G80 Main Bearings & Spacers

LoneStar · Post by **LoneStar** » Sat Apr 07, 2007 12:42 am

Folks,

I've taken on a project bike, a 1954 G80S, said to have been 90% restored. This figure was exaggerated, since the crankcase and most bottom end components are unusable. I'll be assembling an engine from spares, including the crankcase halves, big end, crank axles and timing side bush. All but the cases are new. However the engine came with a pair of drive-side main bearings that appear to be new, so I'd like to use them. This has plunged me into the murky waters of bearing brands and spacer selection.

Here's what I know:

There are two bearings in the case recess, normally identical, with two washers/spacers between them.

The '54 spares book tells me "The standard make of ball bearing used on the driving side flywheel axle is 'SKEFKO'. Those bearings are in short supply, and it has been necessary to use ball bearings of American 'HOFFMANN' make. Spacing washer 010628 is used with 'SKEFKO' bearings, and spacing washer 014830 is used with 'HOFFMANN' bearings."

In addition to one of these, 017194 spacer is used.

My new bearings are SKF RLS8-2RS1, made in Spain. I also have a spare SKEFKO RLS8, made in England and a spare HOFFMANN LS10 made in USA. The latter two are unusable, but handy for comparison. All three are .625" wide, but the thickness of races varies. (picture: http://www.vincent-hrd.co.uk/images/bearings.jpg)

Here's what I'm not clear on:

Given that all bearings are the same width, why use different spacers with different brands?

What's the point of the spacers? If only to separate the bearings, why two, and of different diameters? (017194 is 1 5/16" x .055, the other I have is 1 13/16" x .066) Maybe an oil management issue?

Do I have the SKEFKO or HOFFMANN spacer?

What are the differences between the two?

Which spacer is needed for the SKF bearings I plan to use?

What terrible disaster befalls an engine with an incorrect spacer?

Sorry for the lengthy post, but any wisdom will be appreciated.

Cheers,

Dave Hartner

lolski · Post by **lolski** » Sat Apr 07, 2007 10:05 am

hi lone star may not be of much help but a bearing supplier once told me that skefko is the old name for skf bearings whiched changed its name about ww2 i had my 350 gls bottom end rebuilt and the man said that the two main bearing do have different tolerance but i sure some body will be of more use of info for you
regards

Laurence

LoneStar · Post by **LoneStar** » Wed Apr 11, 2007 7:22 am

Laurence,

Thanks for the info. I did a bit of research, and it's true that SKF was formerly SKEFKO; apparently they changed the name in the 1970s. So perhaps I should go with the SKEFKO spacers, although it's a bit unclear if the relevant factors on those bearings have remained the same over 53 years.

Dave

Don Madden · Post by **Don Madden** » Wed Apr 11, 2007 11:04 pm

Hi, Dave. The purpose of the original, pre-1955 set-up was that the narrow spacer kept the 2 bearings apart preventing interference. The wide spacer acts as as a baffle to prevent excess venting into the primary case.

Later, they replaced the inner main with one of smaller OD & the stepped bore required eliminated the need for the narrow spacer. On these, the outer bearing is a tight fit in the case & the inner is a slight interference. The inner is shifted to set end play of the crankshaft.

I don't think it makes any difference which wide spacer is used as long as the bearing is covered between the inner & outer races to permit the baffling.

You may contact me direct if you with a PM if you wish, or share the info on this forum to benefit more members.

Cheers, Don Madden on the Left Coast.

Peter Lecompte · Post by **Peter Lecompte** » Thu May 10, 2012 12:09 am

Hi Don,

just reading your comment regards main bearing spacers. I have an 1949 18 engine that was recently rebuilt using bearings with shields. The engine builder said he removed the inner shields to allow lubrication to the bearings. He did not fit any spacers between the bearings but fitted a spacer on the inside of the inner bearing to get the correct end float. Is this a sound practice or am i likely to have some problems? I have not run the engine yet, but it is in the frame and almost ready to start. Thanks Peter

wilko · Post by **wilko** » Thu May 10, 2012 2:04 am

I too have wondered why different spacers for different makes? One would think the bearing dimensions would have to be the same no matter who made them!

itma · Post by **itma** » Thu May 10, 2012 3:57 pm

your engine rebuilder knoweth not wot he doth done.
they are there for a reason.

these people who think they know better than the makers are the curse of vintage machines.