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That is an awful lot of gearbox slack. Here is my 920 gearbox in second. The gearbox is a $300 eBay 750 Commando gearbox. It is probably stillall original ( not rebuilt) and has had a fair amount of use if the external condition is any indication. I plan to have a good look inside this winter.

Glen
 
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In Australia, there are very few clubs running open road race meetings. We have a Superbike Series, MotoGP and about 3 historic meetings each year. I think most of the young guys only play computer games, these days. Even the hot-rods have been killed-off. I have come to appreciate that when I was young, I lived in a country which was as good as it was ever going to be.
 

storm42

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That is an awful lot of gearbox slack. Here is my 920 gearbox in second. The gearbox is a $300 eBay 750 Commando gearbox. It is probably stillall original ( not rebuilt) and has had a fair amount of use if the external condition is any indication. I plan to have a good look inside this winter.

Glen

A lot yes, but I believe by design. When I first noticed the slack a while back, I had a look inside the box and all was good. I guess it is one of the reason the TTI boxes are so slick in use. Nothing I can do about it and judging by Chris's comments, I am not the only one.
 

storm42

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Ralph have the liners sunk?

I don't think so Nigel, just been and had a look and they sit flush with the barrel, I believe that is how they came. the liners are stepped at the top so they have a positive stop for hight, it is the step that the rear through bolt holes have uncovered.
 

storm42

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In Australia, there are very few clubs running open road race meetings. We have a Superbike Series, MotoGP and about 3 historic meetings each year. I think most of the young guys only play computer games, these days. Even the hot-rods have been killed-off. I have come to appreciate that when I was young, I lived in a country which was as good as it was ever going to be.
yes but, you have this.

 

Fast Eddie

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I don't think so Nigel, just been and had a look and they sit flush with the barrel, I believe that is how they came. the liners are stepped at the top so they have a positive stop for hight, it is the step that the rear through bolt holes have uncovered.
The liners are normally a few thou proud of the surface of the barrel on Steve’s barrels. Discussed recently here:


As I see it, the gasket around the through bolts shouldn’t really have to seal, the gasket should seal by being firmly clamped between the liners and the head.

Are your pistons dished or flat topped Ralph ?
 
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storm42

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They were dished, but are closer to flat now after a close encounter with my mill and a fly cutter.

The liners do sit flush and I believe always have, there is a step in the liner at the top which fits onto a lip in the barrel, unless the top has been skimmed after the liners were fitted i have to assume they are right.

Wouldn't be surprised if it was wrong though. :)

I know the standard barrels don't get so close to the through bolt holes but they seal with no lip so I am no too concerned. also the other side held up.
 
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A lot yes, but I believe by design. When I first noticed the slack a while back, I had a look inside the box and all was good. I guess it is one of the reason the TTI boxes are so slick in use. Nothing I can do about it and judging by Chris's comments, I am not the only one.
I recall your earlier thread about the slack making riding a bit tricky at times. Now I can see why.
I have to wonder where all of this slack develops in the workings of the TTI box. Its not great for the rider can't be great for the box, although the boxes have a reputation for endurance.
I once rode a newish BMW 1200 that had all kinds of driveline slack. The model is known for it and the owner had forewarned me.
The slack combined with a very twitchy throttle made for an interesting riding experience.
I made a real spectacle when attempting to navigate the big thing through a parking lot. Had some spectators chuckling though, so it was worthwhile!

Glen
 
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lcrken

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I like your idea to use alloy plugs over the through bolts. If you continue to have head gasket issues, you might consider fitting a copper o-ring to the cylinder. Back when I first started racing a 920 with sleeved iron barrels, I had similar head gasket problems until I cut a groove in the top of the liner for an o-ring. This is a picture of the area around the through bolt counterbores, showing the o-ring details. The lip on your liners looks a bit narrower than mine, but probably still enough width to cut o-ring grooves.

Counterbore Detail 1200.jpg


Ken
 

Chris

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Hi Al, that would be nice !
Ralph what do you think? Let's chase up all those that were going to come out last year.
Access Norton ride out to Cadwell Park ?
Time to get all of us on the grid at the same time as well?
That would be a grand day out lol
 
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Ralph, any plans for Spa this year? So far, it seems to be on. My friends went last year and reported that they had a really good weekend, so I’m very much hoping to make it this year.
 

SteveA

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So in summary, just another typical race meeting, right? :D

Please keep up the reports. I'm enjoying the read. Brings back a lot of memories. I do envy you just a bit, but hope you enjoy your racing years as much as I did mine. It's been 28 years since my last road race, and 49 years since I was a new racer and going through the (sometimes painful) learning process. Hard to believe it's been that long. When I started racing, my Commando PR was considered a modern superbike!

Ken
Only 46 years since my first race (11th May '75) and nearly 20 months since my last.... ignoring the many seasons away in the middle.... hoping for a return before the end of the year.... still learning....
 

SteveA

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Tyres have changed again since the 60s, this past few years most of the manufacturers seem to be making more focused tyres, the Continentals I use are defiantly better in the dry than the Avons but the Avons are a better all rounder, there are tyres made now that are practically slicks and are a lot faster in the dry, I noticed my times are closer to some of the top guys in the wet but they are using more dry focused tyres, the ones that seem to bugger off no matter what, are changing wheels.

I think the tyres are being moved forwards by the SuperMono guys, the tyre companies have identified a market.

Avons are good, but my experience says Heidenau are better when wet and slippery! Not so good when it's hot, by which I mean South of France hot and dry, not Darley Moor hot! However, your 920 would probably turn them to gum in anything other than the wet!

Other people's experience says that Continental are 'variable', some have reported Contis of a certain vintage being excellent.....and then removing later ones after the first race on them.

The Supermono guys complained like hell when they were told to use treaded tyres, most of them think their bikes can only work on slicks!

They are never going to be as big a market as the range of classics supported by both Avon and Heidenau.
 
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