Tight crank bearing

Information relating to the Matchless G9 or AJS Model 20 500cc twin
theEagle
Posts: 16
Joined: Thu Jul 27, 2017 2:18 pm
Location: CHESHIRE UK

Tight crank bearing

Post by theEagle »

Hi,
I start with the question and for those interested I add a bit of introduction of myself below. So my first question on the forum:

I started to assemble the crankcase of my G9 53/54 by putting the crankshaft into the drive side, loosely fastening the web (as instructions here on the forum ) and then pre-mounting the timing halve of the case. However, it do not want to fit. (I realized here that the reason for needing to drive the halves apart when dismantling was not from sticky gasket sealant and tight fit of the centre web, it is the timing side bearing fitting too tight in the outer races..). The bearing on the timing side of the crankshaft does not fit into the outer race in the timing side case.
I have searched the internet on how to handle this but I am still very unsure (as this is far beyond my comfort zone). Some questions:
1. Should I be expected to need to heat up the case to fit this bearing?(not to fit the outer race in the case, but to fit the bearing into the outer race)
2. Why would it be too tight, any common reasons? (it is now viciously centre-punched in place by massive marks approx. 10*2 mm, 0.5-1mm deep.. !! , could this be the reason for it to become tight?)
3. Before I took it apart the crank turned relatively easy, can I just heat up the case and put it together? (ignoring that it will be hell again to take it apart…). This will probably make the procedure with pre-fitting to align the centre web not possible..
4. Would a new bearing improve the situation?
5. How the heck can I get the outer race out of the case if I want to??There are no edges to grip it.
6. Could just removing the centre punch marks (how??), extracting the outer race (if possible) , and then refit the race with less centre punches help?

I apologize for the lengthy text. However, I still hope you can come with some thoughts and ideas on this. I am new to this so I probably missed out on detail, but I am happy to provide photos and further details.

Kind regards and glad to be in the forum! :)
eagle
ps pre-apologizing for newbi forum misstakes as well as lacking terminology...and experience and....ds
------------------------- intro---------------------------------------------------
Hi everyone on the forum! Just registered, read a lot the last few month, found the massive archive, founds loads of valuable input already…finally taking the step to ask for help.

Short intro of myself: Lifelong whish to ride motorbikes, but still no licence…(now in progress). Some weird ( source unknown ) liking of old motorbikes particularly British ones. Like to understand how they work. Last 2 year dissassembled my Honda (owned for 25yrs) down to frame (removed cyl + top, but did not split case) and managed to get it to run after assembly again.

Current time: Stumbled across (looking at ads every day for 2yrs..) a Matchless G9 Clubman from 53/54. Most of it in one (rusty) piece , but engine in boxes. Realized that I stepped into the deep end by buying one in pieces (I had promised myself not to buy one in pieces. If I dismantle something I usually can sort it out. But now..) but I could not resist ….

So, now I have a puzzle since some month ago. I have managed to sort a lot of the pieces correctly(I think..). I started to split the crankcase that was put together but looked dirty (which it was). Here the problems started I realized now when I started to put it together…see top.
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Duncan
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Location: HAMPSHIRE UK

Re: Tight crank bearing

Post by Duncan »

Hi and welcome.

While it is possible for the outer race of bearings to tighten up when they have been inserted in to heated cases with bearing fit I have not come across tight AMC twin ones that have had the securing taps, if it was okay before and you have not changed anything it should still be okay. More often the rollers will fall back slightly in the inner race making fitting difficult, I have read about wrapping cotton around the race to aid assembly but leaving a tail to pull it out once assembled. I normally uses Graphogen to stick the roller in place to stop them dropping back but it can still be fiddly.

If the bearing is good I would advise reusing it as new ones are expensive, to remove the outer race clean back the securing punches in the aluminium around the edge of the race and pop in the oven for about 20 minutes or so, quite often the race will fall out on its own accord failing that bang the cases sharply on a flat wooden surface (be careful to not damage the joint face) and the force should free the race.
theEagle
Posts: 16
Joined: Thu Jul 27, 2017 2:18 pm
Location: CHESHIRE UK

Re: Tight crank bearing

Post by theEagle »

Hi Duncan,
Thanks for the tips, I had not thought of that at all. But since when i split the case I had to drive the sides apart quite forcefully it seem as if the fit might be tight even when assembled? ( = not just the rollers "leaning" out of the cage). But then again, before i split the case I could rotate the crank quite easily, so not extremely tight i guess).
I will still give it a try with the cotton string :) if that is the problem it would be that it would be a huge relief !

If that does not work I should probably try to remove the massive centre-punches and try to get the bearing out just to see if that makes the fit better. But that will be plan two.

Many thanks for the advice. time is always an issue but hopefully I can try soon and we will see.
Cheers
eagle
zwarts
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Joined: Mon Jan 01, 1990 12:00 am
Location: LANCASHIRE UK

Re: Tight crank bearing

Post by zwarts »

Hello Anders. I have come across this problem, some years back, with a Model 30 engine. In my case the problem proved to be a timing side roller bearing with insufficient internal clearance. These bearings are manufactured with a range of internal clearances according to intended use. Where the inner race is a press-fit on the shaft and the outer race is a shrink fit in its housing a C3 clearance bearing is required. It could be that your bearing is correct but after fitting to the shaft, the centre-punching has caused the inner race to expand sufficiently to take up the internal clearance. Centre punching the crankshaft is a barbaric practice and totally unnecessary - 'Loctite Bearing Fit' retaining compound is a far more civilised answer to loose bearings - just be careful to keep it away from the rollers and tracks of the bearing or you will stick the rollers to the tracks and there is no solvent to remove this! I would gently remove the centre punch marks by careful use of emery tape or similar, until the inner race will just push all the way onto its seating. Then, see if the cases will assemble without force. If it still will not go easily together, you will need to get a new bearing with the correct internal clearance.
Once all is well you can then proceed to apply Loctite and assemble when the compound has set.
Good luck, Bob.
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1608
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Location: ESSEX UK

Re: Tight crank bearing

Post by 1608 »

My method would be to remove the centre race with rollers from the shaft and see how it fits with the outer race. If too tight then I would consider a replacement. You can remove the punch marks by CAREFUL use of drilling. If the outer race still will not budge by heating the crank case then I have seen it done by drilling two holes in the crank case and then using a slim punch drive the inner race out whilst the case is still hot. I would check that the bearing is C3 as mentioned above
theEagle
Posts: 16
Joined: Thu Jul 27, 2017 2:18 pm
Location: CHESHIRE UK

Re: Tight crank bearing

Post by theEagle »

Thanks for the input!

Duncan: I tried to wrap in the rollers with a thin thread but it did not work. I think the race is just a bit tight for the bearing. But thanks for giving me some new thoughts.

Bob: Thanks for the reply! But I was probably a bit unclear, it is the outer race that is centre-punched in the case(not the one on the shaft). But those punches are very deep, do you think they can make the outer race to tight for the bearing to fit easily? Thanks for the advice on locktight. How do I see if it is a C3 bearing, is it actually marked with "c3"? (I will have a look)

1608: Ok thanks for the idea with the drill/slim punch to get it out. What is the easiest way to get the bearing of the shaft, a puller? I have seen some youtube vid (from lunmad) where he used some long small angled wedge to drive it off, is this something you have seen before?

Still not sure on how to proceed. Either i just heat the case and try to fit it and hope for the best (is that to ignore a large problem..?). OR i remove the inner bearing or outer race and see how that fits when free.

votes?
In the meantime I try to check if it is C3
Thank you for your input
eagle
theEagle
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Joined: Thu Jul 27, 2017 2:18 pm
Location: CHESHIRE UK

Re: Tight crank bearing

Post by theEagle »

IMG_5038.JPG
Here is the bearing on the shaft. Is the "plate" behind the bearing normal?
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theEagle
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Joined: Thu Jul 27, 2017 2:18 pm
Location: CHESHIRE UK

Re: Tight crank bearing

Post by theEagle »

IMG_5037.JPG
And here is a photo of the outer bearing race in the timing side case halve. There seem to be no indication of "c3" on the bearing.
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1608
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Re: Tight crank bearing

Post by 1608 »

Remove the flat type punch marks just enough ( i'd suggest using a sharp 1/8" wood chisel )and heat the case. If the bearing will not drop out by dumping the case down on a flat piece of wood/work bench then the only way I know of removing it is to drill the case and punch it out. It wont cause any lasting damage. Remove the inner race and rollers with a three legged puller ( leaving the timing pinion in place ) and then see if the two bearing parts are too tight. You should wash the rollers in petrol/parafin and dry them to properly check for wear etc. If not stamped on the reverse with C3 research the SKF number.
ajsph
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Re: Tight crank bearing

Post by ajsph »

You don`t need to drill two holes in the case, first remove the punches,I have turned a piece of alu on my lathe, the diameter must be the same diameter as the outer race, fit it in the bearing and supply some heat and the alu will expand, and a good dash with a soft mallet will do the job
Poul
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