Who made these barrels?
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RennieK said:
750 "short stroke" engines were basically 850 engines with a shorter stroke, what would be the point in "short stroking" a 750 engine, as it wouldn't be a 750 any longer.
http://www.classicbike.biz/Norton/Broch ... LineUp.pdf
Cylinders pulling off the base flanges can be a big problem in single cylinder engines, especially when taken out to bigger oversizes. Maybe this owner has had this happen, and wasn't going to have it on a 750.
And Nortons thru-bolted the heads in 850s to solve pulling all the base studs out, as Dunstall 810 owners were more than aware of, so cylinder problems weren't unknown.
Interesting but...
P.S. What is the count of fins on this ? Is that otherwise a std 750 cylinder ?
It could be interesting to noise test this, may be quieter than std ?
Although an unlikely reason for the modification.
And Nortons thru-bolted the heads in 850s to solve pulling all the base studs out, as Dunstall 810 owners were more than aware of, so cylinder problems weren't unknown.
Interesting but...
P.S. What is the count of fins on this ? Is that otherwise a std 750 cylinder ?
It could be interesting to noise test this, may be quieter than std ?
Although an unlikely reason for the modification.
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I think racers know of this well enough ...
I was pit crewing for a norton racer in the early 90's. By that time he blew up plenty of 750 barrels. They could NOT run 850's and +40 (750) were the limit for the class rules but the barrels became rather tender at that point. This kind of mod I guess was a type of bandaid... and yes, not unheard of.
I was pit crewing for a norton racer in the early 90's. By that time he blew up plenty of 750 barrels. They could NOT run 850's and +40 (750) were the limit for the class rules but the barrels became rather tender at that point. This kind of mod I guess was a type of bandaid... and yes, not unheard of.
I didn't think that one through very well, it seemed shorter when I looked at the photo. I don't think you could add a through bolt there either because the head bolts pretty close to that area at the top. The 850's used the same case bolt pattern and that's not the thickest spot on the cases to add an extra set of bolts. Must be what everyone else has surmised and just be to hold the flange together.L.A.B. said:
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750 barrels cracking at the base is common on 750s if they are raced , bored more than .040 or sleaved. I have several cracked 750 barrels on my shelf. Looks like someone made a through bolt 750 barrel to fix it.
I always just sleaved 850 barrels down to 750 to go racing. Jim
I always just sleaved 850 barrels down to 750 to go racing. Jim
Brooking 850
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Poor you inheriting someones' attempt at a quick fix, looks like they didn't even take the barrels off!!
Get another set
Regards Mike
Get another set
Regards Mike
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I did this mod on the 750 i was racing to convet to bolt through 850 style. The threaded posts are machined from close grain cast iron to match the expansion rate of the barrels and threaded through the fins to spread the load over a wider area. worked well at 11.5:1 cr.
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comnoz said:
I always understood that the problem was caused by lack of maintenance, specifically not tightening the base nuts after every race.
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pommie john said:
That may be part of it, but they do get pretty weak when they are bored oversize. The cracked barrels I have were not from racebikes but they certainly may have been abused. I have one cracked .040 over and one .060 over plus I have a sleeved barrel that cracked when it was being torqued before it had ever been started. I don't try to sleeve 750 barrels anymore, that one didn't taste too good. I worry when they get to .060 oversize. Jim
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I have seen quite a number of 750 barrels over the years where the flange either showed a crack or had parted company with the barrel. Not sure if all of these were bored oversize, which will obviously weaken them, but nearly all of these were off normal road bikes, not racers.
On my race bike I use one of the barrels that look like 850s (i.e. with through bolts), but are to 750 spec (part# 06-1705)- remember the head bolts are also in slightly different positions on 750s to 850s. These barrels are about to be available again from Andover Norton- should be finished within this month, together with the new batch of 850s (part# 06-5074).
Another pro- at least for racing- is, that the more solid barrel, bolted to the naturally fragile crankcases, acts like a "stiffening kit" for the crankcases, which is a good thing especially in a race engine developing a lot more horses and torque than a road engine. Then again, it doesn't hurt on a road engine, either!
Joe Seifert
On my race bike I use one of the barrels that look like 850s (i.e. with through bolts), but are to 750 spec (part# 06-1705)- remember the head bolts are also in slightly different positions on 750s to 850s. These barrels are about to be available again from Andover Norton- should be finished within this month, together with the new batch of 850s (part# 06-5074).
Another pro- at least for racing- is, that the more solid barrel, bolted to the naturally fragile crankcases, acts like a "stiffening kit" for the crankcases, which is a good thing especially in a race engine developing a lot more horses and torque than a road engine. Then again, it doesn't hurt on a road engine, either!
Joe Seifert
The fin count is 8, and the crankcase has been welded back together at the front drive side were the 2 halves join,I guess after cracking. This crankcase cracking happened to my last combat engine in 1975! only at the rear of the barrel after taking the bolted flange with it! luckily i worked in the aerospace trade with excellent welding contacts.
I am reluctant to lift the head as the engine runs ok, if a bit lumpy at tick over. hot cam??ex racer? :?:
I am reluctant to lift the head as the engine runs ok, if a bit lumpy at tick over. hot cam??ex racer? :?:
I looked at a semi-basket, well-used proddie racer once. It had a cylinder that was converted to through-bolts with recesses plunge-milled into the head to give clearance for the bolt-heads....
If the motor runs well you should be happy and just use it with the peace of mind that you may be able to worry less about cylinder problems while you are beating on it. Someone went to some trouble to get it to that point....
If the motor runs well you should be happy and just use it with the peace of mind that you may be able to worry less about cylinder problems while you are beating on it. Someone went to some trouble to get it to that point....
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