Combat fixes

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I have a (possibly) stupid question.
-My combat (210xxx) was bought 1 year ago.
20k miles (but god know how many she really did)
Starts at first kick (yes she does -always... yes, I am serious)
Runs great, 6000+ rpm.

I never opened it. so dunno if it got superblend.

Do I take that for granted or shall I open it up to improve my chance of survival in the long run?
(you know if I open it it'll never run the same -'if it aint broken don't fix it'...)
 
Nortiboy said:
rx7171 said:
rx7171 said:
Since my bike is a 72 Combat that had sat since 1977 I felt I needed to go into the case to confirm the bearings were superblends.
Since the oil pickup problem that OldBritts suggest maching the case for is for sustained running of the engine at rpms above 4,500 and I never intend to do so
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Click to expand...

Gooday rx7171

I have a semi-stock 73 750 with combat breather. Running 10:1 with 98 Octane it snorts. I have Combat breather and added 850 breather with larger holes in the timing case, all to a bottle. Have done extended cruising (1600 miles) at 5500 rpm (100miles at 6500rpm) with no ill effect and no oil pickup issues. Bottle is always dry. I wonder what the issue is ?
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As I understand the 73 shouldn't have the oil pick up problem like the 72 since the case in that area is different.
Correct me if I'm wrong guys.
If that is the case there should not be any particular reason that oil would be pushed up your breather into the bottle.
If oil stays in engine and oil tank sounds good to me.
100 miles at 6500 rpm is way beyond how I'll treat bike my since that will probably put me up around 105mph with my 21 tooth sprocket and without a fairing or windshield my arms will get tired just hanging on. :shock:
 
Gooday rx7171

I have a semi-stock 73 750 with combat breather. Running 10:1 with 98 Octane it snorts. I have Combat breather and added 850 breather with larger holes in the timing case, all to a bottle. Have done extended cruising (1600 miles) at 5500 rpm (100miles at 6500rpm) with no ill effect and no oil pickup issues. Bottle is always dry. I wonder what the issue is ?[/quote]

As I understand the 73 shouldn't have the oil pick up problem like the 72 since the case in that area is different.
Correct me if I'm wrong guys.
If that is the case there should not be any particular reason that oil would be pushed up your breather into the bottle.
If oil stays in engine and oil tank sounds good to me.
100 miles at 6500 rpm is way beyond how I'll treat bike my since that will probably put me up around 105mph with my 21 tooth sprocket and without a fairing or windshield my arms will get tired just hanging on. :shock:[/quote]

Looks like I can answer my own question. Should have done it earlier but I went to OldBritts site and it appears until the 850 came out the oil return problem that started in 72 should also be in the 73 750's.

>>This Technical article deals with solving the oil pressure loss on the Norton Commandos with crankcases without a sump drain plug. The pressure loss is due to the engine wet sumping at constant high revs. The wet sumping is caused by a poor oil scavenge design on the 1972 750cc engines and was corrected on the 1973 850cc engines. The fix is to modify the crankcases to scavenge oil correctly. This fix involves splitting the cases, which is the hard part, for the actual fix is quite simple. << http://www.oldbritts.com/ob_start.html
 
6500 rpm is actually beyond the rated continous cruise rpm for an 850.
What was it for a 750 ?
 
Orsonoce said:
I have a (possibly) stupid question.
-My combat (210xxx) was bought 1 year ago.
20k miles (but god know how many she really did)
Starts at first kick (yes she does -always... yes, I am serious)
Runs great, 6000+ rpm.

I never opened it. so dunno if it got superblend.

Do I take that for granted or shall I open it up to improve my chance of survival in the long run?
(you know if I open it it'll never run the same -'if it aint broken don't fix it'...)
Click to expand...

Not to hyjack but we're generally in the ballpark.

I am inclined to believe the those are not the original cases and if not, it would be safe to say the upgrades are in place. Don't mean to pry but just how number matching is the unit? Frame, gearbox, crankcase. FWIW I think Combats ended in the 209xxx range. LAB? You there?

Don't get me wrong here, I am not saying yours is not a Combat. As with mine, it is what i make it to be. And I do not mean to deny the the purists, they have there place, to give the rest perspective and a base of control.
 
are you saying the Britts modification does not work ? or are you saying there is another alternative?
 
pvisseriii said:
FWIW I think Combats ended in the 209xxx range. LAB? You there?
Click to expand...

According to factory service release N.3/23, no further Combats were built from serial 211110 (although 32mm carbs still continued to be fitted).

R&M 6/MRJA30 "Superblend" bearings were fitted from 211891 (service release N.2/9) however it's likely that any surviving Combat engine would have had it's bearings replaced by now.
 
there is a better way than butchering the weir out. I have shown this several times but if you like PM me and I will show you how. this along with leaving the breather at the stock position and using Jim Comstoc's reed valve is a better way to do this.

madass140 said:
are you saying the Britts modification does not work ? or are you saying there is another alternative?
Click to expand...
 
are you saying the Britts modification does not work ? or are you saying there is another alternative?
Click to expand...

Instead of removing baffle rise and opening up oil drain in internal passage below, just drill small screen like holes In TS case and let oil flow around the baffle which only goes half was across ending at case seam. JBWeld the front hole.

Its educational to start a Cold Combat that sat for proper wet sump while peering into oil tank, but don't rev up much till the pencil thick jet of secondary oil return tappers off.
 
Seems like its time for a sump screen mod for the Combat case...
 
"Instead of removing baffle rise and opening up oil drain in internal passage below, just drill small screen like holes In TS case and let oil flow around the baffle which only goes half was across ending at case seam. JBWeld the front hole."

Bill, is this still considered butchery.?
 
here is the way I prefer.

Combat fixes


Combat fixes


do the pick up like this ( holes are .109) and plug the original pickup at the front and you have a strainer of sorts along with the weir so you are not forcing oil up the breather hole from crank rotation. so in simple terms IMHO it is not butchery.


madass140 said:
"Instead of removing baffle rise and opening up oil drain in internal passage below, just drill small screen like holes In TS case and let oil flow around the baffle which only goes half was across ending at case seam. JBWeld the front hole."

Bill, is this still considered butchery.?
Click to expand...
 
Windy, I seem to be the only one here with "hybrid" pickup mod. As you know, my baffle was removed per "old Brits"in TX, but after you opened the cases you drilled the passageways and eliminated the rear breather....should I be concerned about future performance, reliability or ???
 
"do the pick up like this ( holes are .109) and plug the original pickup at the front and you have a strainer of sorts along with the weir so you are not forcing oil up the breather hole from crank rotation. so in simple terms IMHO it is not butchery".

So one modification to the cases is considered butchery, yet another similar modification to the cases is not considered butchery?
boy I'm confused.
 
Its less butchery the least modified way is all. Neither shows outside or weakens to matter and neither is ie needed till you've hardened your heart to the blacksmiths inside driving ya forward suddenlly harder the faster ya go, then engine becomes pressurized and also elasticized rubbery flexy character that snots oil out every hot pore and seam. There is a definite need to protect the oil pump when stuff lets go and drilled holes are better solution than oil screen that could get swiped off by a rod nut or barrel piece or piston chunk to add to recovery trauma.
 
Only if you have lived through a combat oil pump blow up as I have, can you appreciate the difference between butchery ( inoa mod or ole brit) which will still allow eating the combat thrust tab or other big bit. The mod I do uses even smaller holes than Windy and lower the oil level even more but will not allow a tab or other bit to lock up and break the pump. My pump died from a breaking up intake valve spring not a tab so removing the tabs is not the cure....Some people do have the intellectual capacity to tell the difference.


madass140 said:
"do the pick up like this ( holes are .109) and plug the original pickup at the front and you have a strainer of sorts along with the weir so you are not forcing oil up the breather hole from crank rotation. so in simple terms IMHO it is not butchery".

So one modification to the cases is considered butchery, yet another similar modification to the cases is not considered butchery?
boy I'm confused.
Click to expand...
 
I had never seen the discussion on the sharp cutter used on the combat cases before. Goes to show you, just because you think we are running in circles here, they apparently change orbit enough to cover some new ground once in a while. That or I am like an asteroid wandering thru the path...

Russ
 
I have my cases (750/#207446) apart and looking at this c/case modification... I wont be racing apart from the occasional squirt here and there...

Is this mod suited for "racing only" or is it a valuable mod to do whilst in c/case???


bill said:
here is the way I prefer.

Combat fixes


Combat fixes


do the pick up like this ( holes are .109) and plug the original pickup at the front and you have a strainer of sorts along with the weir so you are not forcing oil up the breather hole from crank rotation. so in simple terms IMHO it is not butchery.
Click to expand...
 
Yep sir in case stuff comes apart before the pump it helps to limit particle size the pump chews up before seizure. Can add a few more holes on TS case floor too. Good ole JBW works a treat to plug front drain. Its good to do for less oil mess on any Combat that gets run into 2S wake up zone even if not topping and holding on like hard hearted racers.
 
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