New member with a power problem!

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Hi Guys, Just joined the site, great forum and great site. Hopefully some one out there with loads more commando experience may be able to help me.
Recently got my first Commando.............850MK3 She looks great, in need of a little TLC but pretty good. However,i have a problem with her that one of you guys maybe able to help me with.When i got the bike i noticed that it started easily but i couldn't get it to tickover it seemed to run ok upto about 4000 rpm but then didn't want to rev any more, even in 2nd gear, seemed really laboured. The bike still had the original black airbox, the carbs were jetted to original spec, but had peashooters fitted.I checked the carbs and they were Knackered, I decided to replace the carbs and fit an earlier type airfilter in the hope all problems would be cured. Les Emery at Norvil jetted them for me. I fitted them and sync'd them. She now starts, 1st or second kick and ticks over fine when warm.She rides ok up to about 4000 but still won't rev freely when you try open her up, the engine "deepens " but not a lot happens, I get no popping or banging or anything else, she just doesn't seem to have any power. Timing has been strobed and is fine, jets and needle position have been adjusted and changed, I've fitted new wires from the Boyer pick up to the control box , new plugs but all to no avail. Would appreciate any help at all.
 
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I wonder if the valve timing is correct? Unlikely to be at fault I suppose but reminds me of a friends Vauxhall Astra a few years ago, wouldn't rev beyond about 3000 rpm after she'd let someone replace the timing belt, I found it was one tooth out!
 

L.A.B.

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Could be the infamous MkIII soft camshaft syndrome?

Do you know if the camshaft is the original or not?

Have you measured the amount of valve lift on all valves?

If one (or more) of the valves shows significantly less lift than the others, then one (or more) of the cam lobes could be badly worn?
 

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Hi L.A.B. haven't had bike long,was hoping it was something simple like coils or something else electrical.haven't had any covers off yet so haven't checked valve timing, but i do suspect they are the original camshafts. Whats a simple way of checking the valve lift, and what should it be.
P.S. are you the same L.A.B. as i see on the triumph bonneville site. I also have a T140D which i'm lust putting back together.
 

L.A.B.

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JOHNO23 said:
Whats a simple way of checking the valve lift, and what should it be.

Setting a dial gauge up on each valve top collar parallel to the stem would be the normal way to do the check.
If one or more of the cam lobes has worn badly, and I'm not suggesting that it definitely is the problem, but many MkIIIs did have soft camshafts that wore quickly then you may be able to notice any apparent lack of lift without a gauge?




JOHNO23 said:
P.S. are you the same L.A.B. as i see on the triumph bonneville site. I also have a T140D which i'm lust putting back together.

Yes, that's me.
 

L.A.B.

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Figures quoted from the factory 850 MkIII manual:

"Valve lift

Inlet & Exhaust 0.375 in. (9.525mm)"
 

ML

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Not revving beyond 4,000 RPM is a classic sign that the timing chain is one pin out, 9 not 10 on the marks. Seen an identical situation recently on a 750 where the carbs, pipes, compression, valve gap, ignition timing was alll perfect. Last thing of course that was checked was the timing chain.

Mick
 
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Thanks guys, but just checked the valve lift as suggested by l.A.B. and i think he was right........................very little opening of 3 of the 4 valves.
So it looks like the camshaft is knackered............Winter rebuild on the cards !!
 

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Oh well, sorry to hear that.

I also have the same job to do, as I recently took the head and barrels off my MkIII, and a couple of the cam lobes and followers are wearing.
I know it's not the original camshaft, but I've no idea how many miles it has done.



Anyway, how's this for a worn(!) camshaft!:

http://www.norton850.com/camshaft.htm

Amazingly, the engine still ran!
 
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Wow!!! :shock:

The cam on my MkIIA was showing about .060" wear on a couple of lobes, so its gone to RGM for a re-grind.
The odo was showing 11K, and I suspect its genuine. The followers are in pretty good shape by comparison.

New member with a power problem!


Were there any batch issues with cams, or were they all made from cheese!? :roll:

Must do wonders for the fuel economy!
 

L.A.B.

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B+Bogus said:
Were there any batch issues with cams,

Apparently so, I don't know if that is entirely true or not, but the late models seem to be the worst affected?
 

maylar

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Well.. I don't feel so bad any more. This is the factory cam from my '74 MKII after about 35000 miles. I was blaming myself for this (oil problems) until I saw this thread.

New member with a power problem!
 
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