Valve clearance question

It looks like nobody knows... It's not the alloy pushrods. 88s & 99s with alloy heads & pushrods are .003 & .005 unless they are SS variants. I am guessing then it's either to do with the cam profile or to allow a little extra clearance as the SS models were expected to be thrashed harder and hence get rather hotter at the top end.

The SS camshaft is marked (and this is off the top of my head so likely to be wrong) X1 or X2 but of course you would need to strip the bike to take a look.

In all honesty I don't think it would hurt to leave your clearances at .006 & .008. Better that than tight. I set the valve clearances on my Atlas the other day and it's just as noisy as ever.

Hello To All The High lift Camshaft Thats Know As SS , Was First used in the Norton Manxman 650 some the Parts from the 650 where used to built the engines of the 88ss &99ss Like The Camshaft profile and cam followers &pushrods and Crankcases and later the Cylinder head , So if your up rating Your 88 then you will need the flat Cam followers too and the Fat type push rods as well as the Manxman camshaft number 22729 . hope this helps yours AJD

Previously wrote:

I'll keep wearing the earplugs then...I have flat cam followers and fat push rods, but I suspect the previous owner put a standard 88 canshaft in. That would match the fact that it came with only a single 25mm cconcentric carb (it now has twin 28mm concentrics). He told me he was more interested in flexibility than speed (he lived in north London at the time).

Hello David Sorry to hear you have too where ear plugs , but if you fit the camshaft that the number 22729, I have put on this thread you will not need to wear ear plugs any more ! your ajd

Don't forget the old adage 'a slappy tappet is a happy tappet'.

Ear plugs - the greatest tuning and performance aid ever invented!

Interesting thread Mr. Cooper. If you have .300 lift that does sound like the very early cam from the early 50s. After that they put a bigger cam in, the Daytona cam, and next they altered the Daytona cam and stamped it "QR", which allegedly stood for "quietening ramps". After that the SS came came out next for the 650 Manxman and SS and it was stamped X1.

It would be easy enough for you to try the lash setting for the old cam on your bike instead of the lash specs for the SS cam. Since Norton used steel pushrods on bikes with both iron and alloy heads through 1956 on two different cam profiles it may not have been a reason for any lash change later on. They changed to more clearance with the more modern QR and SS profiles, so that may be why your engine is noisy.

May I ask what year your 88ss is?

BUT, I just thought, that since you may be running flat tappets on a cam profile designed for radius tappets, all bets are off as to what might be going on in your engine. Such a parts cocktail may be beating itself up and filing your engine with filings..... Maybe next winter it will be a good time to get matching parts in there that are designed to go together.

BUT, I just thought, that since you may be running flat tappets on a cam profile designed for radius tappets, all bets are off as to what might be going on in your engine. Such a parts cocktail may be beating itself up and filing your engine with filings..... Maybe next winter it will be a good time to get matching parts in there that are designed to go together.

The best way to check what you have is to check the cam timing which is different with the SS cam. Smaller clearances will change the timing from what the designers intended. You will need a degree disc and a couple of hours. Standard bikes were often hopped up to SS spec but genuine SS bikes were rare.What year is your bike and does the motor have proper SS stamping?.

David

I've got an SS which was converted to single carb too, seems like it was a more popular choice than you would think. My cam is stamped X1, but it has a bad D/S journal, so I bought a new cam from Newman cams for £75 +VAT (I couldn't find anyone who would metal spray/hard chrome/hard face and regrind the old one for sensible money). The profile of the new cam measures just about the same as the original and agrees with Dave Comeau's data. The receipt says it's for a Dominator SS, but the label on it said Atlas. I don't have the equipment to compare the ramps properly though.

The recommendation used to be that stoning the old followers to run-in with properly with a new cam was enough - any thoughts on that anyone?

Even if the barrel, head and pushrods were all fabricated from the same alloy they would all heat up and cool at differential (and to some extent unpredictable) rates. The minimum clearance you could use with a traditional cam would thus be the maximum differential expansion occurring in practice, so that in the worst case situation the valve would seat with zero tappet clearance on its base circle. That would ensure that the inlet valve would seal, and that the exhaust valve would cool and seal, for most of the 720 degrees. To that clearance has to be added the quietening ramps, which I think came in from the late-50s on british bikes. Most likely the size of the quietening ramp would be the dominant factor over the thermal expansion factor - otherwise why would different cams designed for the same engine and valve train require such radically differing clearances?

Obviously an engine with higher output tends to have more heat to dissipate (the exception being power gains resulting from engines having a high compression ratio, which are more efficient thermodynamically, and thus should run cooler, all other factors being equal). Assuming that the first factor was entirely due to differential expansion between different materials, that expansion would be proportional to the temperature rise, and assuming that heat transfer coefficient of the fins was the same (mostly relating to road speed - proportional to the square? dredging now...) then the heat to be dissipated would be proportional to the engine's output in hp - and thus the engine's temperature differential from ambient would be proportional to the engine hp - not that much difference, maybe 10% - 20%. Of course you would only need to ride 5% to 10% faster to compensate.... In a comparable case, you probably wouldn't go for more piston clearance for ordinary road use for an 88SS over an 88.

So I reckon you should use the tappet clearance recommended for the standard cam you've got, and ignore the different valve train. Add a couple of thou for luck.

Dave Comeau's data show pretty clearly that the ramps on a standard 88 are much smaller than the SS cam.

Head going below parapet .......Now!

Steve