920cc Conversion

trident sam · Nov 16, 2013

I got a set of barrels here that need new liners, so is there much advantage in fitting a 920 kit . I'm not going to strip an otherwise good motor, but I don't mind playing with the carbs etc . Cylinder head is gas flowed all ready, standard peashooters fitted. Where (if at all) will I see a benefit in a road bike ?
sam

Nortiboy · Nov 16, 2013

Lots of work to fit the 920. Opening the crankcase "throats" to take the larger sleeves. You need to clock the head to the barrels. A bit of engineering involved for very limited gain on a road bike. On mine you see the sleeves between the fins. Not a lot of meat to work with. I did it as the amount of damage I had gave me no choice.

I would replace original sleeves. Hope this helps

trident sam · Nov 16, 2013

Thanks a lot for info, I always thought it was a bolt on mod.
Ill just get the barrell re sleeved to standard.
sam

Fast Eddie · Nov 16, 2013

trident sam said:
Thanks a lot for info, I always thought it was a bolt on mod.
Ill just get the barrell re sleeved to standard.
sam

Strewth, you capitulated un sportingly early there Sam!
I thought better of you sir.
FE.

worntorn · Nov 16, 2013

"you can see the sleeves through the fins"
I'm amazed that this holds together. I'm also amazed that anyone sells such a kit.
Further amazed that I bought one! :shock:

On further thought- Roger at RGM recommended fitting the kit only to the 850s, cant remember whether this was because of the strengthened crankcase of the 850 or because of more material in the barrels.
Nortiboy, did your 920 kit go into a 750 or 850?

Glen

comnoz · Nov 16, 2013

I've made quite a few leaky cylinders.

No problems with a nice thick sleeve installed.

They work good up to about 79 or 80mm bore but when you go larger than that they don't like to stay round anymore. The sleeves get pretty thin. Jim

worntorn · Nov 16, 2013

Just doesn't look right somehow, but maybe a bit like sitting in an attic looking at daylight coming thru all over a nice dry shake roof. It looks like it cannot work, but it does!
I believe most or all of the 920s use 81 mm, as my RGM kit does, so this is going to be in the short lived category?

Glen

comnoz · Nov 16, 2013

worntorn said:
Just doesn't look right somehow, but maybe a bit like sitting in an attic looking at daylight coming thru all over a nice dry shake roof. It looks like it cannot work, but it does!
I believe most or all of the 920s use 81 mm, as my RGM kit does, so this is going to be in the short lived category?

Glen

I really only have direct experience with 2 of them- one was my bike. When I first built it I installed a 920 kit but I had oil consumption problems and head gasket problems. I fixed the head gasket several times along with resurfacing everything and tried a couple different types of piston rings but I never did get it to stop using oil. I finally gave up and sleeved it down to an 880 with a 79mm bore and o-rings. I didn't have a dyno at that time but I couldn't feel any loss of power. I used it that way till I blew it this fall.

Of course I was doing long distances on it and 4 or 500 miles to a quart was not acceptable to me.

I built one for another guy a few years back [RGM kit] and o-ringed the cylinders. That seemed to help with the gasket problem but it still used oil. He rode it for a while but I don't know where it ended up. Last time I rode with him it was puffing on every shift. Jim

Nortiboy · Nov 16, 2013

worntorn said:
"you can see the sleeves through the fins"
I'm amazed that this holds together. I'm also amazed that anyone sells such a kit.
Further amazed that I bought one! :shock:

On further thought- Roger at RGM recommended fitting the kit only to the 850s, cant remember whether this was because of the strengthened crankcase of the 850 or because of more material in the barrels.
Nortiboy, did your 920 kit go into a 750 or 850?

Glen

Gooday Glen,

You can see the sleeves in spots, Does not seem to worry it.

It is in an 850 MKII

Cheers

Mark

Nortiboy · Nov 16, 2013

[quote="comnoz

Of course I was doing long distances on it and 4 or 500 miles to a quart was not acceptable to me.

[/quote]

I have not had oil consumption issues (yet). Bit nervous about the unsupported liner at the barrel bolt head counterbores.

Mark

worntorn · Nov 17, 2013

Jim and Mark, thanks for the info. After reading here I think I will leave the kit on the shelf for the time being. The bike runs great now at 828 cc and finally has a good seal on a thin headgasket, no oil showing up anywhere, either leakage or out the exhaust, has tons of power, so I should leave it be.
Might use the kit on a project bike someday.

Glen

trident sam · Nov 17, 2013

Fast Eddie said:
trident sam said:

Thanks a lot for info, I always thought it was a bolt on mod.
Ill just get the barrell re sleeved to standard.
sam

Click to expand...

Strewth, you capitulated un sportingly early there Sam!
I thought better of you sir.
FE.

Hi Nigel.

Fact is , I got a 988 Beadling barrell and Omegas to fit on my orange T160 in the winter, so I don't want to make a bad decision about a 920 on the Commando , if the conversion was just bolt on and with a comparable price as a set of liners I would have been interested. Looking at the most recent posts, it might be just asking for trouble.
Anyway, how's your Commando going ?
sam

Fast Eddie · Nov 17, 2013

trident sam said:
Fast Eddie said:

trident sam said:

Thanks a lot for info, I always thought it was a bolt on mod.
Ill just get the barrell re sleeved to standard.
sam

Click to expand...

Strewth, you capitulated un sportingly early there Sam!
I thought better of you sir.
FE.

Click to expand...

Hi Nigel.

Fact is , I got a 988 Beadling barrell and Omegas to fit on my orange T160 in the winter, so I don't want to make a bad decision about a 920 on the Commando , if the conversion was just bolt on and with a comparable price as a set of liners I would have been interested. Looking at the most recent posts, it might be just asking for trouble.
Anyway, how's your Commando going ?
sam

Ayup Sam,
Well at least you know Beadlings stuff is as good as it gets. Mines got new tyres and RGM disc etc. Omega pistons (approx 9.6:1 - it was actually only 8:1) ready to go in. Cam followers badly scoured though, possibly by blast media? Cam follower tunnels too. Hence one solution is JS lightweight followers and a new cam. Final investigations ongoing...

comnoz · Nov 18, 2013

Here is another 920 kit problem I have seen on barrels that have been sent to me for repair. With the 81mm bore the sleeve is so thin they tend to crack at the base where they are unsupported.

trident sam · Nov 19, 2013

Thanks for posting that Jim.
Definately off my bucket list now.
sam

crusadersports · Nov 19, 2013

comnoz said:
Here is another 920 kit problem I have seen on barrels that have been sent to me for repair. With the 81mm bore the sleeve is so thin they tend to crack at the base where they are unsupported.

with apologies for jumping in on your thread trident sam...

Jim: that begs the question: Is there a good/sound way to convert to 920? Steve Maney does a 920 alloy barrel. I was thinking a set of those with some of jseng 's lightweight pistons & rods should work well?

comnoz · Nov 19, 2013

Without going to a wider bore center as SM does for his 1007 kit, I generally figured 79.5 was about the maximum bore for a long lived Norton. 79 mm is better.

Combine that with a 93mm stroker crank and you can have a very good running 913 or 923cc engine.

Due to the fact that a Norton is breathing limited by the possible valve sizes, you will gain more by going longer on the stroke than you will by increasing the bore. Jim

Fast Eddie · Nov 24, 2013

comnoz said:
Here is another 920 kit problem I have seen on barrels that have been sent to me for repair. With the 81mm bore the sleeve is so thin they tend to crack at the base where they are unsupported.

Hey Jim,
That picture seems to support the argument for using the JS pistons and longer rods wouldn't you say? The longer rods would put the wrist pin over 1/2 inch further up the bore at BDC... And have less angularity... Taking a lot of stress off of the liner skirt.
What is your thinking on this?

comnoz · Nov 24, 2013

[/quote]
Hey Jim,
That picture seems to support the argument for using the JS pistons and longer rods wouldn't you say? The longer rods would put the wrist pin over 1/2 inch further up the bore at BDC... And have less angularity... Taking a lot of stress off of the liner skirt.
What is your thinking on this?[/quote]

I have had thoughts along that same line.
The liner is still so thin with the 920 that bore distortion would be a concern up higher in the barrel. Jim

worntorn · Nov 24, 2013

Roughly how thick is that liner when bored to 81mm?

Glen

920cc Conversion

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