Why We Badmouth Dunstall 810 Kits

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lcrken

lcrken

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I've been working to repair a Dunstall 810 cylinder for sale to Piero, and thought I'd post some pictures to show why they are such a problem.

Original pictures are here, showing pulled head bolt inserts and oversize helicoils for front studs:

dunstall-810-cylinder-t18897.html

The front stud repair went pretty well. I replaced the 3/8" helicols with Bigserts for 5/16" studs, shown below. They do break through into the push rod tunnels, so require sealing to keep oil from migrating up the studs.

Why We Badmouth Dunstall 810 Kits


The head bolt inserts were more trouble. I had to remove the liner and clean up the counterbore for the sleeve lip, shown here with the liner out and the machining finished.

Why We Badmouth Dunstall 810 Kits


These pictures of two of the inserts with the liner out show one of the reasons some of us aren't so excited by the quality of Dunstall cylinders.

Why We Badmouth Dunstall 810 Kits


Why We Badmouth Dunstall 810 Kits


Still, I think it will be ok to use once I get the liner back in, at least for someone who really wants to restore their Dunstall bike to original (at least as long as it lasts, anyway).

Ken
 
My 750 barrels have had this work done, but as the liners are smaller there was no problem - I guess the 810 kit was pushing the design right to the limit.
OK on first assembly, but not good after a couple of dismantle cycles.
I experienced the issue working on a Range Rover V8. After the heads had been off the second time (due to a head bolt pulling out and the Workshop sending it out to my friend in that condition :shock: ) I helicoiled the lot.

It looks like a good save, Ken.
 
I think people may forget these were ment to be light weight racing parts. They were not realy of road use an never mean to last to high mileage which some of them have now done.
 
Do ya think if the CR was lowered and copper oil ring head sealing added it would extend life of fastener inserts? Also might not want to give it full throttle to approach the 70 hp Dunstall stressed their racers with. I couldn't resist of course.
 
Was the alloy from melted down parking meters or Spitfires or something ?? reading on the Rover K series fours , the alloy can be anealed by overheating ( boiling the motor badly ) turning it to scrap .
 
Matt Spencer said:
Was the alloy from melted down parking meters or Spitfires or something ?? reading on the Rover K series fours , the alloy can be anealed by overheating ( boiling the motor badly ) turning it to scrap .
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It is a fairly soft alloy. Modern replicas like Maney and Robertson are cast from a much higher strength (and harder) alloy, probably the equivalent of US A356 alloy, popular for cylinder blocks and such.

Ken
 
toppy said:
I think people may forget these were ment to be light weight racing parts. They were not realy of road use an never mean to last to high mileage which some of them have now done.
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Really? Back in the early seventies Dunstall advertised these kits for street bike use, and that's how most of them were used. The displacement limits for most classes the 750 twins raced in at the time were 750 cc, so there wasn't that much demand for 810 kits for racing. Dunstall also sold the same kit as a 750, with 73 mm bore, using the same castings but thicker liners, but sold very few of them. I ran one of the 750 cylinders in my race bike for a few races, and it worked all right, although I did have to re-torque the fasteners regularly.

Ken
 
I bought a 810 kit in the late 70s and installed it on my N15. Less than 100 miles, on the third retorque it pulled the threads. I installed long helicoils and they lasted a few more weeks. Then I had a machine shop install long custom inserts. They cracked into the bore and would not hold torque. Then I removed the liners and ground wide grooves that completely removed the original threads and had a welding shop use a heliarc and fill the grooves and then rebored them so the liners would fit again. I cut new threads and used longer bolts. I got a couple months use out of it that time. I got the feeling they were cast from old Amal carb bodies. Jim
 
"I got the feeling they were cast from old Amal carb bodies. Jim"
exactly, had they been cast out of something like A356 then maybe they would of had a better lifespan, I have a couple of 810 cylinders and doubt that I'll bother trying to fix this problem.
 
madass140 said:
"I got the feeling they were cast from old Amal carb bodies. Jim"
exactly, had they been cast out of something like A356 then maybe they would of had a better lifespan, I have a couple of 810 cylinders and doubt that I'll bother trying to fix this problem.
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You could use yours as patterns to make new better ones :lol:

Jean
 
well there are enough people making quality ones now, if no one was making them then .........
 
madass140 said:
"I got the feeling they were cast from old Amal carb bodies. Jim"
exactly, had they been cast out of something like A356 then maybe they would of had a better lifespan, I have a couple of 810 cylinders and doubt that I'll bother trying to fix this problem.
Click to expand...

I have to admit that I would probably not have gone so far to try to repair the ones I have, but Piero seemed to really want an original 810 kit to complete his Dunstall project, and I just got caught up in the challenge. When I get the new liners in, I'll renovate the other cylinder I have, and sell it, and that will be the end of my leftover Dunstall bits, and I won't miss them.

Ken
 
I still have two sets of Dunstall barrels yet and I may have a set of pistons. Someday I will patch them up for e-bay.

I still have two Left Coast racing barrels also that need some work. One cracked between the bores. It has been welded but needs liners. I have a pair of cast aluminum liners to fit.

The other got hit really hard from the bottom when a flywheel came apart. It's probably scrap metal. Jim
 
comnoz said:
I still have two sets of Dunstall barrels yet and I may have a set of pistons. Someday I will patch them up for e-bay.

I still have two Left Coast racing barrels also that need some work. One cracked between the bores. It has been welded but needs liners. I have a pair of cast aluminum liners to fit.

The other got hit really hard from the bottom when a flywheel came apart. It's probably scrap metal. Jim
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I'm afraid the warranty has run out on those Left Coast Racing cylinders, Jim :p

Actually, I still have a couple of them around that need repair, and I hope to someday get around to putting them up for sale. Just trying to clean up some of the mess around here (to make room for more junk, of course), but I sometimes feel like Hercules cleaning the Sisyphian stables.

Ken
 
Did Wellworthy Alfin do a cylinder for the Commando ?
 
The only people I know of who had their own castings made for alloy Commando cylinders were Dunstall, D. Robertson, Steve Maney, and Kenny Dreer. There might be others, but I haven't run across them. I know of two people now who have made their own alloy cylinders from billet, Ron Fraturelli back in the '80s, and lately our own comnoz. There are probably others who have done so, but I haven't run across them. It's amazing sometimes what people manage to do in their garages and garden sheds that we never hear about.

Ken
 
lcrken said:
madass140 said:
"I got the feeling they were cast from old Amal carb bodies. Jim"
exactly, had they been cast out of something like A356 then maybe they would of had a better lifespan, I have a couple of 810 cylinders and doubt that I'll bother trying to fix this problem.
Click to expand...

I have to admit that I would probably not have gone so far to try to repair the ones I have, but Piero seemed to really want an original 810 kit to complete his Dunstall project, and I just got caught up in the challenge. When I get the new liners in, I'll renovate the other cylinder I have, and sell it, and that will be the end of my leftover Dunstall bits, and I won't miss them.

Ken
Click to expand...
Hi,
here in Italy we have easily registered again the old untitled and without plaque bike that have more than 25 years.
But the bikes must be completely original in every detail and tax inspectors are very well prepared.
I have a complete 810 Dunstall, I also found the fairing front mount (thank you David for such gift).
So I need the stock cylinders and pistons and thank Ken who has adjusted for me.
I hope that the tourist can use fit!.
Ciao.
Piero
 
Hehehe Piero, so easy titled and registered eh, down to the detailed original, it takes the likes of Ken to satisfy the examiners. How pensive should Piero be once up and running? I've sure dreamed of some way to cable down the head to the cradle but that would not pass inspection.
 
As the owner of an 810 Dunstall I wish I had never seen this thread. My Dunstall cylinders pulled the studs very early in their life which was soon evident with a blown head gasket. After lifting the head I found several of the studs had pulled, and the cylinder liners were about .020” below the surrounding aluminium surface.
All the 3/8” studs were fitted with thread inserts and threaded bushes were made for the 2 front 5/16” studs. The top of the cylinder was surfaced to finish flush with the top of the liners.
The bike has subsequently done over 100,000 miles without any further head stud problems ( and has a higher com than original due to the cylinder shave) but with the talk of old amal carb bodies as the casting material I will now wonder if I will make it home on my next run.
But maybe there is some hope as I have never stripped a screw in an amal carb, so please dont tell me that the aluminium alloy was worse than the mazac of the amal.
ando
 
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