Is a 920 kit worth it?

Hello Chaps,

Anyone fitted a 920 kit for road use? Are they worth it in the real world? And does 61bhp sound realistic (RGM figure)? I realise machining of the cylinder mouths in the crank case is nec, attn to ports, cam and carbs to 'release' its potential, so it ain't a simple bolt on job. I have been enjoying my mk3 850 for several years but would like to make it more so ( and see off afew more HDs!!)

crusadersports said:

Hello Chaps,

Anyone fitted a 920 kit for road use? Are they worth it in the real world? And does 61bhp sound realistic (RGM figure)? I realise machining of the cylinder mouths in the crank case is nec, attn to ports, cam and carbs to 'release' its potential, so it ain't a simple bolt on job. I have been enjoying my mk3 850 for several years but would like to make it more so ( and see off afew more HDs!!)

Click to expand...

It's worth it for you to buy it and let us know how it goes. :mrgreen:

Thank you swooshy, continued proof yellow is brighter :mrgreen:

I don't know about the big bore kits for the Norton, but.... I installed a 750 big bore kit on my XS650 a few years ago. Re jetted the carbs, some light port work and a MAC 2-1 exhaust. I don't have any dyno numbers for it but the seat of the pants dyno showes a marked improvment. It's a blast to rip areound on, a bit obnoxious at times. But to wake up a 35+ year old bike definatly worth it.

Thanks Bwolfie,

In 2005 I had a very worn XS650, bought for afew ale tokens. I think the last nodel with twin disks. It was a great Japanese Triumph- it ticked over like a clock.

But once under weigh it handled alarmingly and the old school friend I sold it to delighted in informing me in his official capacity as a member of HM Constabulary that the play in the swinging arm meant it couldn't pass an MOT. I thought of it as a torquey 250. I must admit I did chuckle when he also informed me it leaked oil all over his new garage floor....Proper bike is that, aye lad, they don't make 'em like they used to! :mrgreen:

I don't know if the increase in cc's is "worth" the cost.

But, if you have a stock Mark3, I think you would be very pleased if you did three things

install a new cam with a little higher lift and duration (Megacycle 5600 with mated ground lifters), while you are in there raise the compression a bit, and install a pair of Jim Schmidt's new 32mm flat slides (JSmotorsport.com)

with head off, great time to freshen it up with new guides, valves, clean things up

All this would be quite manageable, and a lot less money than buying the new barrels and pistons, etc, and would end up giving you a very significant performance increase over what you have now, presumably stock

crusader, you'll inwardly already know if your likely to do it! If you're addicted to "improving" your bike like me, you will have to do it just to see if you're delighted or disappointed.......that's my opinion.

I'm on my second 920 at the moment.

The first was a bought from "Fair Spares," now Norvil in the mid to late 1980's. I had one problem with that kit, the liner moved slightly and needed repositioning. It was run with a 4S cam, otherwise standard. There was a definate improvement in torque, but the top end was much the same.

Three years ago, I contacted Roger at RGM, and I was all set to go ahead with the purchase of one of his 920 kits having spoken to the local engineers who were happy to press the liners in for me, and Roger talked me out of it saying that a well tuned 850 was a better option. So I left mine as an 850 at that time.

Last Winter, I bought some 920 barrels and pistons from Steve Maney, to go with my stage 2 Maney cylinder head and PW3 cam. The motor was much crisper, but the compression ratio had gone from about 7.9:1 as an 850 to 9.8:1 as a 920 and so you would expect that to be the case. There was a nice improvement in power and I got better fuel consumption, averaging 60 mpg (imperial gal).

Later this year I put a 2-1-2 exhaust on which lost some of the low reving torque, and moved the power up the rev range a bit, which in some ways is the wrong way to go for a road bike, but once the engine hits 4,500 rpm with this exhaust it really pulls nicely. It goes straight past 100 mph like it used to go past 70 as an 850.

Is it worth it? Well if it's just the power that you're after, going the route I've gone (Steve Maney) was very expensive, but I get as much pleasure in planning and building the engine as I do riding the bike and wanted to get good quality parts. I'm quite confident that there's a bit more power to come out of it. I was going to take it to a dyno this back end and try and optimise the fueling and try both standard and 2-1-2 exausts to see what the differences are, but ran out of time....this'll have to be next year now as I've SORN'd it (taken it off the road).

In September I went to the Classic bike guide, bike breakfast at Markham Moor, and they were doing free runs on the dyno (without exhaust analysis) and I got them to run mty Norton, and it apparently peaked at 61 rear wheel BHP at 6,000 rpm, which I thought was a bit disappionting. Looking at the exhaust fumes, as I was a spectator, it looked a bit rich as there was some "dark" puffs coming out of the exausts, so I will see if it is running rich next year.

With regard to machining the cylinder mouths in the crankcases, I did this myself by hand with some proper scraping tools, a small flap wheel and using engineers blue. But as I said earlier I enjoy doing things like this. So that's my experience. Hope it is helpful.

Is there much extra effort or even risk to kick start these 920's?

I've run several 920 engines in both street bikes and race bikes, and you will definitely notice the difference, particularly in mid-range power. To get full benefit of the conversion, you must hone the cylinders with bore plates, or you will get poor ring seal at the top of the bore adjacent to the through bolt counterbores. It will still feel noticeably stronger in normal riding, but won't make as much top end power. To get significantly more top end power, you'll also have to address cam and head work, and maybe bigger carbs. The stock exhaust works surpbisingly well, as long as you have the peashooter mufflers without the mutes. If you keep the compression ratio reasonable for the street, they are not too difficult to kick start. On a race bike with 11 to 1 CR, they can be very frustrating to kick start. I ended up using an external starter engaging a nut on the end of the crank to start mine after missing several race starts because I couldn't start the bike.

Ken

The 850 Norton Commando was such a mildly tuned engine as it came off the dealer's floor. There are a lot of little and inexpensive things you can do to it that will make it run better than a stocker.

The stock cams were sometimes soft and wore down with use, and that would detune the bike even more as the miles stacked up.

If your cam is not worn down, I wonder if you might just be happy milling the head enough to get it up to 9.5-1 compression along with an ignition-timing adjustment. Would that mod plus a street performance cam give it Combat-like power? It should be close and it would be cheap and reliable.

I don't know how much the pistons weigh in the current 920 kits, maybe they have light ones that do not require rebalancing? I think the older kits were recommended to go with stronger than stock connecting rods.

If money is no object good for you, it is for me though so I always look into the cheap way to get things done.....my habit.

The wish to compete with Harley Davidsons is interesting. They are a mildly tuned twin also, but one that is a lot cheaper to get power out of and more durable also. I have had use of an 1100cc aluminum Sportster this year and have looked into what is available for them performance-wise. I talked to a well-known builder of Harley engines in New England. He said with a $200 set of Wiseco pistons, a set of "red-shift" cams that can be installed without splitting the cases, no re-balancing and some head work any Evolution Sportster can be tuned to put out an easy 100hp. Wow.

They have roller cams, and there have been so many of them made over the last 25 years that it is very easy and very cheap to find good used performance parts for them on Ebay etc.. I would bet someone who is savvy and mechanically inclined could put together that 100hp Sportster upgrade for $500 or less.

I think the stock 1100 and 1200 Sportsters are factory rated around 60bhp and they are really mildly tuned torquers, I hardly ever use more than 1/4 throttle while riding mine in traffic and have it in high gear by 30mph.

I rode a stock 850 Commando for quite a few years and remember it's strong and weak points well on the street and at the drag strip. It was a good all around standard motorcycle which I am sure had a bit more that it could practically give with a minimum outlay, but it seems like when it is tweaked hard the positive returns stack up much more slowly than could be worth it for many people when the cost and reliability is looked at.....

Thanks for the useless post on HDs.
The book on how to get a Sportster reliably to 100bhp is 100+ pages thick.
Now, back to Nortons.

What aircleaner setup do you have on your Norton. ?
Just changing that to the wiremesh and paper filter like Mk1 and Mk2, and tweety mufflers should about see off most HDs.

Crap not only are Hardley Ablesons our closest American cousins now you tell us they make economic sense too. ugh. Thank goodness they ain't known for their success on loose stuff. Ugh. What it they ever rubber mounted them with links. I might jump ship that comes with compression releases, to ease its thumb commencer : (

920 Maney and others that cost like most a whole Sportster can pull about a ton of hp. Then there's that Noevil 1004cc long strok grunter.

Sounds like 850 in Combat spec might be best bang for the bux. Get Jim Schimdt's booklet on Norton Racer mods as best DIY guide to get go.
http://victorylibrary.com/NOR.htm

They rubber mounted some of them, without links.
Using the Norton patent too, or something along those lines.

You gunna jump ship now ?!

P.S. Some of them have a pretty good record on the 'loose stuff.'
If you get one of those steel shoes and learn to get it down, you could impress the neighbours no end...

I don't know about me being able to man handle a Harley like they seem to need to behave on edge. I've run with 1%'rs and the locals so have hi regards on what they can do routinely a Combat is hard pressed to hang with below the ton and left behind in the long runs. The main advantage to sprint with the HD's is a Commando's lightness - which costs about as much to add as hp. i may be a black sheep in some circles but I got these Evel Knivel beasts in Peels 920 sights and hope to tease with current issue Buells too.

Combat 750's make say 49 hp and 920 is ~20% bigger so that implies 9.8 more hp, while prior reports say they get a bit more like 11-12 hp. Gear up enough to make 2nd good to about the ton and you'll likely be happy with the 920 passing grunt and scary top speed. When I read of more power desires I wonder what for and if they know/desire the tire skipping out antics when nailing it leaned.

Maybe what you need Steve is one of these rice burner parallel twin dirt bikes.
http://pictures.topspeed.com/IMG/crop/2 ... 800x0w.jpg
110 hp new out of the showroom, with warranty, claimed 140 mph.
Like you see on the Paris Dakar -rocketing through the desert and the copters can't keep up.

Meanwhile, back to 920 Commandos...

Ugh, I don't put anything on the ground until already crashing, flat tracking style is about total TABOO to me on THE Gravel. Its too too easy to get crossed up sliding wide and just no room or reserves for that luxury. To ride with much spirit takes brute jerky ballistically directed power thrusts BLAP right now digital traction let goes and grabs that only torque punch can do, not lazy dazy hp that depends on rpm climbing delay then over shoot. There is magic when the motor so controls the tire you can set throttle to set tire spin instantly then wait for bike and its reactions to kick in. Set tire spin just so, not more not less or SPLAT, something that's very hard for rpm type hp to do, as delays slightly or over shoots tire spin so takes digital brains to protect pilot. So another thing that binds American and Brit Iron - the real ones ain't got no fly by wire gizmo's. Some day there will be robotic bikes like camel jockies, any one else made plans on how to tackle them?

Another thing with the extra torque may be unexpected wheelies. I want to do this on a Commando, don't you?


[video]http://www.youtube.com/watch?v=FgPPLzK2GiY&feature=related[/video]

Aah! I was not entirely serious about seeing off HDs.

Thanks chaps, especially 1up3down, beng and Reggie for your thoughts on tuning the mk3. It's great to hear about specific mods that can give the mk3 abit more waft- thank you- Very valuable information one could not buy!

Reggie, it must have been your photo in the current CBG that gave me the idea! Small world (and even smaller with this great forum!). Smashing, thanks so much for the advice. I too contacted RGM about their 920 kit and was talked out of it when Roger said a good 850 is almost as good on the road. What a selfless gent he is! But I have since reasoned that with a Mikuni VM34 I am sacraficing even more of the already limited MK3 bhp.

Can I ask what carbs are you running? Even if 61 bhp as a back wheel figure is disappointing to you, it must make for a very exciting Cdo and I would take it any day- compared to what other threads inform me must be about 35-38 bhp for my Mikuni equipped mk3. I once borrowed the (then) girlfriend's restricted (33bhp) GPZ 500 for the 60 mile run to work for a few weeks. I was somewhat underwhelmed to conclude it did everything my MK3 did- with alot less effort- the performance was very similar :shock:

Can I ask roughly what sort of outlay you would deem nec to convert an otherwise reasonably sound mk3? Your initial comment struck a chord- it is at least partly becuase the mk3 is sometimes the butt of electric leg/the start of the rot type comments that I would like to build an indecently rapid example of the genre....

crusadersports wrote;

Can I ask what carbs are you running?

Click to expand...

Amal Mk2 34mm x 2.

crusadersports wrote;

it must make for a very exciting Cdo

Click to expand...

It's a big improvement over last year when it was an 840 (I think as it was +0.040). It had a PW3 and the big valve head and I checked the compression ratio just before I dismantled it, and it was about 7.9:1 I think. Yes I know that I should have done this as I was building it, but I needed it on the road quickly at the time and was impatient. The low compression ratio was due to having valve recesses put in the pistons and the valves in the big valve head are more recessed I believe, taking it down from the typical 8.5:1.

I think it was probably in quite a poor state of tune overall then (in that particular spec), a bit mismatched, as it was quite pedestrian passing traffic on the open road and got to about 90 reasonably OK, and then crept up to 100.

Now, it sounds crisp and it quite brisk (for its age group) passing other traffic and I rarely consider knocking it down a gear just twist the throttle back and she's off(I usually ride two up with a combined weigt of 20 stone), and so in that respect I'm quite pleased, and as I said 90 to 100mph it is pulling nicely and takes only a few seconds and I don't usually push it much over 100. If my shite memoty serves me well, it was topping out at about 110/115mph

As Icrken said (I think) and as it was with my former 920 (and another one I built for a friend), with just the capacity increase you will get more torque which is quite satisfying, but the top end may be similar to what it is now. Obviously there are lots of variables such as cam type and compression ratio which will have some effect on what the outcome is.

Steve Maney is very helpful, and advised me that if I wanted it to breath properly that a large valve head was needed, but maybe on a road bike this is not necessary as it is more the midrange that is important? I have paid attention to getting the squish band gap and compression ratio correct when building this 920, but as I said I'm sure that with a bit of tinkering with cam timing, carb jetting and exhausts that there is some more potential....we will see.

I would say if you wanted to convert a relatively standard OK Commando, the barrels and pistons alone would give you the biggest gain with a non standard cam. The RGM kit done properly will probably be quite OK. I don't know if Norvil still do them? But personally wouldn't be in a hurry to deal with them. I went with Steve Maney as you know that you are very unlikely to have problems with quality and this has proved to be the case.

I aslo have on mine,
a stage 2 head,
34mm X2 Amals
34mm inlet manifolds
an optional 2-1-2 exhaust.

By getting the cam and the head done the year before, I spread the cost over two years.

Sorry if I'm rambling but I've done a 12 hour shift today and need to go to bed now before tomorrows slog. I hope it makes some sort of sense?

P.S. I'm not in the photo in CBG. That's my son and my wife. I was stood behind Nigel Clarke as I'm camera shy

Hi Reggie,

Thanks for your post and all the details- that's really helpful! I guess it's easy to get carried away, but it sounds like just fitting the 920 barrels and pistons and may be carbs to suit would suit my purposes well enough. Then a stage 2 could be a new cam and a bit of work on the head/ports.

Dare I ask what the Steve Maney barrels and pistons cost?

I do like the mk3 just the way it is but a bit more bhp would be nice. I never realised when setting up the Mikuni, that it was a trade off- a gain in clean running for a loss in bhp. How do you find the mk2 Amals in terms of clean running/frequency of balancing/reliable tick over? I was impressed that your mpg increased! I used to get 33mpg on worn MK1 Amals and now get 55-60mpg on the Mikuni.

Don't be camera shy mate- you've got such a great bike, why not bask in it a wee bit?? Especially after a 12 hr shift- (but got to fund that Norton somehow!)Anyway, thanks again- more power to the white rose! :mrgreen:

http://www.stevemaney.com/index.html

Steve Maney Parts.

While you're at it man up and spring for the 1007CC kit.