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E: Engine Main bearings


SteveO

Well Known and Active Website User
VOC Member
Having finally got the oil pump fitted (see thread), I am now experiencing some difficulty getting the inner races of the mains into position. I'm assuming that they have to be driven down until they are hard against the ground face on the flywheel. Is this correct? Stevens says it is better if they are a light drive fit on the mainshafts and I am aware that when the engine is stripped they should remain on the shaft, but how light is light? Mine seem to be quite tight on the shaft. I have supported the crank in the Workmate in such a way that I am only drifting against the relevant flywheel rather than the whole bottom end assembly, so hopefully I won't be knocking the flywheels out of true. The drive side one is nearly down, but the timing side is quite difficult.
 

Bill Thomas

Well Known and Active Website User
VOC Member
They are not very tight as a norm, It's easy to tip a bearing and think they are too tight,
Maybe bring it off and start again, If it has a steel cage, It's easy to damage them,
When using a puller,
The large part of the cage should be outer most, If it's inner most and you put a puller on it , The cage will be damaged, The brass cage type was better.
There should be a raised bit on the flywheel, About 30 thou that the bearing touches, Some times it is worn, And that will affect getting the rods in the centre of the cylinders,
If it is too worn, You can buy a shim, It's the same shim that's used in the Twin gearbox.
 

stu spalding

Well Known and Active Website User
VOC Member
Make sure that the timing side bearing is shimmed out enough for the oil pump worm to trap it, ie the worm should be tight against the bearing, not the step in the shaft. This is best checked with a dummy inner race that has been lightly honed to a slip fit. Cheers, Stu.
 

Bill Thomas

Well Known and Active Website User
VOC Member
Thanks Stu, The raised bit is on both wheels but Yes it's the drive side that pulls the crank into alignment.
 

greg brillus

Well Known and Active Website User
VOC Member
Heat the inner roller race with an electric heat gun (like a hair dryer) with the bearing hanging on a punch held in a vice, then using some long nose pliers slip the bearing over the mainshaft and it should slip fully home very easily. You can use this method to remove bearings too although it will take some heating as the shaft will soak up some of the heat........saves any mechanical damage to the bearing.
 

MartynG

Well Known and Active Website User
VOC Member
Heat the inner roller race with an electric heat gun (like a hair dryer) with the bearing hanging on a punch held in a vice, then using some long nose pliers slip the bearing over the mainshaft and it should slip fully home very easily. You can use this method to remove bearings too although it will take some heating as the shaft will soak up some of the heat........saves any mechanical damage to the bearing.
The late Mr Binns advised that the easiest method to install them was to heat them in a pan of oil (old saucepan on the stove, bearing in the engine oil in the pan till the oil just starts to smoke) then lift the bearing out of the oil with long nose pliers and drop it into the shaft. Straight way put a sloppy for box spanner over the shaft with a weight as a press onto the top of the bearing centre to prevent any creep as the bearing cools.

BUT before you do that on the Drive side you must first determine what if any thickness shim you need between the bearing inner and the flywheel in order to centralise the conrod. See OVR edition 18 - in the OVR Archives
 

Bill Thomas

Well Known and Active Website User
VOC Member
Are your mainshafts new ?, If so check the size, If old and marked, Clean up with wet and dry.
Always check New Parts some are not spot on !!.
Knock on with a tube rather that a punch, In case it tips.
 

Vincent Brake

Well Known and Active Website User
VOC Member
Heat the inner roller race with an electric heat gun (like a hair dryer) with the bearing hanging on a punch held in a vice, then using some long nose pliers slip the bearing over the mainshaft and it should slip fully home very easily. You can use this method to remove bearings too although it will take some heating as the shaft will soak up some of the heat........saves any mechanical damage to the bearing.
And if not get the oxigen torch out.
 

tatty500

Well Known and Active Website User
Non-VOC Member
If you've just spent a million quid buying new mains, then it is important to treat them properly.


SKF and RHP instruct us not to heat a bearing to more tan 120C "or the bearing hardness will be affected"..... and"a naked flame should never be applied to bearing components".

When using an oil bath even it should be indirectly heated in a water bath.

Tatty
 

SteveO

Well Known and Active Website User
VOC Member
Yes Bill, new mainshafts. I've now driven the bearings on (not brutally!), I used an old Moto Guzzi fork leg that is a good fit on the bearing inner and over the shafts. Now for the next problem. In the photo attached, you can see a bright spot on the housing (where a liner has been fitted because the housing was damaged) and on the retaining screws for the bearing plates. This is where the big end pin itself, not the nut, is making contact. So what is the solution? A shim on the mainshaft behind the bearing seems most logical, however this may put the crank too far over (as Stu suggested, the oil pump worm is already up against the bearing, not the step in the shaft and this is without the timing side being shimmed). Haven't got as far as putting the cases together yet to check centrality (!) of the rods. Did have to source an oil scroll for the alloy spacer as my engine didn't have one!
 

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MartynG

Well Known and Active Website User
VOC Member
Yes Bill, new mainshafts. I've now driven the bearings on (not brutally!), I used an old Moto Guzzi fork leg that is a good fit on the bearing inner and over the shafts. Now for the next problem. In the photo attached, you can see a bright spot on the housing (where a liner has been fitted because the housing was damaged) and on the retaining screws for the bearing plates. This is where the big end pin itself, not the nut, is making contact. So what is the solution? A shim on the mainshaft behind the bearing seems most logical, however this may put the crank too far over (as Stu suggested, the oil pump worm is already up against the bearing, not the step in the shaft and this is without the timing side being shimmed). Haven't got as far as putting the cases together yet to check centrality (!) of the rods. Did have to source an oil scroll for the alloy spacer as my engine didn't have one!
Your upcoming problem is REMOVAL of the new bearing from the mainshaft on the driving side so you can centralize the rods.

As I said earlier before you do that on the Drive side you must first determine what if any thickness shim you need between the bearing inner and the flywheel in order to centralise the conrod. See OVR edition 18 - in the OVR Archives for details on exactly how to do this - you will need the inner of an old main bearing to make a measurement spacer - that edition is in the OVR archives here https://ovr270.wixsite.com/ozvincentreview . All shims MUST be placed between the flywheel face and the bearing

Martyn
 

Bill Thomas

Well Known and Active Website User
VOC Member
The problem might be getting the bearing off to put a shim behind ?, Hope not.
If the mainshaft was too big, It needed making smaller.
Some people use a chisel, Just to get it away from the wheel, I don't like that.
With the old brass cage you could get the puller to rest on the inner of the rollers, And pull the bearing off.

Wish you had an arrow to show the mark, Like Bruce does !, I can't do that !.
Do you mean the mark high up ?.
Also looks like something is rubbing on the screws ?, I hate that fitting.
As you say it looks like it will need a shim behind the drive side inner bearing
But you really need to see if the conrods are in the middle.
I wonder if you have a Big Pin Bigend, That sticks out more than the standard one,
I had this years ago, When I laid the Bike over to the left the Pin hit the C/C wall, Felt like the end of the world,
I was Racing at the time !!. People said I was a bit Slow, A, Richard !!.
When George Brown fitted me a Big Pin, Many years ago, He ground off both the bits of Pin that was sticking out, That's what I would do next time, But you have to do little at a time, With an angel grinder, So as not to over heat the Pin !!
Not sure you understand what Stu was saying, I think Stu ment , The Worm must be out wider than the step,
So that every thing is nipped up, See what other people say, It's a bit tricky.
 

Bill Thomas

Well Known and Active Website User
VOC Member
Have you remembered to put the small Oil scroll on the shaft, The bit that fits inside that big alloy disc
Between the 2 drive side bearings ?.
Sorry I can see it now.
Can you give us a photo of the crank pin and nuts.
 

SteveO

Well Known and Active Website User
VOC Member
Bill, yes I thought the oil scroll was going to fix the problem. As I said above, my engine actually lacked this part. But it's made no difference. I appreciate that I need to centralise the rods, but there seemed little point in moving on to this before I got the crank turning without banging into something! I have had a mail conversation with Davidd on here and he suggests a cheap bearing seperator, ground to fit, to start the bearing off the shaft, so that is my next purchase. My thinking now is that since I probably need to shim the bearing to get clearance anyway, I am going to have to go with whatever that takes and hope the rods line up. I have to get the drive side free turning, as that is the side that is tightened up against pulling the crank over, not the timing side. I don't like the fitting on the main much myself, it is horrible, but I'm stuck with it unless I either scrap the case for a modern replacement or undertake major machining work that I can't do myself. I do have some F1 contacts and an engineer friend who told me that TZ750 Yamahas were raced in the Island with the bearings glued in with Loctite. I dont intend to use the bike THAT hard! In the meantime here are some photos of the crank. I am starting to wonder where this build is going as every time I fix one problem another crops up; it's beginning to get me down if the truth be told...
 

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Bill Thomas

Well Known and Active Website User
VOC Member
Chin Up Steve, Just think how good you will feel if you can sort it all out.
If it was easy every body would be doing it.
As a rule the raised bit on the flywheel is about 30 thou.
If it's not worn down because of inner bearing spinning on the shaft before.
As I thought you have a big crank pin and nuts, I don't know why they make them like that,
Mine stuck out even more than yours !!
Have a read up on what Martyn says.
If its just the pin that is touching, As I said you can grind a bit off, Which is why I said you should find where the conrods are, If in the middle ?.
And looking forward, Check on where the oil hole is in the barrel liner, It wants to be below the bottom of the lower oil ring
 

SteveO

Well Known and Active Website User
VOC Member
Right, I've read the OVR archive article. I have the perfect start for a bearing spacer - the old bearings! Job 1 is get the new bearing off the drive side and start again. I'll check where the conrods are. If they do need shimming and I'm pretty sure that they will, hopefully this will kill two birds with one stone!
 

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