Twin crank roller bearing tolerance

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LynP
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Twin crank roller bearing tolerance

Post by LynP »

Hi, I have a pair of Hoffman brass caged bearings, which have two circles scribed on the races and I think these indicate they are close tolerance roller to race fit. If I am correct about the tolerance please can anyone tell me if they are suitable for my 1961 G12? Thank you, Lyn (They are the correct size it's just the tolerance I am concerned about)
Groily
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Re: Twin crank roller bearing tolerance

Post by Groily »

Hoffmans that came out of one of mine a long time ago are marked L11 and TH2 on the outer race and LS11 and SH2 on the inner. There is also a symbol like a squashed triangle or delta on the outer. Do yours carry no other identification than the O symbols?
I think the correct fit is a 'C' clearance for these, which is not 'close tolerance'?
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ajscomboman
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Re: Twin crank roller bearing tolerance

Post by ajscomboman »

C3 is the tolerance for these roller bearings if the history is to be believed. Brass caged bearings are unobtainable from the research and enquiries I've made to several specialist suppliers. There was a hiccup a while back when our supplier issued nylon caged bearings, these were promptly swapped for the readily available steel cage bearings that replaced the older brass cage. I suspect that the change came about for cost reasons. Shame as the Hoffman brass ones were superb. Still the club replacements seem to do the job quite nicely and I've had no issues.
LynP
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Re: Twin crank roller bearing tolerance

Post by LynP »

Thank you both for your posts. Groily, the markings on the Hoffman's are RLS 12 1/2 with OG opposite that and the O O for the clearance. Dimensions on the box 1 3/8" x 3" x 11/16". They are new old stock. I also have a new old stock pair of rhp with the the same fitting dimensions marked LRJ1.3/8DESA also MT and then A spaced around the races, I think these are normal clearance, they have steel cages. ajscomboman as you say C3 could well have been the original spec. perhaps fitted to allow a little extra clearance because of the use of the centre plain bearing, are the once the club sell C3 or standard clearance? The problem I have now is which of the bearings I have should I use, or do I need to buy new? I like the idea of the Hoffman's brass cages but if the clearance is to too tight I would not like to chance causing damage having spent a lot on the engine so far. Sorry for such a long post. Thank you again, Lyn
Last edited by LynP on Fri Jun 18, 2021 1:37 pm, edited 1 time in total.
SPRIDDLER
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Re: Twin crank roller bearing tolerance

Post by SPRIDDLER »

Out of stormbound interest I've browsed a bit.
SKF seem to mark bearings with 0 0, 0 1 and and 0 2 to indicate the interference fit/tolerance of the inner dia. of the internal race (i.e. the fit on a shaft) and the outer dia of the outer race (i.e. the fit in a casting). Both can be different from each other on the same bearing.
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Groily
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Re: Twin crank roller bearing tolerance

Post by Groily »

LynP wrote: Fri Jun 18, 2021 12:52 pm ajscomboman as you say C3 could well have been the original spec. perhaps fitted to allow a little extra clearance because of the use of the centre plain bearing, are the once the club sell C3 or standard clearance?
AFAIK most roller mains of these sorts are C3, so I don't think it's a 'centre main' thing. I think it's to do with there being a little bit of flex in all these cranks, which a looser tolerance copes with better (and which a centre main ought on one level to reduce!)
I'm sure many of us remember the problems with some of the Notrun or maybe Trihard twins towards the end of production, and the introduction of 'Superblend' mains. I believe they had slightly barrel-shaped rollers to accommodate a bit of flex - to avoid mullering themselves while not even out of warranty. I'm sure the guy who sold me my P11 said it had them in it, which is comforting.
But I have no idea whether the life of a closer tolerance one would be nasty brutish and short in a Twingle as I've never tested the theory.
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ajscomboman
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Re: Twin crank roller bearing tolerance

Post by ajscomboman »

Groily wrote: Fri Jun 18, 2021 3:28 pm
LynP wrote: Fri Jun 18, 2021 12:52 pm ajscomboman as you say C3 could well have been the original spec. perhaps fitted to allow a little extra clearance because of the use of the centre plain bearing, are the once the club sell C3 or standard clearance?
AFAIK most roller mains of these sorts are C3, so I don't think it's a 'centre main' thing. I think it's to do with there being a little bit of flex in all these cranks, which a looser tolerance copes with better (and which a centre main ought on one level to reduce!)
I'm sure many of us remember the problems with some of the Notrun or maybe Trihard twins towards the end of production, and the introduction of 'Superblend' mains. I believe they had slightly barrel-shaped rollers to accommodate a bit of flex - to avoid mullering themselves while not even out of warranty. I'm sure the guy who sold me my P11 said it had them in it, which is comforting.
But I have no idea whether the life of a closer tolerance one would be nasty brutish and short in a Twingle as I've never tested the theory.
You can get standard and C3 roller bearings but the majority are C3, I've tried looking at the ref number for the bearings we stock and have done so for several yrs without detriment but there is no clear identification if they are standard or C3. Whatever they are, they work and have passed the test of time and use.
LynP
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Re: Twin crank roller bearing tolerance

Post by LynP »

Thank you all for your help and information. I am still not 100 percent sure what clearance the two circles on the Hoffmans indicate. It seems that in the past different manufacturers used different markings. I have emailed a couple bearing suppliers with regard to the Hoffman system and if I get any information I will post it here. At the moment considering that the rhp's have no clearance/tolerance markings they should be usable, what do others think?
g80csp11
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Re: Twin crank roller bearing tolerance

Post by g80csp11 »

2 scribe marks on Hoffman indicate CN clearance ( images in link)

https://www.classicbritishspares.com/bl ... -clearance
LynP
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Re: Twin crank roller bearing tolerance

Post by LynP »

Thank you g80csp11 for the link. It seems Both makes of bearing I have are normal clearance (the rhp's have no clearance markings so CN). My final question is do members think it would be OK to use either of them in my G12, I wondered if others have fitted bearings with normal clearance and what were the results?
I have had the crank, rods and pistons all balanced together so hopefully the vibration will be less! but would this make any difference with regard to be bearings?
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