1972 750 Commando cam timing

Status
Not open for further replies.
P

Piggy

Joined
Mar 13, 2022
Messages
1
Country flag
Thanks for the approval to site
Be gentle peoples and talk to me as if I was five I’m a newby to this world of motorcycle repairs and re builds
I’ve replaced my timing chain and as per manual have set LH piston to TDC ( compression stroke) and lined up all gear markings with ten rollers between the intermediate and cam sprockets
When I find TDC on the RH cylinder all markings are now at 180 deg different
Is this correct TIA
 
At T.D.C. , the overlap ( both near their seat , inlet closing , exhaust opening ) should be about even , each side .

1972 750 Commando cam timing


As in , get it at T D C , turn till say inlets closed , then ditto Exhaust ( the other way ) . Normally say 3 Deg. Lag .

1972 750 Commando cam timing


A cheapp protractor makes a good degree wheel . Tho hard plactic can split , drilling it . Go real slow .

A 3 foot diameter degree wheel , and you can get real accurate measurements . Comparitive however

IS FINE . If you have three hands , the 'grab 'on a feeler guage gets reliable figures .
 
Last edited:
The way you replaced the cam chain is, indeed, by the book and works just fine. If you want to get deeper and have the better part of the a day you can check the cam timing as mentioned above; quality advice guys. I do this while building an engine before bolting on the head, but can be accomplished as described above.

Where I'm going with this is that moving the cam chain 1 pin on the will advance the timing 15 degrees, moving the pinion gear 1 tooth will advance or retard the cam timing 5 degrees. I tried it and found the endeavor confusing, tedious and of no benefit. I HAD to go through the entire process when I installed a pair of Megacycle cams designed for a 76 degree off-set Triumph t140.

Your work is fine, if I build any more Nortons I'll do it by the book.

Best
 
Piggy said:
Thanks for the approval to site
Be gentle peoples and talk to me as if I was five I’m a newby to this world of motorcycle repairs and re builds
I’ve replaced my timing chain and as per manual have set LH piston to TDC ( compression stroke) and lined up all gear markings with ten rollers between the intermediate and cam sprockets
When I find TDC on the RH cylinder all markings are now at 180 deg different
Is this correct TIA
Click to expand...
‘72 standard Commando or combat engine? I bought my ‘72 combat in 1997 and since put over 40,000 miles on it after complete rebuild.
 
Piggy said:
Thanks for the approval to site
Be gentle peoples and talk to me as if I was five I’m a newby to this world of motorcycle repairs and re builds
I’ve replaced my timing chain and as per manual have set LH piston to TDC ( compression stroke) and lined up all gear markings with ten rollers between the intermediate and cam sprockets
When I find TDC on the RH cylinder all markings are now at 180 deg different
Is this correct TIA
Click to expand...
Camshaft runs at 1/2 crank rotations, so with a 360 degree crank the two 360 TDC's are 180 apart at the camshaft.
 
ILLF8ED said:
‘72 standard Commando or combat engine? I bought my ‘72 combat in 1997 and since put over 40,000 miles on it after complete rebuild.
Click to expand...
Why would that make any difference at all? Or are you just reaching out to a fellow '72 owner? :cool:
 
Matt Spencer said:
At T.D.C. , the overlap ( both near their seat , inlet closing , exhaust opening ) should be about even , each side .

1972 750 Commando cam timing


As in , get it at T D C , turn till say inlets closed , then ditto Exhaust ( the other way ) . Normally say 3 Deg. Lag .

1972 750 Commando cam timing


A cheapp protractor makes a good degree wheel . Tho hard plactic can split , drilling it . Go real slow .

A 3 foot diameter degree wheel , and you can get real accurate measurements . Comparitive however

IS FINE . If you have three hands , the 'grab 'on a feeler guage gets reliable figures .
Click to expand...
This answer is just trying to make life more complicated ;)
 
RoadScholar said:
The way you replaced the cam chain is, indeed, by the book and works just fine. If you want to get deeper and have the better part of the a day you can check the cam timing as mentioned above; quality advice guys. I do this while building an engine before bolting on the head, but can be accomplished as described above.

Where I'm going with this is that moving the cam chain 1 pin on the will advance the timing 15 degrees, moving the pinion gear 1 tooth will advance or retard the cam timing 5 degrees. I tried it and found the endeavor confusing, tedious and of no benefit. I HAD to go through the entire process when I installed a pair of Megacycle cams designed for a 76 degree off-set Triumph t140.

Your work is fine, if I build any more Nortons I'll do it by the book.

Best
Click to expand...
This answer also says yes, but suggests that if you want to, you can really make your life much more complicated, don't! :)
 
Piggy said:
Thanks for the approval to site
Be gentle peoples and talk to me as if I was five I’m a newby to this world of motorcycle repairs and re builds
I’ve replaced my timing chain and as per manual have set LH piston to TDC ( compression stroke) and lined up all gear markings with ten rollers between the intermediate and cam sprockets
When I find TDC on the RH cylinder all markings are now at 180 deg different
Is this correct TIA
Click to expand...
Yes! :cool:
 
SteveA said:
This answer says...... Yes! ;)
Click to expand...
LOL, not quite 100%, we don't precisely know if I gave the right answer as Piggy has not said where he measured the 180 degrees at, hence my answer so he could the 2 measurement points and the different results.
 
BALLS ,
He said he didnt know the THEORY . So a pitchers worf a fousand woids . ;)
something like that . anyway .

checking the OVERLAP is about Top Dead Center ( piston at the top of the bore )
is DEAD EASY . Not to Mention a SAFEGUARD .
Put a stick / Pencil or such ( soft ) like in a plug hole . Plugs Out ! on mainstand .
Put it in 2nd , nudge it over ( the injun ) with the rear wheel . Till PISTON is at THE TOP .
One Cyl both in & ex should be almost nearly but not quite shut , or is it just open .
THERE WILL BE NO SLACK / RATTLE at the rocker arm ends .

Looking at the arms , as you nudge the wheel a bit , one arm will soon free .
whack the wheel gently the other direction , the arm will activate again and the other free off .
this is at the OVERLAP , which is within a few degrees of Top Dead Center . and is pretty bleedy basic .

The Graph Below , illustrates WHY SO ! .

1972 750 Commando cam timing

which shows the OVERLAP on ' 360 ' . about 45 Deg of crank rotation , each side , your on one lobe .

Hence , chuck piston on TDC , Rotate till a arm free . Back . ditto opposite rotation .
About the same Ea Side , youre FINE .
But a 3 degree lead is usefull . If youre getting tecnical .

ALSO , if a New Fit , plugs out . One Rather Gingerly turns it through ( Injun ) a few times .

If it goes C L A N G . & stops , Jams . you may not have it quite right .
Hence a Overlap Check , being simple , is rather a good idea .

1 pin on the will advance the timing 15 degrees, moving the pinion gear 1 tooth will advance or retard the cam timing 5 degrees.
Click to expand...
BUT if you do both , you get 20 ! or 10 , or 5 .
So if its Two Late , throwing one one twooth and the other two , gets 5 degrees , and then its 3 early .

Putting in a miss stamped ( was told was 3S wqhich I assumes a Daytona Cam ) SS - COMBAT ,
this was neccesary .As it was the wrong Cam , after three or four atemps to matcxh In & Ex opening & closing . to specs .
Tearing hair out etc . One more go , The FAARRGH , Bleedy Overlap , Blast Late . Right a tooth here a few there , Overlap
is Just Before TDC ( rather than AFTER ) and of she goes . Like a cut cat . Bar plug readings . Hence COIL posts .

no good Coils , No good plug readings . But thats another story . Tappet Clearabnces are best matched . both inlets .
both Ex . Spot On . For even opening & closing . Not ' near enough ' , ' shes right ' . Eactly even free or drag on feeler .

After All , He is a Kiwi . they normally digest einsteins unified feild theory for breakfast . ;)
 
Last edited:
Piggy said:
Thanks for the approval to site
Be gentle peoples and talk to me as if I was five I’m a newby to this world of motorcycle repairs and re builds
I’ve replaced my timing chain and as per manual have set LH piston to TDC ( compression stroke) and lined up all gear markings with ten rollers between the intermediate and cam sprockets
When I find TDC on the RH cylinder all markings are now at 180 deg different
Is this correct TIA
Click to expand...

The camshaft is keyed to the crankshaft via the mark alignments, the marks set the camshaft to the lobes to suit one cylinder at set up as per the manual. (A default)

If the crankshaft pinion mark is in line with that on the idler gear mark, the idler upper mark will be in the correct location and then it is just the pin count to the camshaft drive sprocket mark. (As you have done)
Rotate the engine one rotation will put the markings as you say 180 away based the camshafts half speed via the drive reduction.
Taking for granted it is a stock factory camshaft and associated driving parts.
 
Matt Spencer said:
BALLS ,
He said he didnt know the THEORY . So a pitchers worf a fousand woids . ;)
something like that . anyway .

checking the OVERLAP is about Top Dead Center ( piston at the top of the bore )
is DEAD EASY . Not to Mention a SAFEGUARD .
Put a stick / Pencil or such ( soft ) like in a plug hole . Plugs Out ! on mainstand .
Put it in 2nd , nudge it over ( the injun ) with the rear wheel . Till PISTON is at THE TOP .
One Cyl both in & ex should be almost nearly but not quite shut , or is it just open .
THERE WILL BE NO SLACK / RATTLE at the rocker arm ends .

Looking at the arms , as you nudge the wheel a bit , one arm will soon free .
whack the wheel gently the other direction , the arm will activate again and the other free off .
this is at the OVERLAP , which is within a few degrees of Top Dead Center . and is pretty bleedy basic .

The Graph Below , illustrates WHY SO ! .

1972 750 Commando cam timing

which shows the OVERLAP on ' 360 ' . about 45 Deg of crank rotation , each side , your on one lobe .

Hence , chuck piston on TDC , Rotate till a arm free . Back . ditto opposite rotation .
About the same Ea Side , youre FINE .
But a 3 degree lead is usefull . If youre getting tecnical .

ALSO , if a New Fit , plugs out . One Rather Gingerly turns it through ( Injun ) a few times .

If it goes C L A N G . & stops , Jams . you may not have it quite right .
Hence a Overlap Check , being simple , is rather a good idea .


BUT if you do both , you get 20 ! or 10 , or 5 .
So if its Two Late , throwing one one twooth and the other two , gets 5 degrees , and then its 3 early .

Putting in a miss stamped ( was told was 3S wqhich I assumes a Daytona Cam ) SS - COMBAT ,
this was neccesary .As it was the wrong Cam , after three or four atemps to matcxh In & Ex opening & closing . to specs .
Tearing hair out etc . One more go , The FAARRGH , Bleedy Overlap , Blast Late . Right a tooth here a few there , Overlap
is Just Before TDC ( rather than AFTER ) and of she goes . Like a cut cat . Bar plug readings . Hence COIL posts .

no good Coils , No good plug readings . But thats another story . Tappet Clearabnces are best matched . both inlets .
both Ex . Spot On . For even opening & closing . Not ' near enough ' , ' shes right ' . Eactly even free or drag on feeler .

After All , He is a Kiwi . they normally digest einsteins unified feild theory for breakfast . ;)
Click to expand...
That would be field :cool:
 
Status
Not open for further replies.

Similar threads

Mark Savage
  • Locked
Slider for TLS query. 1972 750 Commando
2
Replies
30
Views
4,863
Mark Savage
Mark Savage
J
  • Locked
What are 1972 750 Commando Yoke offset
Replies
1
Views
721
baz
baz
J
  • Locked
850 Yoke SET on 1972 750 Commando
Replies
3
Views
920
Jared Hamilton
J
B
  • Locked
1972 - 750 Commando Engine Rebuild
Replies
3
Views
1,207
MikeM
MikeM
Burgs
  • Locked
Rear Wheel Spacers 1972 750 Commando Need Spacer Lengths
Replies
0
Views
778
Burgs
Burgs
Back
Top