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Small end bushes

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My Dominator 99 requires new small end bushes - too much wear and it rattles like an old tin can.

I would like to not have to remove the engine and then split it.

Can the bushes be pushed into the rods and then reamed with the engine in place?

Any ideas?

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Yes they can, but you need to set up some type of support to ensure the reamer goes on at 90 degrees to the rod.

yyy
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hello in engineering there is only one way the right way  And the right way is to remove the engine and split the cases and remove the crank shaft and then remove the conecting rods so then the can be millled under a engineers mill drill  and the bronze bushing can be heated and changed for new ones and then reamed to size  and then the large end shells can be changed as well after inspecation now by doing things the lasy way  you willonly end up with metal particals falling into the crankceses  and getting into the oil feed and doing damage in time to come so do thing the right way from the off , yours  anna j   

yyy
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.. the Anna that recommended using grinding paste in bushes? The right way?

I've never had a problem with reaming little ends in situ provided care is taken not to drop any shavings in the crankcase. Actually the odd tiny bit of phosphor bronze is unlikely to cause a problem anyway as the amount a reamer takes off is minimal.

yyy

All the older books about British bikes mention the home made bits of tube with washers and nuts to fit remove and refit bushes. They casually say to ream to get a good fit on the small end pin. No mention of heat!

I have fitted them in situ this way but it is very hard to avoid a slight taper because of reamer wobble because you can't support the reamer or rod! If I did them this way, I would check the bush on the pin prior to fitting and if necessary,  bore it out a bit so when it was fitted, the reamer was removing a minimum amount. Loads of rag stuffed into the cases. Bronze swarf may not be as harmful as steel but if sucked through the coarse mesh of the crankcase filter to the return side of the pump, it is unlikely to improve pump performance!

My preferred method was to remove the rods, again check the ID of the bush prior to fitting and as I was fortunate in having access to a Delapena hone  home the bush to size. This gives a really nice parallel fit.

yyy
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Thank you Anna for your advice, and of course you are technically correct.

However, I must consider the work and risk involved in doing it the correct way against doing it the "easy" way. The bike being 1961 (= nearly 60 years old) is not going to be doing long distances, only to nearby shows, occasional ride-outs, maybe 500 - 800 km a year. As it has been rebuilt (someone else did the engine, I bought it with bills and papers showing the work done on the engine, so I didn't strip it. Foolish!) taking it apart again will almost certainly create some scratches, leaks etc.

Dropping shavings in the case can be avoided by using strong plastic sheets and good sticking tape.

What worries me more is getting the final reamed bore exactly true so that the pistons are not at a slight angle in the bore. Even a small deviation could result in the piston having noticeably more clearance on one side than the other.

I will not attempt the work myself, a reputable engineering shop nearby said they will look into it. So I must get the bike there on a trailer, they will push the old bushes out, fit new ones and ream them without splitting the engine.

That's why I thought I would ask advice.

As it stands, I will go the "easy" way - if they agree to do it.

I'll let you know what happens.

Thanks again.

 

yyy
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you rarely need to take more than a smidgeon off with the reamer. If you use the expanding type it's fairly unlikely you'd get any significant misalignment - or maybe I'm just not as picky as some!

As you say, for the low mileages most people use their Nortons for, absolute spot-on accuracy isn't really necessary. And when you strip engines and see the state they've been running in quite happily for years it makes me at any rate less bothered about total precision. But others of course have different standards.

yyy

Hi Richard,

You didn’t say how long the little end had been rattling, if it had been for some time the fatigue life of the con rod could be reduced but there is no way of accurately telling, hopefully it has developed since you got it and therefore you will know.

If you can buy a reamer with the shank the same size as the cutting end and is long enough you can remove both pistons and use the good little end to guide the reamer through the new one. I would replace both little ends anyway as they will have both done the same work.

As already stated plenty of rags in the crankcase top, covered in duct tape then before removal blow clean with the compressor but watch where you blow the swarf.

Happy Reaming

Dick

yyy
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Luckily I've not found a reason to do this. But won't an adjustable reamer that's long enough to go through both ends make sure the pistons are parallel? What are the tolerances? When hot, the little end in its alloy rod must grow a couple of thou relative to the steel gudgeon pin.

yyy
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Probably not much in it, as the pin will be hotter than the rod.  Hopefully the pin will be newish   as .it has been rebuilt. I have found wear on pins .

yyy
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When I was an impoverished student in 1977, I was decoking my Bonneville and found one of the small end bushes was shot by the fact that I could rotate the piston in the bore by several degrees! I took the barrel off and Reg Dearden the Norton dealer; who was just around the corner, agreed to fit and ream the bush in situ but would give no warranty on the job. They did an excellent job for very little money and the bike was fine after that. Just as well as my skill, available tools, cash and confidence level was no match for a full engine rebuild.

It may not be ideal but it can be done well by skilled artisans.

Hope it goes well.

yyy
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 .... for your advice, it's been most helpful.

It has convinced me that it is not necessary to split the engine. Yes, I may get a better result but it is obvious from what you have said that the easy way is ok.

Given that I live 65 km from the engineering shop, and would have to do a 130 km round trip with a trailer, I'll try to get a reamer and do the job myself. Maybe.

Richard, since its rebuild, it has done only a small mileage. I bought it about 10 years ago as a complete package, repainted, etc, etc, so all I had to do was assemble it - HAHA! As I am sure some of you could have told me, it didn't work out that way. Wrong rear mudguard, shock absorbers and so on. The final insult was when I stripped it recently to fix this rattle, I found it has 500 cc pistons in it, (of course also 500 crank, barrel and pushrods) in a 600 crankcase. The general condition of the engine is good and I am now trying to find the correct parts to get it back to a 600.

In the meantime I acquired a 6 cylinder Honda CBX which had been lying in the back of a garage for 10 years and was asking to be rebuilt. So I obliged and work on the 88/99 came to a halt.

Now, 5 years later, neither of them are really completed (I also took on a ES2 which requires some more work to finish off). Oh.. and I must not forget the 900 SS Ducati! 

Do I hear 'masochist' from anybody?

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yyy

In reply to by ian_soady

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hello Ian  I have Never recommended griding pastes  for camshaft bronzes bushings  read your theads properlly  I told you all about timesaver Bronze lapping in paste  witch is made of lappng in bronze bushings   Time saver cost 33 ponuds a jar  and comes in fine power form  and is mixed with light grease  and you only need a small mix   and with reaming you need a gider to keep thing at the right angels  so you do not have a run out of line  yours  anna j

yyy
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hello  well there is a easy way  warm up the old littel end bushies a push them out and then reame the new bushes before  fitting this way you get a good fit by trying them against the pins and warm them up  in the same way as you removed them  and fit job done  but if the small ends are onthere way out  the large end are not far behind  so splitting the cases mybe a better idea  and check every thing  you may find the rattles somewhere else like the camshaft bushings         yours anna j 

yyy yyy
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Surely by the time the barrel is off, it is little more effort to remove the cases and split them. If the small end is shot, then suspect the bottom end as well, so might as well do all the  inspection / jobs while the opportunity is available. 

yyy yyy
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CBX equals 3 X the bushing problem than that of  the 99!

yyy

Hi David, 

Regarding tolerances and differential expansion, the coefficient of linear expansion of steel is 0.000012 and that of aluminium 0.0000023 (almost twice). (ignoring the bronze bush)

The Gudgeon pin is approximately 0.69" dia. so if we assume that there is zero clearance at 0 Deg. Celsius and the temperature of the engine is raised to 200 Deg. C. then the pin diameter would  increase by:-

0.69 x 200 x 0.000012 = 0.001656"

and the con rod bore would increase by:-

0.69 x 200 x 0.000023 = 0.003174"

giving a clearance of 0.001518"

If my engine got to 200 Deg. C. I would be worrying about other things more.

Cheers

Dick

yyy

Hi Dick,

I would be worried if parts of your engine never got above 200 Deg. C.. 

Admire your calculations and they are very illustrative of differential expansion. I believe that the charge of combusted air in the combustion chamber can be 400 to 450 Deg. C. Less if the combustion is weak, rich, or petrol in fine droplets. It also depends on compression ratio.

The piston top surface doesn't melt because the heat is conducted away through the piston material to the cooler cylinder walls and piston pin and con rods. These in turn are kept cool by finning and oil spray.

Pistons can melt if there is pre-ignition and the charge is fully burned in the compression stroke. The hot charge, the compression, and the longer exposure to very high temperature in the combustion cycle locally melts the piston upper surface.

An engine is fairly complex and there will be others who will be able to add to my fairly simple view of a device to extract the most mechanical energy out of an intermittent explosion.

Regards

Peter

yyy

Hi Peter,

I agree with all you say, I made the mistake of saying 'engine' when I should have said gudgeon pin.

I used the arbitrary figure of 200 deg C to keep it below the 230 deg C 'flash point' and 260 deg C

'flame point' of engine oil'.

Pleased you liked the illustration.

Regards

Dick

yyy

 

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