Crankshaft bearings

[derekn]

Hi everybody, I’m having the engine out of my RP box saloon reconditioned. We have removed the crankshaft and I have purchased the standard 2 bearings for the front and the single bearing for the back of the crankshaft.  We have removed the old single bearing from the back of the crankshaft.  When we tried to fit the new rear bearing on the crankshaft it was loose and could be ‘waggled’ on the end of the crankshaft.  The crankshaft is supposed to be 1.25 inches diameter, so I measured the diameter of the new bearing, and found that it was the correct size to fit a 1.25 crankshaft.  It appears that some time in the past the crankshaft must have been ground to a smaller diameter and an undersized bearing had been fitted to it, even though the outside diameter of the bearing ring was exactly the correct size.  Has anybody come across this situation before? Are undersized crankshaft end bearings available from anywhere, or does anyone have a solution to this? Or am I going to have to buy another crankshaft? Hoping someone can help, many thanks.

[Chris KC]

Derek are you sure the rear bearing is undersize, or has the bearing simply been spinning on the shaft and worn it down?

It's a not uncommon situation. The traditional fix was to dot-punch the shaft all over the mating area and this would raise spots locally to provide some measure of grip. A more modern solution is to build up the shaft by metal spraying, though this generally entails machining off some material to provide enough thickness. Another possibility is to machine a little off and sleeve the shaft. Some just slap it together with some Loctite - depends just how loose it is.

If you choose to follow the latter course, for heaven's sake make sure you are able to remove the bearing from the shaft again! Keeping in mind that you may have to do so with it in the crankcase where it's very hard to apply much force. 

Before doing any such thing or spending more money I would suggest crack testing the shaft and inspecting it carefully for any other defects. You might very well do better just to find another shaft, they are not usually much money.

[Howard Wright]

Hi Derek

I would echo what Chris has said.  These cranks are around 90 years old and most have had a hard life. Failures are not uncommon and may render the whole engine scrap. So crack test and check the journals carefully.

Cheers

Howard

[Robert Leigh]

Many years ago I had the rear journal fairly heavily nickel plated, which is something you can do at home with a relatively cheap kit. It may be that if you follow that course of action you will need to get the plating on the journal ground down slightly to give the tight bearing fit which you should have.

[derekn]

Hi Chris, many thanks for your help.  I think it was an undersize bearing that had been put on.  It was a tight fit when we took it off and when I measured the inside diameter, it was slightly less than 1.25 inches .  I have had the crankshaft crank tested, so it is a good one, apart from the problem with the end of it.  I will have to consider ways of raising the surface or trying to find another crankshaft.  I think it would be better if I could do this and use a standard size bearing, which would help with long term future use.
Derek

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Hi Howard, yes, I’ve had the crankshaft tested, and it was sound.  It’s a pity it has this bearing problem.
Derek

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Hi Robert, your suggestion of nickel plating the crankshaft sounds interesting, this would increase the diameter of the shaft, and then I could have it ground to the correct size to take the 1.25 inch bearing.  I’m having all the chrome parts on the car replated at the moment, and I will talk to the metal plating company about this idea. Many thanks.
Derek

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Derek are you sure the rear bearing is undersize, or has the bearing simply been spinning on the shaft and worn it down?

It's a not uncommon situation. The traditional fix was to dot-punch the shaft all over the mating area and this would raise spots locally to provide some measure of grip. A more modern solution is to build up the shaft by metal spraying, though this generally entails machining off some material to provide enough thickness. Another possibility is to machine a little off and sleeve the shaft. Some just slap it together with some Loctite - depends just how loose it is.

If you choose to follow the latter course, for heaven's sake make sure you are able to remove the bearing from the shaft again! Keeping in mind that you may have to do so with it in the crankcase where it's very hard to apply much force. 

Before doing any such thing or spending more money I would suggest crack testing the shaft and inspecting it carefully for any other defects. You might very well do better just to find another shaft, they are not usually much money.

Hi Chris, many thanks for your help.  I think it was an undersize bearing that had been put on.  It was a tight fit when we took it off and when I measured the inside diameter, it was slightly less than 1.25 inches .  I have had the crankshaft crank tested, so it is a good one, apart from the problem with the end of it.  I will have to consider ways of raising the surface or trying to find another crankshaft.  I think it would be better if I could do this and use a standard size bearing, which would help with long term future use.

Derek

---

Hi Derek

I would echo what Chris has said.  These cranks are around 90 years old and most have had a hard life. Failures are not uncommon and may render the whole engine scrap. So crack test and check the journals carefully.

Cheers

Howard

Hi Howard, yes, I’ve had the crankshaft tested, and it was sound.  It’s a pity it has this bearing problem.

Derek

---

Many years ago I had the rear journal fairly heavily nickel plated, which is something you can do at home with a relatively cheap kit. It may be that if you follow that course of action you will need to get the plating on the journal ground down slightly to give the tight bearing fit which you should have.

Hi Robert, your suggestion of nickel plating the crankshaft sounds interesting, this would increase the diameter of the shaft, and then I could have it ground to the correct size to take the 1.25 inch bearing.  I’m having all the chrome parts on the car replated at the moment, and I will talk to the metal plating company about this idea. Many thanks.

Derek

[Bob Culver]

Random observations, many as above.
 Prudent to crack test. All radii should be generous and not tightened. The original crank tolerance seems to have been +0 to + .00025. Some skill necessary to measure accurately to such limits. Bearings are very slightly u.s, less than .001. Neverthelss the range in tolerances can result in interferece or none on a slightly us shaft.. Loose rear main is common. Processes involving high temp are n.b.g. and lead to failure. Neverthelss common. Any machining must preserve radius. I dont know about nickel but hard chrome plating is very conducive to fatigue. There is not much room for a sleeve. If adept at precision lathe work seems scope to sleeve and to bore housing for a larger (cheaper) standard metric bearing.

[David Stepney]

I had a similar problem with my RP's rear crankshaft bearing, although I know that the old one had spun on the rear journal. My new bearing was no more than a good push fit on the crank, so I used some Loctite bearing fit to secure it.No problems is the 8K or so miles since this was done.

I know that there are some members who don't like Loctite as it can make the rear main difficult to remove again. However, Loctite is destroyed by heating to about 300 degrees centigrade, so warming the bearing inner race with a blow torch should release it.

I used a 'crowded roller' replacement bearing from Seven Workshops (See my thread from April 2019 entitled "Rear Main Bearing") so, when the outer track is removed, all the rollers will fall out enabling the crank with the neer track to be removed and dismantled on the bench.

[Tony Betts]

what markings did the old bearing have on the edges of the outer race.

it may at least have a company stamp, rm rhp etc.

it may even be stamped with a size?

tony.

[derekn]

Random observations, many as above.
 Prudent to crack test. All radii should be generous and not tightened. The original crank tolerance seems to have been +0 to + .00025. Some skill necessary to measure accurately to such limits. Bearings are very slightly u.s, less than .001. Neverthelss the range  in tolerances can result in interferece or none on a slightly us shaft.. Loose rear main is common. Processes involving high temp are n.b.g. and lead to failure. Neverthelss common. Any machining must preserve radius. I dont know about nickel but hard chrome plating is very conducive to fatigue. There is not much room for a sleeve. If adept at precision lathe work seems scope to sleeve and to bore housing for a larger (cheaper) standard metric bearing.

Hi Bob,
Thank you for your wise comments. With yours, and the other responders input, I now have a good number of solutions to follow up. This is my first project of this kind and the amount of instant help and feedback I have received from all is very encouraging.
Many thanks
Derek

[Chris KC]

As Tony's post Derek - if you know what bearing came off I'd have a look and see if it's still available (it was obviously working OK).
It might be that someone has taken it to next metric size (in which case it will be a load cheaper too!) 
Just a thought but have you checked the outer housing is correct size too?

David, heating bearings and crankshafts locally to 300C is not a great idea.