Motoscrubs.com

Hi George, been there done that! Sorted those the first time around. I will have to give everything a detailed clean and see where the wear is; whatever it is will mean £££££s!

Duccout wrote: It is funny how much improved the bike is, it almost feels like a new bike.

Eagle eyed readers may remember me referencing top-end engine noise a few posts back? Today I thought I would check things over to make sure all was well. I adjusted the valve clearances and shone a torch onto the cam lobes and all was good, so just about to refit the valve covers, I was turning the engine via the back wheel and observing the top bevels, when I heard a strange sound from them. Looking closer, it soon became apparent that as the cam lobes load the valve train, the top bearing bush was moving sideways in its housing. Doom and gloom.

I'm surprised that this is happening, because the bush was not loose, but I suppose that the housing has worn oval under the sideways pressure of overcoming the weight of the valve springs. So, now I need an oversize bush, but what size? And while the head is in the engineering shop, I'd better get one of Nigel's exhaust port repair inserts fitted. Bummer.

All apart. Top bevel bearing tight in sleeve, but sleeve loose in head! After much gnashing of teeth and pondering, I've ordered a 1st oversize sleeve, so we'll see how that looks. I've also ordered an exhaust thread repair insert, although whether I can find anyone who will fit it is another matter. I asked my usual machinist a while ago and he was not keen.

I'm thinking of modifying the bevel tunnel to try to keep the top sleeve in place, along the following lines: the top bevel sleeve sits just proud of the gasket surface (about 3 thou) when it is pressed into the head, and the bearing just inside the bottom lip of the sleeve. My plan is to machine off the lip that is at the top of the bevel tunnel, so that the top flange is flat, place shims on top of the bearing so that it is level with the bottom of the sleeve, then assemble the bevel tunnel using silicone to seal the flange, hopefully physically holding the sleeve and bearing tight in the head. Any thoughts?

Hi Colin

assemble the beveltunnel without the gasket . measure the gap between tunnel and cylinderhead and cut a gasket
from paper in the thickness you measured then the bearing sleeve will be a tight fit .

the top bevel bearing housing get loose in the cylinderhead because the housing keeps turning around in the head
when it is not a tight fit . the very last Mototrans engines had a small roll pin in the flange and a small cutout in the bearing housing to prevent from turning .

a simple solution would be a very small blob of weld on the outside of the bearing housing and line that up with
one of the 2 oil channels in the head . this way the housing cant turn anymore .

Cheers Eldert

Thanks Eldert, but my engine is a Mototrans, with the roll pin! It seems that the bearing sleeve has been chattering up and down in the head, and if I measure the worn areas and compare the size to the unworn areas where the oil drain channels are, the sleeve has worn about three thousands of an inch. I suppose that the original gasket was too thick, which allowed the sleeve to move up and down.

You may recall that I had similar problem with my top bevel housing. I am having a new housing made that will be light push fit in head so that I can remove easy for adjusting bevel gears. The bottom lip will be a few thou. proud of tube recess. This should give positive grip on housing. When set up I will add smear of silicone seal and not have a gasket. Although having housing made is more expensive than an off the shelf one I am hoping to improve what I think is a poor design for Mototrans models.
I have left head and tube plus old bearing housing with a small engineering company so that he can measure accurately. The man that owns the company is a fellow Essex VMCC member and he is reliable.
I hope to finish head and complete engine next week.

Hi George,

The top bevel housing on the Singles seems to be a common problem, possibly because the original engine was only a 125, but then grew bigger, and bigger. Funnily enough the big vee twins use basically the same design, only beefed up, and I have never known a problem with them, although I'm sure that it happens. Although my sleeve had the roll pin to stop it spinning, that did not stop it from fretting up and down, and looking at the gears in-situ, it is apparent that there is substantial sideways forces to deal with as well as up and down. I (as a lay - man) would have thought that the lip at the bottom of the sleeve should have been much wider, to give a bigger clamping surface, to lock the sleeve in place.

I may need the phone number of your engineer!

Colin

Colin should have mentioned that I am having a wider bottom lip made for the reason you mentioned. I will let you know how it all turns out. Chap is ex tool maker and also works on marine engine's

Aye Colin,

Might I suggest that you speak with Andy or Stu at SCR Classic Motorcycles, they know their stuff and are over the county border from you in Cambridgeshire, not that far away. Both race Ducati 250' against each other, although the business has curtailed this in recent years. The link to their website is below and gives only a small insight into their capabilities.

Link: SCR_Classic_Motorcycles

I hope you get it sorted.

Good health, Bill