Do you spin your stock Commando over 8,000 RPM?

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grandpaul

grandpaul

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Everyone who REGULARLY runs your BASICALLY STOCK Commando at 8,000 RPM for significant periods of time (extended highway runs) under load, please report back.

I'm not talking about the time your throttle cable stuck and you saw the tach go over 8,000, or the time you were flying down a long mountain pass and saw the tach cross 8,000; I'm talking about REGULAR runs over 8,000 for more than 5 or 10 miles at a time.

I'm also not talking about lightweight pistons and aftermarket rods and/or aftermarket/reworked/welded cranks, JUST BASICALLY STOCK ENGINES (typical carb mods, headers, electronic ignition, even belt drives okay)

My guess is there will be an EXTREMELY short list of respondents in the affirmative...
 
The valves float on my stock MK3 before 8,000 rpm. That would keep me out of this club, even if common sense didn't.

Ken
 
Would it also be safe to say that you are NOT talking about 4th gear either.
 
There is a very big difference between talking about cruising for hours at +8000 rpm, and claiming the crank will blow if you get there for 2 seconds.
Unless you have tested these claims yourself, personally ?

Also seems pretty useless switching threads at the drop of a hat, without giving the background discussion to where the thread is coming from.
Or going to.

Owners Manual says rpm redline is 7000 rpm.
850 manual says not to do extended periods of over 5800 rpm.

Factory race bikes reportedly gave max power at 7800 rpm. ?
(Perhaps that was the short stroke version ?)
If they only revved to 7000 though, that doesn't make them any better than a stock streetbike...
 
Owners Manual says rpm redline is 7000 rpm.
850 manual says not to do extended periods of over 5800 rpm.
Click to expand...

given that, WHY would anyone be DUMB enough to exceed those limits with the STOCK motor?
 
Ask GP , its his question.

And his claim that the crank will blow in 2 seconds if you do this.
Can't say I've heard this one before.
With probably no intention of experimenting to find out....

Didn't the tops pull off early type Commando pistons sometimes, without even exceeding redline ?
 
I have no intention of experimenting to find destructive limits of ANY engine.
 
Rohan said:
Also seems pretty useless switching threads at the drop of a hat, without giving the background discussion to where the thread is coming from.
Or going to.
Click to expand...

Exactly as I figured, this discussion has no business clogging up other people's threads.

Statements were made that are, on their face, absurd.
 
My old 850 crank is modified according to the JS race manual (lightened and with radiused PTO shaft). I used to race this crank and have tested the 750cc lightweight JS pistons, longer rods, beehive springs, radiused cam kit with lightweight lifters etc up to around 8200 RPM. with no valve float or any other problems.

Doesn't mean that I recommend doing this. And certainly not with stock components.
 
I always try to change on my 850 before 7,000 RPM, however always see 7,500 for an instant. It hasn't gone bang yet but it is a bit nail biting . I find gearing the torquey motor difficult. I've got a set of cases which are cracked through the drive side main, and I've welded and shrunk a plate to fix them. The kid who did that used to race against the four cylinder Japanese bikes along the Great Ocean Road on sundays, doing really stupid revs while the motor had the standard balance factor. Triumph 650 motors will cop 8,000 revs reliably without the valve gear tangling , so the Norton valve gear can probably be made to stand up. But that Norton crankshaft whizzing around at 8000 rpm out of balance is a worry.
 
Back in 1973-ish I bought a new Commando 750, 3rd one, which naturally blew it's bottom end to shit within the warranty period. I was gunning it in 3rd gear merging onto the hi-way almost at red line when both big end's farted and crapped themselves.
One rod end totally vaporised, I couldn't find any trace of the bits, but the other maintained a representation of an oblate ellipsoid.
The crank didn't seem to be rooted but then I was so pissed off I couldn't have cared less. I could see it clearly through the rather large hole in the case that the rod's made.
Thankfully the clutch took the hit and I was able to fight the damn thing to a safe halt on the road side.
 
grandpaul said:
Statements were made that are, on their face, absurd.
Click to expand...

Go read the old roadtests of the Combat 750 then.
Several mention they saw in the region of 8000 rpm in the lower gears on test.
The Combat is listed as max power at 6800 rpm - the the tacho had no redline marked on it (was that the model like this ?).
Engines don't generally run of of puff/revs right on redline...

Tthe 850 is listed as max power at 5800 rpm.
And several tests mentioned it felt like it was cammed so it wouldn't even reach the marked redline of 7000 rpm, power drops off noticeably on the dyno much over 5800 rpm.

No-one said anything about cruising in top gear at 8000 rpm + ??
- that would imply something was seriously undergeared, or someone was on a rocketship.

The Combat had a history of being a bit of a grenade, for various reasons.
It wouldn't be a legend if it hadn't...
 
Throber said:
Back in 1973-ish I bought a new Commando 750, 3rd one, which naturally blew it's bottom end to shit within the warranty period.
Click to expand...


How many miles had it done. That would be within the 3 months ?

Did you get a new motor under warranty ?
1973 would be almost past the Combat era ??
Or does the -ish cover Combat models..!
 
All both of my '72 combat's have/had a redline on the tach. The first was new in '73 although an early example 201123. That one got spun beyond 7,000 regularly, but I don't remember sustained running at 8,000. I never blew and never received superblend bearings up to 5,000 miles when I sold it. I was 20 years old then so consider it was spun like a Honda.

Do you spin your stock Commando over 8,000 RPM?
 
Ha, I don't keep a diary mate. I can't remember the miles, not that anal.
It was a black Roadster. I took it back to the shop, they put a new motor in it. I put it on their shop floor and they sold it off on my behalf. It took ages to get the new motor then they charged me huge vig for the sale. Never went back to them after that.
Turned to Jap bikes and never looked back. Had lot's of them.
Then I bought this 850 Hi Rider in a fit of nostalgia. Turns out to be a mistake.
ish means ish ! Means I can't remember exactly-ish. ish-that OK with you ?
Lot's of questions !
 
No worries mate. It was a sad history for me as a young dude trying to enjoy Brit bikes while the industry was in it's death throw's.
I love Commando's for some reason. Wish I could work out why.
 
Then I bought this 850 Hi Rider in a fit of nostalgia. Turns out to be a mistake.
Click to expand...

so Throber, ok I can see maybe not liking the Hi Rider's tank, seat, or sissy bar....

but other than that it ought to be a decent enough Commando

so how come you don't like it, that it turned out to be a mistake?
 
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