Crankshaft ball bearing clearances

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madsundaysurvivor
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Crankshaft ball bearing clearances

Post by madsundaysurvivor » Tue Feb 05, 2019 1:12 pm

I would want a video showing like fit the ball bearing in the shaft on my crank.
In first time they fit very hard for my oppinion and I needed a pull tool to fit they in the shafts. Then I have decided polish a bit with green scothbrite, and I get fit it by hand.
In my 2t racing engines I polish the shaft until the bearing fall by your own weight, for that the press in the inner ring don't do interference with the balls clearance in hot. This shortened the life of the shaft, this don't import to me because I change the crank of these engines sometimes.
I don't konw if in the b25s usually fit so hard and if I leave in hand-press fit (without appreciable clearance) I will have some problem by the use. The pourpose of the engine is running to high rpm 8500-9000
[youtube]https://www.youtube.com/watch?v=_SGnBEd5XJo[/youtube]
[youtubehttps://www.youtube.com/watch?v=jAD_ABZf9nc[/youtube]

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Last edited by madsundaysurvivor on Tue Feb 05, 2019 1:22 pm, edited 1 time in total.

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Re: Crankshaft ball bearing clearances

Post by kommando » Tue Feb 05, 2019 1:22 pm

On a B25 the bearing inner is forced inwards by the mainshaft nut on the driveside on to the crank side, so as long as the nut is loctitied then the inner should not fret on the journal if it has the right clearance. You need to check the timing side to check that the inner is pressed against the side of the crank. If this checks out then I relieve the mainshaft journal until I get a tight sliding fit, ie it will initially go on with hand pressure say 50% to 75% on but a light tap with a hammer gets the full 100% which is close to what you have got in your video. Its then easy to get off on next disassembly but not loose enough to fret.

But I do not run my engines at 8500 to 9000.
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Re: Crankshaft ball bearing clearances

Post by madsundaysurvivor » Wed Feb 06, 2019 3:33 pm

Effectively to fit all the run I need a little hit of hammer,
Whell :lol: 9000 rpm is my expectatition after a lot of modifications....we'll see what I really get

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Re: Crankshaft ball bearing clearances

Post by minetymenace » Wed Feb 06, 2019 5:56 pm

B25 engine at 9000rpm:
fireball-422746_1280.jpg
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Re: Crankshaft ball bearing clearances

Post by kommando » Wed Feb 06, 2019 8:18 pm

Been thinking some more, as you have relieved the timing side if you continue with two ball bearings then the timing side will fret as the timing side needs to float and is not clamped to the side of the crank. As the journal is now relieved to recover you need to fit a roller to the driveside and modify the crank to locate off the timing side and fit the spacer so the timing side crank nut presses down through the timing side ball bearing inner onto the side of the crank. The driveside can be relieved as the crank nut will presson the bearing inner which will float inside the roller bearing.

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Re: Crankshaft ball bearing clearances

Post by minetymenace » Wed Feb 06, 2019 10:35 pm

As per later B25s...
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Re: Crankshaft ball bearing clearances

Post by madsundaysurvivor » Thu Feb 07, 2019 10:13 am

I'm sorry I don't understand well you, surely by my language.
We propose to me transform my crank to later models, fix by nut in timing side and use a roller bearing in the drive side.
If I use two ball bearing, fixed in the drive side, and the timing side crank journal with hand-press fit in the inner bearing ring, and outer ring tight fit in the case.
Do You want tell me that journal slips in the inner ring of the timing side? And crank could run to different speed that the bearing?
I could use a bearing in this side with less internal clear (C2 f.examp) <201
My crank is dynamic balance to 8000 rpm, like my other racing cranks. I dont know the static factor balance now. I always trust in my industrial mechanic for this. The motorcycle is for short races (land speed races) not for road races

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Re: Crankshaft ball bearing clearances

Post by minetymenace » Thu Feb 07, 2019 10:37 am

I think you are good,
kommando wrote:if you continue with two ball bearings
the key is "if"....you are not. You are going for a roller on the drive side so I think all is OK.

No doubt kommando will confirm this...
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Re: Crankshaft ball bearing clearances

Post by kommando » Thu Feb 07, 2019 11:36 am

My Spanish (and all other languages including other versions of English ;) ) is non existent so I have the greatest respect to people who post on forums that do not use their native language. However it does mean confusion can appear and needs clarifying. Best to sort it out before the crank is inside the cases.

From a previous post,
Then will not use spacer, I prefer two ball bearings, in engines not for Street, many times I use C4 polyamide cage.

viewtopic.php?f=3&t=8156&p=77072#p77072

so not sure which way you plan to go.


My advice is that this 2 ball bearing option only works with the timing side ball interference fit being as it left the factory. This interference is the only protection against fretting as the crank floats inside the bearing inner, reduce the interference and you reduce the protection.

Now that the interference fit has been reduced then the best option is to change to the later roller driveside main and modify the crank to allow the timing side bearing inner to be trapped by the addition of the spacer as per 69 onwards engines. You can't use loctite to restore the interference fit as the crank moves every time it heats up and cools inside the bearing inner and will break the loctite bond.

Using a C2 internal clearance bearing will not give you greater interference of the bearing inner on the crank main journal.

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Re: Crankshaft ball bearing clearances

Post by madsundaysurvivor » Thu Feb 07, 2019 3:30 pm

Thank you for your advices and patience. Here (in my land) is hard to find someone to talk about 50's 60's british engines. My Friends racing with me on the past and now some have workshops, but they only have a lot of knowledge for racing about smokies 2T, or classics ducati and moto-guzzi, laverda to they don't like the british bikes, they think that I'm crazy for complicating my life with these bikes. They can not understand the feeling when I put the T120 to 170km/h :cool:


I understand that I made a mistake, when polish the shaft

Then now I have two opitons:

1-transform the crank to later models
2-Rebuild the left (timing side) crank journal to the Factory data, to get intererence fit (more money :roll: )

As I said I prefer both bearing in ball bearings, then possibly I incline by the second

I have careflully measure the shaft journal, and I could think that I'm in the middle between interference fit and slip fit
the size of the journal is 0,9837" (24,987mm)

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Re: Crankshaft ball bearing clearances

Post by kommando » Thu Feb 07, 2019 5:05 pm

Option 3 have the ball bearing inner copper plated to restore the fit leaving the shaft as is.

This is likely to be cheaper than option 2 if you have a local plating firm serving the local factories as their maintenance depts will use it on old machinery. The bearing is blanked off on the sides and the outer coated with varnish leaving only the inner ID to be copper plated.

Option 4 fit a roller bearing to the timing side with the inner located on the journal using loctite, the shaft and roller bearing inner will float within the roller element/outer and the loctite will not be strained.

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Re: Crankshaft ball bearing clearances

Post by madsundaysurvivor » Fri Feb 08, 2019 2:00 pm

thank you, two minds always think better than one :thumb
Today I will ask for cooper plate here..

About de other solution, I take note, I hadn't think in it, then I could fix the inner ring with loctite 648

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