Changing crank main bearings

Status
Not open for further replies.

SteveBorland

VIP MEMBER
Joined
Nov 15, 2010
Messages
777
Country flag
After my little incident with melted pistons at Spa this year, I decided to split the crankcases just to have a look inside. I was not going to do this since the crank felt fine, the cam and followers look great, what could possibly go wrong??? Hmm, what's that I see on the magnetic drain plug? Little shiny bits???? Where do those come from?

Anyway, the timing side main bearing inner race has some nasty spalling damage, so now I'm into changing both mains. I've ordered new bearings plus other stuff from RGM (they offer mains in C2 and C3 classes, so I chose the C3 bearings after doing quite a lot of reading.

As far as I can see, the outer races will come out simply by heating the cases. We have an industrial oven at work that will go up to 200 deg. C - is this hot enough?

The other thing I'm wondering about is the drive side inner race. These seem to be quite a tight fit, and I often see references to a special puller being used.
Generally I prefer to do as much work as possible myself (then I know who to look at when it goes wrong) but I don't see any point is spending quite a lot of money on a tool I will only use once.

I hope...

If this special puller is actually necessary, then I will probably hand the whole job over to a local mechanic who seems to be quite good at this sort of stuff.

Any views or comments on this?

I received my new JS pistons last week (hand carried to Ireland and then posted from there - it's amazing what we will do to avoid the dreaded tax man :). Pure mechanical porn, each packed in it's own little cloth bag. Almost too lovely to hide inside the engine, but at that price, there's no way I'm ordering another set as decoration!! Hopefully the extra 0.5mm between the valve recess & the rings will make it more robust, and more to the point, I will be paying much more attention to the mixture (as well as ensuring that the bloody manifold bolts do not loosen off this time!!!!!)

/Steve in Copenhagen
 
Hi Steve - bearings should drop out in 30 minutes or so in 400 degree Fahrenheit oven . Inner races are difficult to remove from mainshafts . Unless the last person to put them in had the forethought to grind a chamfer on the back , even getting a bearing separator behind is difficult. If you have access to an electric induction heater they work best as they concentrate the heat on the piece you are trying to expand whereas a torch heats everything. If you are not familiar with these they are a hand held device with different sets of cables that wrap around the piece requiring heat. You may have to shim behind new outer races to achieve proper end float in crank . Norton manual says .005” - .015” but others say more is acceptable. I found my replacement bearings to be .003” less in depth than the originals.
Hope this helps - RT
 
200C is enough for them to drop out under gravity, using a blow torch to heat a half case until spit sizzles works most times and that is lower than 200C.
 
Changing crank main bearings
 
Yes, you need a bearing separator and puller, BE CAREFUL!!
That is, if it’s really tight, (and mine was) the cone on the pusher screw could deform the end of the (drilled) crankshaft. When I felt it was really tight, I added an aluminum block to push on to avoid that. Propane torch directly on the race and it eventually gave way.
 
When you install the outer race in the case it only needs to be 200 - 220 degrees. Make sure the outer race is also warm do not put in the freezer. If it is cold from the freezer the case will start contracting IMMEDIATELY when the outer race touches it. Give yourself some time while trying to get the bearing in straight.
 
I put my cases over the wok burner on my gas stove and heat the case up that way it only takes a minute or two for the bearings to drop out then I flip them over and let the new bearing drop straight in then leave the cases to cool down, have done this many of times without problems, as for the inner bearing a puller is your best friend, I have always pulled them off cold even when tight, you think its never going to release but when it does in makes a big bang when they do, I then put some oil on the crank so the new inner bearings can be tapped on I use the old inner bearing to tap then on till hard up on the crank, I have been doing it this way for over 38 years on my Norton as well a few other mate's Norton's that I have rebuilt or helped with bearing removal.
You can never loose when it comes to investing in tools for your motor and a few different bearing pullers are a good investment if you intend in keeping your Norton, if you only use it once at lease you know you have it incase you need it again, you will always get your money back if you ever sell your puller.
Over 43 years of owning my Norton I have every tool that I need for my Norton in my workshop, having the right tool make life a lot easier when doing major engine or any other work and swap meets are a great place to build up your tool collection, if you are going to invest in your bike then invest in the right tools as well.

Ashley
 
Thanks for the quotes, but I'm running a Pazon at around 28 degrees, so I don't think excessive advance was involved, and anyway, this would not affect the crank at or near BDC.
Cannot really see a connection between this spalling and my over cooked pistons, even though it's tempting to conclude that. Don't really like coincidences...

On the other hand, I should be happy about only having to strip the motor once I suppose :)
 
htown16 said:
You need a bearing splitter to pull the inner race. Two clam shaped piece of metal with knife edges that wedge behind the race. In the states, auto parts stores loan them out. I would think most machine shops have them. I would'nt take the cases to 200 c, around 120 should do it. Give them a rap upside down on a block of wood.
https://www.amazon.com/Shankly-Bear...EK7HQBPFBF3&psc=1&refRID=3CNVTAEN8EK7HQBPFBF3
Click to expand...

I was thinking 120º C, too. At least to start, if they don't come easily, go another 20 or 25º and try again. 200º C probably won't hurt anything but why go hotter than you need to?
 
Last edited:
The barbeque method worked well for me, as photographed above. I actually bought a cheap clamshell puller for about $50 but could have rented one from a local automotive supply store (O'Reilly's I believe). I bought it since I plan to do at least one more Norton engine that is sitting on my shelf. It's worth checking end play I suppose (I checked mine) but when I browsed the threads here it seemed that the need for a shim was rare.
 
Status
Not open for further replies.
Back
Top