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6 May 2019
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Crank spins a little less freely after torquing primary gear
Hi all,
Still busy with my 3AJ project.
I replaced all the bearings, put new 4th and 5th gear and sent the crank to be balanced.
This month I put the crank halves back together and installed the primary gear, crank balancer gear, oil pump and clutch hub.
At this point, the crank moves pretty much effortlessly. It falls and rotates under its own weight.
However this week, after torquing up the primary gear nut to 120nm I've noticed the crank doesn't move as effortlessly as before.
It doesn't bind or grind. It feels smooth and there are no weird sounds. However it doesn't fall under its own weight anymore. When I stop turning the crank, it doesn't move back & forth anymore.. it just stops (if that makes any sense).
It's still relatively easy to turn (although slightly harder than before), I can crank it with 2 fingers by rotating the clutch hub no problem.
Is this normal? I checked for clearance between the bearing and crank and everything seems fine.
I didn't forget any spacers (triple checked).
Thanks!
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7 May 2019
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No thats not normal it should turn very freely and crank should turn under its own weight . I recently rebuilt a 3TB engine and when tightening up the crankcase halves together the crank became hard to turn. I found this was due to the crank bearing not fully seating into position onto the crank. It took a few hits on the inner race of the crank bearing while the crankcase halves still bolted together to fully seat bearing and it then turned freely. It wont spin freely with clutch basket and oil pump installed though due to drag of oil pump.
Last edited by dzl; 7 May 2019 at 04:25.
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7 May 2019
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Quote:
Originally Posted by dzl
No thats not normal it should turn very freely and crank should turn under its own weight . I recently rebuilt a 3TB engine and when tightening up the crankcase halves together the crank became hard to turn. I found this was due to the crank bearing not fully seating into position onto the crank. It took a few hits on the inner race of the crank bearing while the crankcase halves still bolted together to fully seat bearing and it then turned freely. It wont spin freely with clutch basket and oil pump installed though due to drag of oil pump.
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Hm.. but I'm quite sure the bearings are fully seated since I heated the crankhalves in the oven and the bearing/crank dropped in like butter with a satisfying metal sound hitting the end.
Also, just to be clear: it turned very freely before, with crank halves bolts torqued up. It fell/turned from its own weight. Even with oil pump and hub installed it was 100% freely turning. It wasn't until I torqued the primary gear nut that it became more resistive.
I made a video before torquing the primary gear (also with oil pump/hub). You can clearly see on the video that when I let go of the crank, it wobbles left/right before coming to a stop (no resistance).
Now, it just stops without wobbling. It's hard to explain because it doesn't feel like it's binding but it's just turns with slightly more resistance.
I'll make an after video and post them both later this evening.
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7 May 2019
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Hi....just a theory...Did you split the crank to change the rod or is it original? crank width checked at 75.00 mm? If the crank width was slightly below spec and when you tighten the primary gear nut you would be putting pressure on the inner race of the crank bearing if the outer race was unable to move with it as is a very firm fit in the crank case. The very slight misalignment between the inner/ outer races causing the slight binding?
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7 May 2019
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Quote:
Originally Posted by dzl
Hi....just a theory...Did you split the crank to change the rod or is it original? crank width checked at 75.00 mm? If the crank width was slightly below spec and when you tighten the primary gear nut you would be putting pressure on the inner race of the crank bearing if the outer race was unable to move with it as is a very firm fit in the crank case. The very slight misalignment between the inner/ outer races causing the slight binding?
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It's the original rod but I had it pressed. It had 0.90mm big-end side clearance and it was 75.30mm wide. I wanted it pressed to 0.60mm and 75.00mm (-30mm) but the shop couldn't get it that precise so it ended up being 0.50mm and 74.90mm width. So yeah, it's 0.1mm off from 75.00mm.
I guess your theory could be true. My understanding is indeed that it pulls the crank towards the primary gear until it touches the inner race of the bearing.
However isn't that the case regardless of crank width? If your crank is less wide, it will just pull it further. The actuall crank should move in its entirety away from the fly-wheel side. On the fly-wheel side the crank axle will just pull out of the bearing as long as you have room between the bearing and timing gear.
Maybe loosen it and apply 110nm with extra loctite just te be safe? Unfortunately I already bent the new tabs...
Maybe loosen the crank bolts and tap somewhere with mallet?
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7 May 2019
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the manual states 74.95 to 75.00 width but I had a crank that was out of that spec with no bad result although dont remember if it was more or less than the spec. I suppose it all depends on how tight the crank sits within its bearings both inner and outer races as to how it can align itself with in the crankcase on the bench. Engine in the oven and warm it up give it a hit either end of crank and will probably sort it out??
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7 May 2019
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Quote:
Originally Posted by dzl
the manual states 74.95 to 75.00 width but I had a crank that was out of that spec with no bad result although dont remember if it was more or less than the spec. I suppose it all depends on how tight the crank sits within its bearings both inner and outer races as to how it can align itself with in the crankcase on the bench. Engine in the oven and warm it up give it a hit either end of crank and will probably sort it out??
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I don't think it should cause too much problems except that you have extra clearance on the flywheel side of the engine.
Unfortunately with the cases back together it doens't fit into my oven..
I might loosen the crank case bolts and see what happens.
Otherwise I'll get the nut off and put it to 110NM.
The problem is that I don't know how it should be. The crank is definitely "free". Just less free as before..
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7 May 2019
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Quote:
Originally Posted by Doubleyoupee
I don't think it should cause too much problems except that you have extra clearance on the flywheel side of the engine.
Unfortunately with the cases back together it doens't fit into my oven..
I might loosen the crank case bolts and see what happens.
Otherwise I'll get the nut off and put it to 110NM.
The problem is that I don't know how it should be. The crank is definitely "free". Just less free as before..
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the clearance shouldnt be a problem but can the flywheel side bearing move laterally at all? They are usually very tight in crankcase and inner race is locked onto crank very tight also? Need to heat the crankcase so that bearing outer race can easily move that tiny amount to where it needs to be? I would give the crank bolt on the flywheel side a good wack even cold and might just move it as thats the direction the whole crank needs to go. Once the engine gets running and hot it will probably sort itself out anyway!
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7 May 2019
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Quote:
Originally Posted by dzl
the clearance shouldnt be a problem but can the flywheel side bearing move laterally at all? They are usually very tight in crankcase and inner race is locked onto crank very tight also? Need to heat the crankcase so that bearing outer race can easily move that tiny amount to where it needs to be? I would give the crank bolt on the flywheel side a good wack even cold and might just move it as thats the direction the whole crank needs to go. Once the engine gets running and hot it will probably sort itself out anyway!
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The inner race is not tight at all.
You can see here how easy it is to remove. Everything is cold here (video/gif):
https://imgur.com/CYRpFHf
It is however very tight in the crankcase, yes. That's why the crank should move towards the primary gear while the bearings sit solid in the crank case halves.
Yes, it might sort it self when engine is up to temp...
Whether I want to take that risk is the question.
Last edited by Doubleyoupee; 13 May 2019 at 09:22.
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8 May 2019
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yeah doesnt seem right. Going by your video of you removing the bearing on the flywheel side does the cam gear stop that bearing from moving at all on the inner race in the direction it needs to go? Does the cam gear butt up hard against that bearing?
Im out of ideas! Is very annoying having to pull engines apart again to sort issues. Have had to do a couple times!
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8 May 2019
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Quote:
Originally Posted by dzl
yeah doesnt seem right. Going by your video of you removing the bearing on the flywheel side does the cam gear stop that bearing from moving at all on the inner race in the direction it needs to go? Does the cam gear butt up hard against that bearing?
Im out of ideas! Is very annoying having to pull engines apart again to sort issues. Have had to do a couple times!
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I made sure to check that. There's still space between the bearing and the timing gear. Weirdly enough, it looks pretty much in the same position as before.
I know this because I painstakingly put the timing gear back at the exact same position after changing the bearing.
Maybe something is stuck and the crank is not moving... causing tension on the entire crank.
I also noticed the balancer weight not being exactly in the middle....
Even though it feels smooth otherwise I think I'm gonna loosen the crank bolts + some mallet tapping and see what happens. I read somewhere that this fixed it for someone with the same issue.
If nothing works I'll remove the nut. Gonna order another locker tab just in case. Thanks
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8 May 2019
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So this evening I loosened all the crank bolts.. no change.
I gave it some light taps but didn't dare to hit harder. No difference.
So I decided to loosen the primary gear nut again and immediataly it's super smooth again. Almost does half a turn from it's own weight even with hub and oilpump still attached.
Now to figure out how to torque it without issues.
I'm thinking of using the impact gun to initially tighten it, as that should pull the crank more straight since it's not bending the crank from all the pressure.
Then after I might set to 110nm on the torque wrench.
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12 May 2019
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Problem fixed!!
First I tried the impact gun to see if that would solve it.
Unfortunately after only a slight torque there was already more resistance.
This time I made sure to watch the timing-gear side to see if it was moving at all. And as I suspected, there was 0 movement.
So similar to what @dzl said, when applying 120nm, it probably pulled the inside of the bearing away from the outer race of the bearing instead of the axle moving and the entire bearing staying stationary.
This gave me the idea to try this
I will just push the axle through  . The bearing should be MUCH tighter so..
I only applied a little force and immediately *tick* I heard the crank move. I checked the timing gear and yep - less clearance to the bearing, the crank moved.
I then started torquing the primary nut while keeping pressure from the other side - just incase.
Nut is now torqued to ~115-120nm and crank is 100% as smooth as before:
https://i.imgur.com/2gkz2TI.gifv
So to anyone who finds this thread: YES the crank should be 100% as smooth as before torquing the nut. And yes it should fall under its own weight. Thanks dzl for putting me on the right track.
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13 May 2019
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Top stuff...I like a happy ending. Will keep that in the memory bank!
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Crank spins a little less freely after torquing primary gear
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