Camshaft culprit?

After finishing a nut and bolt restoration (my first) on a dead '72 Commando, my motor runs hot and lacks power. I've gone through the carbs, sorted through the electrics, checked and rechecked the timing to no avail. Today I removed the cylinder head and measured my cam specs with the dial indicator on the pushrods. At .016 puch rod lift, intake opens @49 BTDC and closes @62 ABDC; exhaust opens @70 BBDC and closes @39 ATDC. Max lift is only 260. Standard cam specs measure intake opening @ 50 BTDC and closing @ 74 ATDC; exhaust opening @ 74 BBDC and closing @ 82 ATDC with max lift at 330.

Do my figures indicate a badly worn cam (my interpretation)? Could these specs be responsible for my engine problems?

Thanks kindly in advance for helping.

Bill Walker

Are you setting the valve clearance to .016 with an indicator and than putting the indicator back on to the top collar to do this test? That is what Les at Norvil told me to do to do the initial set up to time the cam in. I don't know if it works for degree-ing in the cam though. Sure sounds like you need a new cam but with wear that severe shouldn't the lobes be way off from each other intake to intake, exhaust to exhaust?

WMW said:

At .016 puch rod lift,

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The 750/850 manual says: "Valve timing (measured at .013 in) cam lift"

Valve lift isn't the same as cam (or pushrod) lift, as the rocker arm ratios need to be taken into account when checking, so as norbsa said, valve lift has to be measured at the valve, as far as I know.

Hi Greg,

I don't know how to set valve clearances - rocker clearances yes. Jim Comstock rebuilt my head and I imagine you're talking about something about the valve seat combustion chamber interface? However for these measurements the head is off and the dial indicator is on the appropriate pushrod.

My initial measurements were for the right cylinder. Left side measurements are: Intake 48/68; Exhaust 62/39. Lift is again 260.

I could put the head back on and remeasure with the dial indicator on the valve spring collars, but am reluctant to go through all that procedure if it looks like I'll end up replacing the cam based on what I'm seeing at the pushrods. Because of rocker geometry I figure the lift at the pushrods might conceivably be less than the lift at the valves (i.e. my 260 lift might wind up being closer to 330).

From your postings on this forum and elsewhere, I feel your mechanical knowledge is peerless. In your opinion is it likely my camshaft is the source of my troubles? As a mechanical newbie and long time klutz the last thing I want to do is split the engine cases, replace the cam, etc., only to find my troubles unresolved.

Thanks!

Bill Walker

Dear L.A.B.,

Sorry I posted prior to reading your reply.

Data at .013: Left intake 51/63
exhaust 74/42

Right intake 51/66
exhaust 72/44

I'm guessing the suggestion is to refit the head and repeat
all measurements at the valve which to me means the spring collar?

Thanks!

Bill Walker

Cam profiles

Hi WMW,
Log onto Dave Comeau's website www.atlanticgreen.com he has posted a number of cam profiles. Maybe you can find some useful info there.

GB

Better be sure the cam timing is correct. I had a bike that was one lroller off and it ran like a dog. This would also cause hot running. You have to count the rollers between the marks.

WMW said:

As a mechanical newbie and long time klutz the last thing I want to do is split the engine cases, replace the cam, etc., only to find my troubles unresolved.

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As you've got the head off already, why not remove the barrels? As then you should be able to see if the cam looks worn? If there is significant wear on any of the camshaft lobes then I'd think you'd be able to see it?


According to the manual, the rocker ratio for inlet and exhaust is: 1.13:1

Do a dry reassembly with the old head gasket the practice will pay off later. Recheck your #'s with the valves set at .016 using the indicator on the adjustment screw than dropping down to the flat spot on the collar near the stem. As LAB points out your .260 is going to be .290 at least, then pull the jugs and have a look at the cam and lifters. Remember that a pro can do a complete motor build in one 8 hr day with good parts on hand and service tools. Even if it takes you weeks it's worth your time.
It's kinda tricky getting a one inch travel dial parallel to the valve stem but once you do checking the valve timing is also worth your time. Commandos are found to be 5 degrees off when on the marks all the time.

Thanks one and all,

Just to update: After reading L.A.B.'s first reply, I re-installed the cylinder head (the motor is still on the bike). I re-measured exhaust valves at the adjustment screw at .013 lift and found right @ 60/28; left @ 61/30 both with 320 lift. After hours of trying I'm convinced it is impossible to measure intake valve parameters with the motor in the frame (at least with the dial indicator I have).

My next move will be to remove cylinder head and barrels to visually inspect the cam. I examined the cam prior to initial assembly and although used, it looked to be in pretty good shape to my novice eye. I counted those camchain links about 10 times before assembly and I positively know the camchain is on correctly - would that it were that straightforward!

It will take me a few days at least to report back as that thing called "work" once again will interfere with my lifestyle.

'Til then,

Bill Walker

All can be as you say Bill. And you could still have a problem with cam timing. The broached key ways, and the machine cut key ways could have you off time. With the indicator set up you have you can check this and know if it's right. Complete the cycle of knowing it's all OK.

Happy holidays and greetings to all,

Just an update. As recommended by Greg and L.A.B., I removed the barrels. The cam lobes looked just fine. Thinking I might have something unusual like a sproket key slip problem, I removed the timing cover, oil pump and cam nut. The cam sproket would not pry off as recommended in various manuals, so I used a gear puller. I succeeded in thereby both removing the sproket and fracturing the end of the camshaft - Unbelievable! - I should film my exploits as a primer in stupidity. The keys/keyways were all fine, of course. I proceeded to remove the motor and split the cases. The now worthless cam was otherwise nearly perfect (330 lift at the cam on intake and exhaust) and I'm left with a torn down cycle and no diagnosis. To paraphrase Thomas Edison, at least I know what's not the problem!

My next plan is to reassemble the motor using an unused Dunstall cam I have (very similar to stock 06-1084 but with 350 intake lift). I'll have to resurface the tappets, of course. I'll check timing, valve lift (dial indicating the valves will be a breeze with the motor on an engine stand), etc., and report back. This will take me a while, but having two Commando rebuilds under my belt (I restored a 69 S along with this '71 Longrange Fastbask), I'm now a seasoned klutz.

Thanks again! I'll update as appropriate.

Bill Walker

WMW, Are you running Boyer electonic ignition by any chance? I had one where the trigger wires were resoldered on incorrectly and consequently the timing when checked was apparently OK, but the advance and other parameters were all screwed up, it ran hot and badly. It is vital on this system that the black and yellow stripes on the trigger wires correspond to the same wires going into the control box.

"I'm now a seasoned klutz."

Bill,

Don't be too hard on yourself. If everyone here were to admit to their unfortunate mechanical exploits, I'm certain this website would crash.

Thirty some years ago, a guy I know quite well, removed the driveside main bearing by pounding it out from the inside of the case of his 69 Commando. That necessitated a trip to a weld shop for case repair. This guy still has a minor bauble now and then. Usually by out thinking himself.

ludwig said:

Anyway , you are a very nice guy , saying 3 times ' thank you ' for a load of bad advice ..

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That's a bit harsh ludwig, as I don't think any "bad advice" was given to Bill by anyone?

Your diagnosis may very well turn out to be the correct one, but Bill seemed fairly certain he had a camshaft problem and had already removed the head by the start of this thread, Bill also chose to ignore your advice -rightly or wrongly.
It was only suggested (by me) that the barrels were removed so that he could do a visible check of the cam lobes. It is unfortunate that Bill broke his camshaft, but it was his decision to continue to pursue what he believed to be a camshaft problem, and you wouldn't normally expect it to break when the sprocket was pulled off would you, but the final responsibility for the breakage must lay with Bill himself, as I think he knows already.

Bill, it seems that you still haven't found the problem. I've no experience with cam timing aspects. Always been happy with mine.

If it were me, I would be thinking about what exactly has been restored / replaced on the motor. I would say that it's fairly normal for a Commando with new mains and a rebore to feel tight and probably a bit hot for 500 miles or so and I certainly wouldn't be trying to extract performance from it.

It might sound obvious but newly painted barrels smell a lot hotter than they are and running a Commando for long while it's stationary will get it all hot and bothered.

Which ignition system are you running ? Is carb and exhaust set-up standard ?

Sorry if you've already checked all this or find it too blindingly obvious for words ! :?

Well this is disheartening news Bill. You sure do have a good attitude about it though. It would not be the first time I have seen worst deeds done over a fouled newish set of plugs. Nothing to do but go on. Can't win ,Can't break even, Can't quit. Always have spare plugs and use them as a tool. Always check that first than the Grounds,then the timing, than the carbs and petcocks. Spark fuel and air.... Spark fuel and air...

ludwig said:

Just reread Bill's first post and his question :
"Do my figures indicate a badly worn cam (my interpretation)? Could these specs be responsible for my engine problems?" (quote)
Here , we all should have answered : "most likely NOT ! , look somewhere else first "
Maybe we did not encourage him to dig deeper in his engine but we didn't stop him either .

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Yes, maybe, although Bill had already said: "I've gone through the carbs, sorted through the electrics, checked and rechecked the timing to no avail." therefore, it was necessary for us to take him at his word that everything else that could possibly have been the cause of the problem had already been checked and eliminated?



And Bill, I hope you soon find out what that problem is, and please would you let us know when you do?

And now for a bit of comic relief:

per Norbsa: "...can't win; can't break even; can't quit" fits perfectly regarding Norton ownership, notwithstanding these are the first three laws of thermodynamics.

Bill, all I can say is that we've all been there, so you're in good company; you'll figure it out and in the end, it will all seem worthwhile.

Take care and happy Holidays!

Greetings all,

Between laughs, let me seriously and wholeheartedly state I remain in awe at the collective mechanical knowledge and experience encompassed on this forum and indebted to all who've taken the time to help me. My mistakes past and future are entirely my responsibility. I regard them as opportunities to learn.

dave M: Initially I tried a Boyer and, in fact, did switch the wires on the backing plate using Greg's Boyer wire repair kit! Eventually I figured that out, but experienced serious kickback issues which resulted in a pretty banged up right foot which took 5 weeks to heal. While recuperating, thorough checkout of battery, electrical connections, Boyer module, timing, etc., revealed no problems. I finally installed a Pazon ignition which cured the kickback.

79x100: The motor gets so hot the headers glow and the timing cover becomes too hot to touch. The carbs are Amal 932s (930s are stock). I have a high output Sparx 3 phase alternator with a solid state regulator/rectifier. Headers are stock 1 3/8" with restricted (i.e. not straight through) mufflers.

Again, thanks to all for invaluable input. And yes, Jason, I absolutely know I'll (we'll) "figure it out in the end" but it's already worthwhile. And L.A.B. you're darn tootin' I'll let you know when that happens!

Warmest regards,

Bill Walker