Dominator 88

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Apologies for the lack of feedback but understandably with all that's going on I haven't had a chance to get back into the workshop. Nevertheless, I did have a go at the gearbox this weekend. Stripped it and had a very careful look at everything. The innards are in really good shape and I would be lying if I said I found something really obviously wrong. The only thing I could see was that the spring pushing out the locating pin which locks the camplate seemed really stiff which made rotating the camplate quite difficult - even without the innards. I found no literature on if the spring has a certain length or stiffness or if you need to add shims between the cap and the gearbox to alter the stiffness, so I just put it back the way it came out. The other thing was the timing of the camplate and the selector arm (where the ball fits). Some say you need to time it that in 4th Gear the arm lines up with the top right gearbox stud, and others say that at the extremes, the distance from the notch from 1st and 4th need to be the same. I set it up this way, but I haven't finally reassembled the box, so I can change it if there is a more scientific way to get the timing right!
 
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Still have no clue if you have an AMC or a laydown gearbox. Is the inspection cover round (AMC) or oval (laydown)? Makes it a bit harder to try to help.
According to my notes the camplate plunger spring for the AMC box, part# 040442 is 1.49" long. My notes suggests that a 1.25" long one had been working satisfactory. But here the notes are a bit messy due to some coffee spills.
 
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I believe that your false neutrals and long lever travel is caused by excessive play somewhere between the gearlever and the camplate. Am I correct that the false neutrals appears between all gears? I have a dim memory that there could be a play between the camplate and the gear attached to it. Anyhow worth checking.
Or possibly not correct shimming of the shafts, allowing axial movements. But here I'm not certain if it was the laydown gearbox that could have that problem. A drawback of playing with Burman, Sturmey Archer, Norton, BSA and Velo gearboxes.
 
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That's fantastic. Uplifting, in fact--thanks for sharing.

Is your plan to enclose the primary, or is there some kind of oiling arrangement for the chain?
 
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Glad the link worked! Wasn't sure if it did. It's still very much a work in progress - the previous owner made a chain-guard which I still need to fit, but for now I'll run it open and just use normal Motul Chain Wax. I did notice the oil-tank breather spits oil over the back wheel, so I might actually direct that to the primary chain.
 
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Easily the beast thing you can do is invest in a scottoiler, works brill on the rear chain, would do the same for a primary. The electronic type only need a connection to the battery, fully automatic, adjustable from the handlebars , the only disadvantage is it may be visable . In my opinion chain wax is not a lubricant and is only a little use on a sealed x ring chain.
 
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Glad the link worked! Wasn't sure if it did. It's still very much a work in progress - the previous owner made a chain-guard which I still need to fit, but for now I'll run it open and just use normal Motul Chain Wax. I did notice the oil-tank breather spits oil over the back wheel, so I might actually direct that to the primary chain.
Blow by from pistons?
 
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Well Guys some good news and some not so good news. The oil being pumped out of the Timing cover which I incorrectly assumed to be a high pressure problem was actually due to the timing chest just filling up with oil. Why did it do this? Well, as we were not allowed to ride during our lockdown, I had to be content with just letting the bike idle. I was doing this about a month back and the engine nipped up - I heard it so immediately killed the spark. The next morning however the engine was loose again, so I poured some oil down the LHS plug hole and fired it up - which it did nice and easily. I continued to start the bike on the odd occasion, when about a week ago it nipped up again on idle. Same story - once it had cooled off it fired up ok. I must also mention at this stage that the bike really has no compression - I understand that these engines are only around 7:1 but this still felt really low - you could actually crank over the kickstart by hand. So long story short - our lockdown was extended so I figured I have the time, lets whip off the head and barrel, see why the CR is so low, and also check the piston to bore clearance which I assumed was where the nipping up was taking place.

What I found was not pretty. The previous engine builder had broken an oil ring on assembly, and had just put a new one in, without removing the broken one. You could see the part i fished out of the engine was brand new. Unfortunately, some debris had passed through the oil passages, and blocked up the lubrication hole in the crankshaft for the LHS Cylinder. So with the Oil pump pumping merrily away, and the pressure building, it just filled up the timing cover and pumped out of every small orifice it could find. It took 8bar of compressed air and lots of carb cleaner to finally blow the oil passages in the Crankshaft open.

The only good news out of this situation is that because I was only ever iding the engine, there is almost no damage to the crank journal so I might be able to get away with new shells - but I iwill give it a good measure confirm this. And of course I get to check the low CR - of which I have a question:

The piston to bore clearance is in spec, the rings gaps are still good (I might replace them as a matter of course), and the valves are all sealing nicely. The head has lovely domed combustion chambers, but I have flat topped pistons so the squish area is really big. Given that we can get 95 Octane fuel here in SA easily, would there be any merit in skimming the head slightly to increase the CR? And if so, how much?
 
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You’re a glutton for punishment.

If you’re interested in changing the compression ratio, start by measuring the ratio you have now, by the burette method.
 

Fast Eddie

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How much to skim?

I am a big fan of squish, if you skim to the point where you’ve got a .030”-.040” gap then the squish works and leaves clearance for crank flexing, rod stretching, etc.

But... you’ll have to check valve to piston clearances if skimming a lot off.

And... your CR may still be low with a flat top piston.

As Triton Thrasher has said, if you measure the volume of the combustion chamber, you’ll be able to estimate your approx CR if using a flat top piston.

Whilst you’re down this far, why not go all in...

 
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I've always believed that crankcase high pressure causing oil leaks often is due to piston blowby.
How is your compression?
 
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I've always believed that crankcase high pressure causing oil leaks often is due to piston blowby.
How is your compression?
So interestingly enough, the rings aren't great so I measured the bore to get a reference to order new rings....

Can someone confirm for me - my engine number is 47755 122 which I was led to believe is a 500.....

But the bore I measured now is 68 which means my engine could be a 600. Would it have been possible that down the line someone has converted this engine to a 600? Are the parts even interchangeable?
 
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So interestingly enough, the rings aren't great so I measured the bore to get a reference to order new rings....

Can someone confirm for me - my engine number is 47755 122 which I was led to believe is a 500.....

But the bore I measured now is 68 which means my engine could be a 600. Would it have been possible that down the line someone has converted this engine to a 600? Are the parts even interchangeable?
A 12 engine is a 500cc with short barrels, and is for the original gardengate frame model 7. The 12-2 is the mostly same engine for a 88 featherbed frame. The bore can grow quite a bit but in diameter only, not height. A 12 or 122 engine cases can contain the taller barrels, longer stroke crank, of the 14 600cc engine used in a 99 BIKE.
Only by measurements can YOU determine what your engine is.
Huge overbore 12-2 seem to be common.
 
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Ok so I have been reading a bit.

Correct me if I am wrong:

The Model 7 was a 500 (497) with a 66 x 72.6 Bore and Stroke in a single downtube frame.
The 88 was also a 500 (497) but in a Featherbed frame
The 99 became a 600 by changing the bore to 68 and the stroke to 82?

How did Norton effect the change in stroke - by changing the rod length, or by moving the offset on the 3-piece crank?
 
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A quick check in the spare parts list for 1959 88 and 99.
Crankshaft different stroke, pushrods different length, barrels and pistons different. The rest seems to be the same. Might have missed something.
So to be certain, you have to measure stroke.
It could be that PO found that max overbore .060 was not enough so he had it rebored to 68mm and threw in 99 pistons.
 

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