Tappet Clearances

Out of curiosity, I decided to compare Cold Tappet Clearances recommended in various contemporary publications. I was surprised by the variation.

Garrett's Norton Manual for all twins 1949-1960: Inlet 0.002", Exhaust 0.003"
Norton's Owner's Handbook for the Model 7 & 88: Inlet 0.002", Exhaust 0.005"
Frank's Norton Manual for the Dominator: Inlet 0.002", Exhaust 0.005" Haynes Norton Twins Model 7, 77, 88 & 99: Inlet 0.005", Exhaust 0.005"
Clymer's Norton Manual for Heavyweight twins: Inlet 0.006", Exhaust 0.008"

What is the current consensus?

From Norton Twin Cylinder Manual (Norton Publication - no date)

Jubilee & Navigator : Inlet - 0.004", Outlet 0.006"
Electra & Heavy Weight Twins: Inlet 0.006", Outlet 0.008"


From Norton Owners Manual (Norton Publication - no date)

Model 88 & 99: Inlet 0.003", Outlet 0.005"
Model 650, Atlas, Scrambler: Inlet 0.006", Outlet 0.008"

Comparing your info and mine, there are differences. With regard to tappet clearances, always best to err on the wide side.

Question? Do any of the clearances change using aftermarket third party pushrods?

Slick

Different camshaft lobe opening ramp profiles require different cold tappet clearances. I normally just use whatever the factory service manual says.

For example, factory specs are as follows:

Stock Commando cam .006" intake and .008" exhaust.
2S cam .010"/.010".
3S and 4S cams .016"/.016".

Earlier twins (pre-1961, or thereabouts) had different cam profile than Commando.

Standard models 88 and 99 are .003"/.005".
SS models 88 and 99 require .006"/.008" (same cam profile as stock Commando)
Model 7 Dominator is .002"/.005"

Ken

texasSlick said:

Question? Do any of the clearances change using aftermarket third party pushrods?

Slick

Click to expand...

As long as they are still aluminum alloy, I don't see why there would be any change. Almost all the aftermarket alloy pushrods use the same 2024-T3 material, or something very similar, so expansion rates should be the same. If switching to steel or titanium material, the clearances are very different. With steel pushrods, you've got to run much tighter cold clearances, sometimes as close tozero as you can get and still start the bike.

PS - Didn't mean to duplicate your post, Slick. Didn't see it before I clicked.

Ken