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Dominator timing side main

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Dominator timing side main

Posted by Rob Bradley at December 02. 2016

I'm fettling a 1960 88 for a friend. Most of what I've seen so far has given me a very poor impression of the previous owner's mechanic's skills and I'm wondering how far to go in stripping and rebuilding the bike properly for peace of mind.

It's had new main bearings very recently, but they're both "Superblends" NJ306E-M1. Expert opinion in this forum and elsewhere seems to be that the timing side bearing should be a ball race, M306 C3. I've had a quote of £58.50 + VAT for a Japanese NTN 11-ball bearing.

Four years ago my local supplier said an equivalent was SKF M306NR, so I fitted one to my own Dommie, maybe inadvisedly though so far it seems OK, and I doubt whether it's C3 clearance.

At least one Norton parts specialist sells RHP 6306C3 8-ball bearings for the purpose, and these are widely available cheaply from bearing suppliers, made by FAG, SKF etc. But are these lacking in balls, as it were, and not heavy duty enough, even for a 500 Dommie?

So what's the difference? Is C3 clearance vital? Should I save my friend's money by sticking with two nearly new roller bearings? If the end float needs shimming, are shims available to fit behind the outer race in the crankcase? (From experience, getting the inner race off the crankshaft can be difficult.)

Re: Dominator timing side main

Posted by robert_tuck at December 03. 2016

The 88's std bearings are well up to the job. If the end float is ok I would leave alone. If stripped I would fit a ball bearing which should not be a very tight fit on the shaft. If the case bearing housing is unworn then a c3 will be best.If the bearing is loose in the case then a bearing with less internal clearance will work with locktite bearing fit.

Re: Dominator timing side main

Posted by john_holmes at December 03. 2016

C3 is a later recommendation and allowed a greater interference fit to be used on the cases so the bearings do not spin in the cases,  unless your CN bearings are causing drag on the crank leave them alone. For some reason loctite on a steel bearing outer in an alloy housing does not work for long, my educated guess is the loctite cannot cope with the difference in expansion rates between the metals and gives up after several heating and cooling cycles. A permanent  fix is to copper plate the OD of the bearing or sleeve the housing.

Re: Dominator timing side main

Posted by les_howard at December 03. 2016

Vintage Bearing Company have currently 2 of the 11 ball high capacity bearings in stock. Leave the drive side bearing as it is and swap the timing side for either the standard 6306 ball bearing or the superior 11 ball version. I prefer this set up rather than the use 2x NJ306E's as it keeps to the original design...The price is a TOTAL of £75 (includes VAT and postagel) which is about 9 times the price of the standard type....Frown. Perhaps only fit this expensive bearing if you have everything else downstairs in perfect renewed order...Eg: reground big-ends & brand new camshaft as you should have an engine that should last your lifetime. In std form for a relatively unstressed 500cc engine the std. bearing is sufficient but like most of us we sometimes are not happy unless we take things to their limit quality wise and we can rest happily then.

In addition to what John (above) has said about the bearing outers rotating and (they often do...certainly on the drive side) One fix was to notch out the side of the outer race and fit a screw alongside to prevent the rotation. Also note there are different grades of Loctite...the strongest and hardest one used to be called "Retainer"...not "Bearing Fit" as is often used....check their modern equivalent number...can't remember it of hand....you might wish to use it if your bearing fits too easily.

One other way I though of is to grind a groove across the outer face of the bearing. Then fit the bearing and then with a small HSS drill bit drill along side the groove. As the alloy is softer the drill will drill a neat groove alongside this bearing groove. You can then tap in a small steel peg the same length as the bearing width (or a touch shorter) for a nice tight fit between the two. The alloy case is then peened over to retain the peg.

 

Les

Re: Dominator timing side main

Posted by Rob Bradley at December 03. 2016

Thanks for your considered replies. I'm tempted to check the end float and leave alone if it's OK. On the other hand, the previous owner was a fan of silicone sealant, and probably used it liberally on the crankcase halves. Also, judging from the looseness of the alternator rotor nut and camshaft nut he didn't hold with torque wrenches, and I can't help wondering what he did when refitting the big ends.

A story about rotating timing side bearings. In 1972, shortly after acquiring my own Dommie 88 (which I still have) I rode to visit my girlfriend, now my wife, in Campbeltown Kintyre. On the way down the peninsula the engine seized and I had to be towed about 40 miles by her brother in his car, an experience he still remembers with horror. On stripping the engine by the light of an oil lamp with minimal tools, as well as the pistons and big ends being the worse for wear, the timing side ball race was loose in the case. The only engineer I could find locally was a rough and ready fishing boat mechanic, whose solution was to weld small blobs across the outer race and bash it into place. I hadn't heard of Loctite in those days, maybe it didn't exist. His normal method of sizing little end bushes was to use a file, but I think I declined his offer on that one.

I think I prefer the solutions suggested above!

Re: Dominator timing side main

Posted by les_howard at December 03. 2016

I've checked the Loctite catalog and the best bearing fit product (Equivalent to the old "Retainer" product) is Loctite 620...High Strength and High temp (230 C upper temp)....note Loctite suggests using a primer either 7649 - 7471.

Les

Re: Dominator timing side main

Posted by Rob Bradley at December 04. 2016

With the timing and primary chaincase covers off I can't detect any crank end float at all, so I think it might be wise to investigate further.

Re: Dominator timing side main

Posted by robert_tuck at December 04. 2016

Peace of mind is valuable. If as you say you have found other dubious bodges then thats the way to go.Sounds like the crank is shimmed so a few thou off a shim may be all thats needed . Old rods can go slightly oval and bind if you regrind and fit new shells ,I think this can be avoided if used but servicable parts are refitted .Try not to swop or reverse the rods.Journal radius is worth checking if has been reground before.

Re: Dominator timing side main

Posted by anna jeannette Dixon at January 15. 2017

The Correct Bearing are  Ransome & Marles MJ30.Ball timing side and MJRA30-3  drive side these are still available if you do your research and there not cheap either Norton At Bracebridge street did only fitted the best components available at the time. but having said all this  you can fit FAG NJ306E with made in Germany stamp marked on them  these are a direct copy of Ransome & Marles Bearings   and well up to the job   yours  ANNA J 

Re: Dominator timing side main

Posted by anna jeannette Dixon at January 15. 2017

Hello Now Some FAG bearing are copies and made cheap   so look for the right stamp markings  I have seen FAG super blend  with metal cage, these are the copies  the real ones have a Bass Cage for the rolls   so owners beware of what you're buying  there is some fake Norton parts out there ,   yours  Anna J 

Re: Dominator timing side main

Posted by David Cooper at January 15. 2017

Regarding Anna's post, SKF web site did have a page with pointers on recognising counterfeit bearings. Apparently there's a thriving black market in clean bearing cardboard boxes to be use to present counterfeit bearings. Oddy I seem to remember the counterfeits actually had clearer lettering etched on the sides.

Re: Dominator timing side main

Posted by Rob Bradley at February 14. 2017

Many weeks later, having got the cases apart I can confirm the bearings are FAG India X-Lite NJ306E M1.

Not C3, which is strange, because they came from Norvil who recommends C3 for Dommies in his catalogue.

The reason for the apparent lack of end float is that when fitted, the bearings are tight to go together and get the crankcase halves to meet. This is an issue that was debated on here some years ago by Skip Brolund. In all that debate I don't recall seeing the suggestion that the inner races might stretch when they are fitted to the crankshaft. The inner races are very tight indeed to get on to the crank, and extremely difficult to get off, so I suspect this is the reason, given that when not fitted to the crank they slide easily into the rollers.

So, just as described in that earlier thread, I tapped the crank across with a hide mallet and measured the end float with feeler gauges, and it came to 0.012", which is fine by me.

The crank rotates freely in the bearings when assembled, so as these are brand new bearings fitted by the previous owner, and my friend is somewhat impecunious, I am reluctant to throw them away and start again. If I did, I'd put a 6306 ball on the timing side, which is cheap enough and, I believe, adequate for an elderly 500, but he'd rather not have to shell out for a new NJ306E C3 for the drive side.

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