is that the left side crank main bearing journal is seriously worn and the shaft is sliding through the bearing bore. You would have noticed a badly worn ball race when fitting the assembly, I'm sure.

 

[Jab458]

Always possible to have overlooked something I suppose. Will poke a bit further, and will update if I find anything interesting (or not)

 

[Miker Vee]

There are 3 roller bearings on the crankshaft, and 1 ball bearing.
The roller bearings are supposed to have axial play to allow the shaft to expand when heated.
The ball bearing (on the right side of the crankshaft) is what fixates the crankshaft in axial direction.
To do this, the outer ball bearing race is kept in place by a dowel pin.
If the dowel pin is missing, the ball bearing can slide axially, and the crankshaft with it.
Ball bearing is (15), dowel pin is (20) in the drawing below, grabbed from the CMSNL site.

 

[Jab458]

The dowel was certainly in place prior to crank shaft install. I guess I’ll remove the drive sprocket there and try to get eyes on that inner race, see if it is moving.

 

[dps650rider]

Is the crank moving within the inner race of the ball bearing?

Is the entire ball bearing moving in the case?

Is the ball bearing itself loose?

I had lateral play in the trans input shaft that was causing changes in clutch free play. This was caused by the groove in the case where the retaining ring fits getting loose (lots of miles on my cases). I fixed it using Loctite 620 retaining compound in the groove in the case. Did the same with the crank ball bearing too being careful it can't get into oil delivery holes. That was years ago and it's been fine ever since.

 

[dps650rider]

BTW, I believe the sole purpose of the dowel pins is to insure alignment with the oil delivery holes. The steel ring is there to prevent end to end movement.

And a little end play caused by the bearing itself is no big deal. I think there is a spec on it but I don't remember for sure.

 

[Miker Vee]

BTW, I believe the sole purpose of the dowel pins is to insure alignment with the oil delivery holes. The steel ring is there to prevent end to end movement.

And a little end play caused by the bearing itself is no big deal. I think there is a spec on it but I don't remember for sure.

You are right, sorry for the misinformation.
The clip is what keeps the ball bearing in place, axially.
Jab's picture clearly shows it in place.

 

[Jab458]

Inspecting the right side ball bearing, the outer race does not move (good!). I do see that the bearings themselves move, and it looks like the inner race moves with them. No more play that what I see moving there so I believe that’s the source of the side to side.

Going to hit it with a dial indicator at my next chance, if it’s a pretty small number (whatever that may be) I may just run it and keep an eye on it to see if it gets any worse going forward.

 

[Jab458]

Got to measuring it with a (cheap digital) dial indicator today. Seems like I’m over sensitive and overestimated the play.

Only 9 thou of axial movement on it. Going to check with a better dial when I get to it, but I expect a similar number.

Will be reassembling and getting back to riding.

Thanks for the input everyone!