COMBAT CRISIS PART 2

I've put about another 5000 miles on the bike this year, riding to work. after flushing the engine out with kerosene (poured in thru the rocker box, then turning by way of the kicker), & freeing up the rings in the RT cylinder ( low compression & smoking), i am satisfied that for now it is sound enough. But as i said, after reading some stuff about soft cases, main brgs, camshaft bushes, & the like, i'm not syre how many miles it has left in it.
the 750 Triumphs that i am more familiar with seem to hammer on quite well & have seen one unit with over 40,000 on the clock, so said to be original miles on an un-split set of cases. is it the general opinion that the combat will go this far?,
or do i need to drop $5000 on a fresh rebuild to get rid of the gremlins?

recklessridr said:

I've put about another 5000 miles on the bike this year, riding to work. after flushing the engine out with kerosene (poured in thru the rocker box, then turning by way of the kicker), & freeing up the rings in the RT cylinder ( low compression & smoking), i am satisfied that for now it is sound enough. But as i said, after reading some stuff about soft cases, main brgs, camshaft bushes, & the like, i'm not syre how many miles it has left in it.
the 750 Triumphs that i am more familiar with seem to hammer on quite well & have seen one unit with over 40,000 on the clock, so said to be original miles on an un-split set of cases. is it the general opinion that the combat will go this far?,
or do i need to drop $5000 on a fresh rebuild to get rid of the gremlins?

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Speaking from my experience in the last 12 years with current combat....would not expect the engine to go 40,000 miles without some up keep. I replaced rings after 20,000 and had a left exhaust guide come loose and repaired. Total on mine is now 46,000, that's 6,000 on the new rings and less on the new valve. Everything running great with the exception of trying to sort out some detonation issues. Combat engines really need superblend main bearings for the engine to last. If your's is early production would not have been so fitted from the factory.

The patent plate on the steering head says it was manufactured in JULY 72. ( all matching numbers, by the way.) It was oringinally sold in binghamton, n.y. i know the guy who bought it as new. i don't yet know how to determine the issue of the main bearings, but i'll try to keep up with you guys on the forum.

Your machine could have had superblend main bearings from the factory since it's pretty late in the production year which ended in September '72. This is the single most important improvement to keep a combat from self destructing. Most of the combats that blew , went by 5,000 miles from what I remember. When I bought mine in '97 it had been sitting for 20 years with 20427 miles on it. Mine was Dec '71 build, so was not supplied with the good bearings although by the time I got it had these. Still needed to replace them during the restoration as the reason it was laid up so long was a left piston collision with the exhaust valve and metal parts all through the bottom end.

Combats also came with a 19 tooth gearbox sprocket. Change this to a 21 tooth to keep the RPMs down. Surprisingly my first Combat (nearly new in '73) got wrung out by me at age 20. Right at 7,000 RPMs the engine had a strong surge from the combat cam, so I regularly pushed it into the red. No, it never blew. At least not with the first 5,000 miles I owned it.

" illf8ed"---
i usually don't push the bike too hard, rarely seeing more than 5500 maybe 6000. im content to ride at a good crusing speed of 67-70, where it seems to smooth out. that's not to say it hasen't redline a time or two, or a sustained 100mph blast down the 4 lane ( did i really write that outloud?) for 30 or 40 miles. it would be nice to know that it's gonna keep me going to work if ridden modestly for another year. that will give me a bit of time to sort some of this stuff out & budget the necessities.
I did go out & check the drive sprocket. looks like both front & rear will need to be replaced this winter, as they both seem a little " angled" & the teeth are getting sharp! as you said 19 teeth.
when the tech digest comes in, do you know if it will reference the serial number to show if superblends were issued on this engine or any other important matters? i rode the thing all summer long, & dont want to screw it up by running it further. with the miles on the clock when purchased, plus what i put on it, it now shows 10,328 miles. the top end seems to be in order, as this thing gives me better than 70mpg, with a finiky rt side carb. now that it is gonna be parked for the winter i would like to get it just a little closer than it is to ease my mind.

recklessridr said:

when the tech digest comes in, do you know if it will reference the serial number to show if superblends were issued on this engine or any other important matters?

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I don't know if you missed my reply in your other thread, or you have chosen to disregard what I wrote, but the information I gave was taken from a copy of the Norton factory service release (N.2/9) detailing the change of bearing type to R&M Superblends which occurred at engine number 211891.

illf8ed said:

Your machine could have had superblend main bearings from the factory since it's pretty late in the production year which ended in September '72.

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As far as I'm aware, the factory updated their model range when it was convenient, or whenever they considered it was necessary?

I'm unaware of any reference to "September '72" being the end of that year's production?

L.A.B. said:

illf8ed said:

Your machine could have had superblend main bearings from the factory since it's pretty late in the production year which ended in September '72.

Click to expand...

As far as I'm aware, the factory updated their model range when it was convenient, or whenever they considered it was necessary?

I'm unaware of any reference to "September '72" being the end of that year's production?

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Normal model year production ran from Oct of the previous year to Sept of the current model year...in plan. In practice there was overlap. I have copies of factory records with model year 151xxx built in Dec 71 and have owned 201123 '72 combat built Oct '71 and currently own a Dec '71 built '72 combat. Updates within model years occurred as was convenient or necessary as you say.

illf8ed said:

Normal model year production ran from Oct of the previous year to Sept of the current model year...in plan. In practice there was overlap.

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In that case, I'd have to say there must have been a great deal of overlap?
As examination of the Commando model range certainly doesn't appear to show evidence of there being a regular period within the calendar year for introducing new models or new 'mark' numbers?

750cc
Original Commando 4/68-3/69
750 R 3/69-9/69
750S 3/69-6/70
Fastback 3/69-8/70
Fastback MkII 9/70-12/70
Fastback MkIII 1/71-12/71
Fastback IV 1/72-3/73
Fastback LR (Long Range) 4/71-12/71
Fastback LR MkIV 1/72-2/73
Roadster 3/70-12/70
Roadster II 1/71-12/71
Roadster IV 1/72-2/73
Roadster V 3/73-10/73
SS (Street Scrambler) 3/71-10/71
PR (Production Racer) 4/71-10/73
Hi-Rider 5/71-12/71
Hi-Rider IV 1/72-2/73
Hi-Rider V 3/73-10/73
Interstate 1/72-2/73
Interstate V 3/73-10/73
850cc
Roadster MkI 4/73-12/73
Roadster MkIA 9/73-2/75
Roadster IIA 1/74-2/75
Roadster III 2/75-9/77
Interstate MkI 4/73-12/73
Interstate 1A 9/73-2/75
Interstate IIA 1/74-2/75
Interstate MkIII 2/75-9/77
Hi-Rider MkI 4.73-12/73
Hi-Rider II 1/74-2/75
750cc/850cc
John Player Replica 11/73-2/75

L.A.B. said:

In that case, I'd have to say there must have been a great deal of overlap?
As examination of the Commando model range certainly doesn't appear to show evidence of there being a regular period within the calendar year for introducing new models or new 'mark' numbers?

Click to expand...

What advise would you give to our new viewer related to longevity of his combat?

illf8ed said:

What advise would you give to our new viewer related to longevity of his combat?

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The bearings could have been changed at some point in the bike's history, who knows, but as I see it, recklessridr has two main choices. My advice to him would be that he could either continue to ride it, using a reasonable amount of restraint where max. revs are concerned, which he appears to be doing,-until such time the engine shows signs that the main bearings are in need of replacement? Or he inspects them as soon as it is reasonably practicable for him to do so, as then he would at least know either way if they are R&M or FAG (if R&M 6/MRJA30 then they should be changed for the FAG type) bearings in there, or not?

When I was a kid, maybe 71 ish? My dealer was calling all Combats back for the upgraded bearings. A few of the heavily ridden bikes had blown up if I recall in our area. Did Norton issue a general recall on the Combats to rectify this issue?