Timing Covers 1968 Atlas, 1968/9 Commando, 1971 Commando

APRRSV

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Can anyone tell me if the later Atlas/G/N15 timing covers are suitable direct replacements for early Commando timing cover (points behind cylinder) part # 06-0716?
Also, are the later Atlas/G/N15 timing covers incompatible with later points at end of cam Commando crankcases?
My question relates to oil hole positions etc.
I realize that the later, 1970+ bikes had points at end of camshaft and timing covers were different.

Thank you,
Ed
 
Last edited:
APRRSV said:
Can anyone tell me if the later Atlas/G/N15 timing covers are suitable direct replacements for early Commando timing cover (points behind cylinder) part # 06-0716?...

...My question relates to oil hole positions etc.
Click to expand...

As far as I'm aware, only Commando timing covers (pre-850 Mk3) and therefore crankcases had the return drilling from the OPRV.

APRRSV said:
Also, are the later Atlas/G/N15 timing covers incompatible with later points at end of cam Commando crankcases?...

...I realize that the later, 1970+ bikes had points at end of camshaft and timing covers were different.
Click to expand...

The (20M3S) camshaft points engine was introduced from eng. 131257 at the beginning of 'S' Type production in March 1969, however, both the Fastback and 'R' type continued with the (20M3 points housing behind the cylinders) engine until later that year when the Fastback changed to 20M3S from 133688* (there is no known record of the 'R' type engine changing to 20M3S).

*( A couple of reports of Fastbacks with the 20M3S engine prior to 133688).
 
The points behind cylinder timing cover was unique to Commandos, as was the timing side crankcase. The pressure relief valve on the Atlas/G15 type vents back into the timing chest, where as the Commando type vents back to the return line. You can use the Atlas type cover on Commando cases if you fit a blanking screw into the return drilling to seal it off.
From looking at my notes for my '68 Commando the cover should have AB1 25186 cast into it.

Martyn.
 
If anyone in the U.K. has a Commando points behind the barrels timing cover to sell, please let me know.
 
NORTON HEAVY TWIN
TIMING COVERS
"These are all twin chain timing covers until 20M3S/Commando which become a single chain cover
These two types are not interchangeable"

See link below for inner and outer cover photo views for reference.

"Last cover prior to commando, 650 and atlas 20M. Now with a round mounting surface for the tach mount. normally with a more upright cable but sometimes with a reoriented drilling for a forward tilt of the cable."

"First commando timing cover for 20M3. Still cam end tach drive.
However the biggest difference is the over pressure venting back into the engine block to the oil pump inlet."

"This is a repeat of the 25186 cover but has a very small identifier difference. This cover was on a later 20M3 engine that had evolved to include a lowered timing chest drain."

"First cover for the single chain family 20M3S + commando pn 06-1073 it has the ignition points and AA unit on the end of the cam."

"MKIII commando cover, Timing chain check hole/plug, integral antisump check valve. Over pressure relief vents inside timing chest like first nortons. There may have been a few other engines that used this cover, specifically if the normal commando OPV flow passage was not fully drilled back to the oil pump input."

 
Thank you all for your response. SteveA guessed my purpose only I was going to use a BTH K2 replica.

Ed
 
APRRSV said:
Thank you all for your response. SteveA guessed my purpose only I was going to use a BTH K2 replica.

Ed
Click to expand...
Is a BTH K2 a true magneto, or just an EI inside a K2F replica body?

Sorry to wander off the thread trail.

Slick
 
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