Rear Main Bearings

[Jeff Taylor]

Quote from David Stepney:
"Having decided to tackle the rumbling rear main bearing on my box saloon that has been getting increasingly noisy since I bought the car in October, I ordered a new bearing from The Seven Workshop. To be fair, Jamie did tell me that he was currently unable to get the RHP bearings and offered me a Hoffman bearing instead. Knowing that Hoffman are a well known brand ordered one, which arrived today. When i unpacked it, although it says it is an MRJ1 1/4" bearing, it is uncaged and, of course, fell into it's component parts as I examined it. The old bearing is a Ransome and Marles caged bearing."

Whilst an original R&M was designated an MRJ1 1/4" an original (pre 1969) Hoffmann would have been labeled as an RMS12 and the equivalent SKF 402318. The bearing dimensions being 1 1/4" x 3 1/8" x 7/8" - this information from a 1950 R&M / Hoffmann / SKF catalogue.

[Chris KC]

Thanks for posting that Zeto, I've been thinking of attempting to make something on similar lines.

[David Stepney]

Thank you everyone for your help and comments. AS promised in my last post, I would let you all know what has transpired;

I rang Hoffmanns and spoke to one of their technical people. He told me that the big difference between a caged and uncaged roller bearing is that the uncaged version will withstand greater loads, including shock loads, but only at a slower speed that a caged bearing. During my net surfing last night trying to find an answer, I came across some bearing data sheets that suggested that the maximum rotational speed fora MRJ 1 1/4" bearing was 12000 rpm for an oiled bearing and 8000 for a greased bearing, the difference presumably because a flow of oil will keep the bearing cooler.

Hoffmans couldn't give me a max rotational speed for the uncaged roller, but given that a standard Seven Box Saloon engine revs to about 3,500 rpm, the uncaged roller should be fine and it appears to be the case that it will withstand greater shock loads that the caged bearing. I have in mind the loads imposed when cylinders are firing twice per engine revolution.

I then spoke to Jamie at Seven Workshop, He told me that RHP stopped making MRJ 1 1/4" bearings about six months ago and he has been struggling to find a suitable replacement. His bearing suppliers recommended the Hoffmann bearing as a suitable substitute. He could get Chinese pattern bearings, but said that he didn't want to go down that route.

So it was Hobson's choice, although I was  a little reassured by the conversation that i had had with Hoffmanns.  So, this morning, after walkmg the dog, I fitted the bearing. I used a cable tie to keep the rollers in position , and, yes, Chris KC, I have used bearing fit on the inner track. I think that reliability and making sure that the inner track has no possibility of spinning on the crank is more important that  than worrying about how to get it to bits in the future, besides, Loctite 641 is destroyed at temperatures above 200C so I do not perceive a problem getting it off if I have to in the future. And I have a puller plate like that of Zetomagneto's ( it is part of a Mini/1100 flywheel puller set that I have had for years) so I can make a serious puller like the one in the photos.

The clutch and flywheel are back on and the only jobs I have to do are to replace two manifold studs and check the tappets. The plan is to get the engine back in and running at the weekend.

The crank certainly turns over more smoothly so I am hoping that the engine will now run more sweetly. Cross Fingers!

[Tony Press]

Jeff,

"Whilst an original R&M was designated an MRJ1 1/4" an original (pre 1969) Hoffmann would have been labeled as an RMS12 and the equivalent SKF 402318. The bearing dimensions being 1 1/4" x 3 1/8" x 7/8" - this information from a 1950 R&M / Hoffmann / SKF catalogue."

R&M Bearing MRJ 1 1/4 and Hoffmann RMS12 equivalent in SKF is CRM 10 - not sure where the SKF 492318 comes from- possibly a later designation for that shown in early SKF listings as CRM 10 AU. I believe this was a variation with special internal clearance and possibly even slightly 'barreled'  'rollers.

I would think the likelihood of finding any SKF CRM 10 AU bearings extremely unlikely so we must use the standard CRM 10.

The recommended shaft tolerance for the 1 1/4" bore bearing is listed  as  k5i: +.0007"  to  +.0003"

---

Ruairidh,

"Would these bearings last longer do you think?
I was discussing with another Forum member a few weeks back how the bearing here needs regular change, unlike the front two that hardly ever wear out. Any help at the back seems a good idea in theory, do extra rollers provide that in practice?"

The full complement Roller Bearing would have greater load capacity which would lead to a longer calculated life.

Having said that as you would understand parallel rollers are subject to roller end loading when subject to miss-alignment - which happens when the shaft 'whips' - I don't know how rigid the Phoenix crank is compared to the standard heavy crank, but still being two bearing I would think some 'bending' could occur.

The full complement roller would tend to be stiffer and maybe more prone to roller end loading ?

[David Stepney]

I think that I am about to find out!

[Tony Press]

Russell,

"I have heard it said that moisture plus periods of inactivity promotes rust and pitting in the rear main. Could a fully sealed bearing minimize this  by virtue of it being coated in grease not used engine oil? Would the bearing run hotter not being flushed in engine oil? In other words are sealed rear mains a good idea?"

The original inch series of Roller Bearings are not available with seals and if they were it would be very difficult to fit.

Also the bearing seals used, while good for keeping grease in would most likely allow the engine oil to get into the bearing and wash out the grease.

[Bob Culver]

Hopefully the clearances acheived are at least in the Normal range. My father reckoned he could detect the difference in new bearings between one, two, three spot ratings.

Much is made of end loading of rollers but in normal use do the roller ends or track edges spall?

Seems relatively simple to sleeve the shaft and turn the housing for a metric bearing. However dificult to find a truly circular housing or to hold it so it stays that way. I can see no probems but will discover.....

The Chinese situation is curious. They produce millions of cars each year and presumably most give service comparable to excellent rivals available in the east. But they seem unable to control poor products. Here imported trailers suffer immediate and dangerous bearing failures. There is so much ultra high precision work in a bearing getting the metallurgy and heat treatment correct would seem a minor effort.
Same applies to many Indian products. A car club imported water pump seals but fail prematurely

[Ruairidh Dunford]

Thank you Tony.

[squeak]

Thanks Tony, that makes sense.

[Chris KC]

David,

It's your call! But I had such a job getting the last one off that the bearing ended up in the scrap bin when there wasn't really anything wrong with it.
Be very, very, careful if you ever have to apply heat to a crankshaft / main bearing. SKF & Koyo (for example) recommend 125C as the max allowable temperature for their roller bearings (beyond which you risk distortions and metallurgical changes).

Are you sure it was Hoffmann's you spoke to? I thought they went out of business decades ago... I believe the name is currently owned by a group which sources / supplies old stocks of their bearings. I had one off them but (as was discussed on this forum) it arrived with (admittedly minor) corrosion etching on the races & I didn't buy another. I think the last new ones were made in about 1990? I'm sure somebody here knows.


Tony,

Do you know a source of SKF CRM 10?
I ran one in my Ulster rep for 30-odd years, though I'll have to dig it out to check whether it was an AU (?) or not.