Thanks to all who helped during my recent re-ringing project. Much appreciated. Wasn't half as bad as I feared, but there certainly were some quirky little challenges (like getting those bloody pushrods to align properly).

Buttoned her up today, took it out for a short run to heat up the motor. Will retorque the head in the AM.

Never entirely discounting the placebo effect, the motor seems to have substantially increased compression - you can hear it in the exhaust note, and feel it in the exhaust gases, which seem to have much more of a "pop/snap" percussive feel to them when you hold your hand behind the peashooter exits.

Some fairly violent popping on the overrun/deceleration, which usually means lean condition. I'll turn up the slow fuel screws and see what happens, but is there any reason increased compression would require a richer mixture? Doesn't seem so, so I wonder if the more likely explanation is an air leak on the intake side - perhaps intake manifold gaskets; mine were a bit dodgy but I had none on hand so....

Thanks again folks. I'll sort out the mixture in due course but right now I can't wipe off my face the big grin from the apparent improvement in compression (and hopefully, oil control). - BrianK

I had exactly the same reaction to my re-ring/new valves - considerably more "pop" to the sound from the mufflers and added pressure on the hand held behind the muffler, also smoother idle at even lower RPM. It will idle nicely down to 500 RPM once warmed up in the garage. However, the compression on the screw-in gauge is around 15 PSI LOWER than it was before I did the work - was 134/138 is now 120/120. Tomorrow will be my first ride on the bike. I suspect the lower compression pressure on the gauge is because it is much harder (slower) to kick through than it was previously.

Thanks Mike. Your top end isn't even run in yet, though, right? Probably increase substantially once it is, I would think?

Can't understand why it would be harder to kick through, other than, again, increased compression? What else could it be?

Ain't it funny, these Commandos have such relatively low CRs, what 8.2(5?):1 or something, and yet when you kick them over you'd swear you were kicking a high-compression motor? Still trying to figure that one out, but since the power band also seems consistent with the (non-existent) high compression, I ain't complainin'.

I tell you, whatever my gauge said now, I wouldn't believe it if it said lower compression than before the work (except maybe by reason of all the carbon I scraped out of the combustion chambers). I'll check it "apples to apples," warm engine WOT after 500 miles or so.

Thanks for your advice along the way (on both this board and BritBike.com), it was quite helpful Mike. Best to you, Brian

Thanks Brian - I also took a lot of carbon out of the combustion chambers/piston tops. So actually I wasn't surprised to see the compression lower. I do expect it will go up once I am able to ride the bike enough to do a bit of break-in. I assembled the pistons/rings nearly dry, just patting a bit of oil from a clean rag onto the side of the piston. I know that dry is becoming the standard nowadays - even told to do so by a friend who builds competition engines currently - but I couldn't bring myself to do it totally dry. After installing the cyl and rotating the pistons through a few times, I then took a clean rag with some lacquer thinner and wiped out the bores. So it was the "semi-dry" or "Almost dry" method.

I'll be riding it for the first time later this AM. Sunday morning before 9 or thereabouts is the only time there is so little traffic here in Mexico City that I can actually get enough room to load the engine.

Good luck to both of us!

Well - here's my progress report. This AM I ran the bike for about 30 minutes up/down the streets here in town near our house. Was able to do some WOT up to 70MPH since there was no traffic at all - I went out a little before 8 AM. Bike ran really well and I was extremely pleased with: the new Brembo master cylinder (several panic stops from 60+ - VERY Impressive); the Fauth fork mod which totally elimanted topping and almost made me want to go LOOK for bumps(!) and the engine. The engine was quite strong - seemed more responsive but, as BrianK noted, I don't want to overreact due to the placebo affect.

Two issues though - one minor the other maybe not. In any gear other than 1, if I wick the throttle to WOT from low rpm the revs come up but relatively slowly to around 3k, then she takes off. If I roll the throttle in progressively it doesn't do that. All carb parts are new; the needle's in the middle position so I need to fool with that a bit. In 1st I don't really notice it.

But I am not to pleased with the compression check. I did a hot check, just after getting back from the ride and got 125 on the left, 135 on the right. That's too much difference. The cold check before this ride (first ride since rebuild) was 120 on both. It had been running quite a bit in the garage over the past few days and it was always 120 on both cyl's until today. I suppose it could be a slight leak from the head gasket - haven't re-torqued but will later today. I guess it could also be inconsistency in the kicking but I did it twice on each cyl and got essentially the same both times.

But the bike felt great - both quite strong and very smooth! It is idling beautifully at around 700 RPM.

Here's a pic taken just after I got back from the ride. Didn't realize my hair was THAT gray. Yeah, I know, I need to change those jacket patches.

which usually means lean condition
--------------
Or air leaks at the exhaust flanges,
Dave.

raising the needle clip one ought to fix your bog.

And at least you HAVE hair....

BrianK wrote:
Ain't it funny, these Commandos have such relatively low CRs, what 8.2(5?):1 or something, and yet when you kick them over you'd swear you were kicking a high-compression motor? Still trying to figure that one out, but since the power band also seems consistent with the (non-existent) high compression, I ain't complainin'.

Probably due to the long stroke and undersquare cylinder dimensions. Modern motors run higher c.r.s and burn cheap gas with no pinging, but their bores are much larger than their strokes. (They also have more eficient combustion chambers, hemis are old hat)

daveparry wrote:which usually means lean condition
--------------
Or air leaks at the exhaust flanges,
Dave.

That's a thought. I did buy new Suzuki exhaust gaskets but didn't use them (had trouble getting the exhaust nuts to go on straight with them). I'll put them in and see if it makes a difference. Thanks - Brian

EDIT: New gaskets and retorquing made no difference.

Anybody know of anyone who's making higher quality intake gaskets - RealGaskets.com doesn't but perhaps someone does? Guess I could get some material and cut my own, but as you guys may have noticed, I'm something of a klutz....

Found my problem - intake leak on the right carb - gasket defunct; new ones ordered.

You guys probably already know this but for locating an intake leak, spraying the suspect area with WD-40 works a treat. My idle ramped up considerably each time I hit the problem area with a spritz of the stuff. Could na' been easier.

MexicoMike wrote:I had exactly the same reaction to my re-ring/new valves - considerably more "pop" to the sound from the mufflers and added pressure on the hand held behind the muffler, also smoother idle at even lower RPM. It will idle nicely down to 500 RPM once warmed up in the garage. However, the compression on the screw-in gauge is around 15 PSI LOWER than it was before I did the work - was 134/138 is now 120/120. Tomorrow will be my first ride on the bike. I suspect the lower compression pressure on the gauge is because it is much harder (slower) to kick through than it was previously.

Mike
As you can see my gaiters don't extend all the way up like yours do. Where did you get those. I just added them when I rebuilt the forks; I just had the boots on before but I like gaiters. The top diameter was too large and I had to use the old fork seals and add hose clamps over the seals at the top. Yours are obviously the correct gaiters and fit properly; I want a pair like those.
Also I have a question. My top pipe, the right cylinder, has a nice pop to it when I hold my hand over it, but the left doesn't. In fact it sometimes seems as if it is sucking as well as pumping which I guess is normal on the decompression, but I don't get that on the right. I have checked the compression and got from 140-160 left and 150-170 right with a push in gauge. My wife was holding it on the lower numbers and I think she couldn't hold it in with enough force. When I got the higher numbers I was holding the gauge and kicking it, but I didn't realize I was supposed to hold the throttle open. So not being able to do three things at once I enlisted her aid and got the lower numbers with the throttle open. I actually expected higher pressure with the throttle open. Also my plugs seem to get real sooted up except right at the electrode.
Any thoughts?
Bruce in Chihauhua

Try that left cylinder again, warm engine, WOT. Then pour a tablespoon of oil in through the spark plug hole and repeat.

I got a substantially higher reading doing this, which told me my rings needed replacing. Did that and found joy!

Good luck.

Rings wore out on left first for me too, smoked badly on acceleration I was told, new rings and it was sorted.

69750S wrote:As you can see my gaiters don't extend all the way up like yours do. Where did you get those. I just added them when I rebuilt the forks; I just had the boots on before but I like gaiters. The top diameter was too large and I had to use the old fork seals and add hose clamps over the seals at the top. Yours are obviously the correct gaiters and fit properly; I want a pair like those.

They should be available from your usual Norton Commando parts supplier?

http://www.nortonmotors.de/ANIL/Norton% ... 021&Part=6

My gaiters are from "Old Britts" - as I recall they are the oem style gaiters for the 1970 Commando. Re the weaker side exhaust...are you talking about at idle? That could simply be the carb settings. Mine will do that (weaken/"suck") just by slightly adjusting the mixture on either carb 1/8 turn out of the optimum position.