850 mild tuning

I'm thinking of doing some mild tuning to my 850 MkII. The aim is to get a reasonably quick bike that will be used mostly for fun riding on weekends and some track days. I do not want to lose reliability, nor do I want to spend heaps of money at this point (otherwise I would be going the same route as Fast Eddie).

My plan is to strip & inspect the engine this winter. The crank will be stripped, cleaned and balanced. Bearings & pistons to be inspected & replaced if necessary with standard items. A PW3 cam & new followers will probably go in, with the valve timing to be checked.

I will measure the current compression ratio, and plan to adjust to around 9.5:1, either by using Jim Schmidt's ultra thin head gasket or by skimming the head if necessary.

I have a XS reed valve currently fitted, which will probably be mounted direct on the breather outlet from the TS case.

Gearbox to be stripped & checked - I have a oil leak from the joint faces there somewhere.

Current Boyer seems to be dead, so it will probably be replaced with a Pazon Surefire. There's a rod link headsteady fitted.
Other than this, the engine will be standard, running the non-balanced peashooters and some form of foam sock air filter - the carbs currently have trumpets on them.

Alloy rims (WM3 x 19) front & rear, RGM floating disk & AP racing alloy caliper are already fitted together with a set of Landsdowne dampers (thanks John).

Comments anybody? While I would love a set of the JS rods & pistons (plus a raft of other goodies!), that's rather over the current budget. Instead of buying the JS valve train, I would rather get the crank balanced.

/Steve in Copenhagen.

Hey Steve,

Sounds like a prudent upgrade. We've done variations of this several times on customers' bikes and with everything else in concert it is a wonderful upgrade.

With the hotter cam you'll need to open your cam tunnel in the cases, and a portion of the lifter tunnel in the cylinders, for clearance. You will also need to cut reliefs in the piston tops for proper valve clearance, particularly when you're reducing gasket thickness to up compression.

HTH,

-Kenny

Thanks Kenny, that's encouraging. By the way, what's the max. compression that can be used with normal petrol? Here in Denmark, 97 octane is fairly common, equates to 93 octane in the US, but we don't seem to get the exotic chemical blends that you blokes have. Just a bit of bio-ethanol chucked in.

Just wondering what would be good to use together with the PW3 cam - I believe it likes a reasonably high compression ratio?

Is it worthwhile using the Total Seal 2nd rings with the standard pistons? are they available in the correct dimensions or do the ring grooves need to be modified?

Cheers,
Steve.

Steve, I run 10.5:1 in the UK and have had no issues. I was nervous, but thought I'd give it a go and its been fine. I even ran it for a full days track use with the ignition timing retarded a lot (unsure exactly, but around 10 degrees) and even though that really blued the pipes, there were still no knocking / pinging issues. You get good fuel in DK and do not have prolonged super hot summers and million mile long straight freeways, so I would personally be brave with the CR.

This might be linked to the fact that at that CR, with a flat piston, the squish band is functioning well?

Anyhow, with a big cam you will lose some effective CR and thus need to bump it up somehow. If you do not need to renew pistons, you can do this by skimming and JS head gasket rings. If you need new pistons, then I would definitely by new quality high comp pistons. AN sell the Wisco pistons that Hemming used to (still does?) deal in and Maney sells his own pistons. Both very well proven of course.

With a decent cam and a CR hike you'll have 90% of the gains I had for (ahem) a little less outlay.

Consider replacing the cast iron flywheel. It will explode if you take it up to 8000 rpm.

Hope you understand some German:

Broken link removed

Thanks for the comments Eddie. By the way, with the 10.5:1 CR, how the starting? Since you use the bike on the road as well, I presume it's just a bit harder, as opposed to getting a large fat mate to jump on the kickstart from a considerable height?

Regarding the steel flywheel link that Johntickle sent, I' dont know this bloke (http://www.britishclassicbikes.de/) - his web site looks good, any personal experience of his work?
The price for fitting the flywheel & balancing sounds very reasonable, even allowing for p&p to Gerrnany.

SteveBorland said:

Thanks for the comments Eddie. By the way, with the 10.5:1 CR, how the starting? Since you use the bike on the road as well, I presume it's just a bit harder, as opposed to getting a large fat mate to jump on the kickstart from a considerable height?

Regarding the steel flywheel link that Johntickle sent, I' dont know this bloke (Broken link removed) - his web site looks good, any personal exp? the price sounds very reasonable, even allowing for p&p to Gerrnany.

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Steve, the Norton is usually a first kick starter for me, of course, one has to have 'the nack' and I have endless fun inviting the uninitiated to try! It does require a hearty swing, but that big flywheel works wonders when you get it spinning. I use the bike on the road mainly Steve, it only gets a cope of track outings per year.

Steve, as you already know, re CR and big cam, things have to be done as a 'package'.

I once rodea professionally built 850 that had a single Mikuni, standard compression and a PW3 cam...

Not wishing to offend anyone here, but I swear my old Tiger Cub had more poke ... !

You still running the standard flywheel then? Did you get the crank balanced during your build?

SteveBorland said:

You still running the standard flywheel then? Did you get the crank balanced during your build?

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Yes I am using a stock crank, although I had the radius ground into the primary output shaft as advised by JS. I considered the German blokes steel flywheel, but feared lengthy hold ups and or possible damage caused by posting my crank there and back. I asked him if I could just buy a flywheel from him due to the postage issue, and for some reason I couldn't quite grasp, he seemed to find this offensive, which was not intended!

But, I figured that the fact they are considered weak if revved above 8,000 would be of little concern to me as intent was (and is) not to exceed 7,000 (much).

Yes I had the crank dynamically balanced and I think this made a big difference. I reckon the factory pretty much ignored this and relied on the ISOs! Dynamic balancing should be a mandatory part of a rebuild IMHO.

I agree with Fast Eddie and his advice. But I personally would not selected PW3 but asked Jim Comstock (Comnoz) if he could deliver a good cam for street. Perhaps a12.
What head do you have, RH4 or RH10? Jim can achieve good flow and velocity results with RH10.

Kvinnhering said:

I agree with Fast Eddie and his advice. But I personally would not selected PW3 but asked Jim Comstock (Comnoz) if he could deliver a good cam for street. Perhaps a12.
What head do you have, RH4 or RH10? Jim can achieve good flow and velocity results with RH10.

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I've never used a PW3, but like many others, I have high regards for Mr PW and his cam designing abilities. Plus there are many who use them and swear by them. In fact I rather suspect we'll be hearing from a few now you have provoked them...!

Fast Eddie, why were you running 10' retarded?

I am about to pull my 850 apart and replace the cam with a 2S combat cam. I've been measuring the lift on the 2S and a standard 850 cam and the 2s seems to have 2.4 mm more height . Am I likely to have things bottoming out ? I really don't want to end up opening-out the tunnel in the crank-cases. That actually means, the motor has to be totally stripped and cleaned out.
Fitting the PW3 cam to a standard motor is probably a good idea. However it can cause the creation of a 'cam spot', revs at below which there is not much power, then when the cam starts to work you get heaps. A lot depends on how you have the exhaust system set up. If it is restrictive, the cam may not give much benefit.
I don't know much about tuning commandos on petrol. I don't think I would raise the comp. ratio. A good cam is the biggest improvement you can make to an old style British bike. When I was a kid we fitted the best available cams to a 1963 Bonneville ( the E3134 exhaust cam has a different number because of the extension for the points), a set of the 1958 BSA Gold Star race cams to a 1955 B33, and a set of rare Matchless competition cams to a mid 50s Matchless. We did not change anything else. The Bonneville was the fastest bike in the local chapter of The Angels. The B33 was excellent. And the Matchless immediately broke a crank-pin.

When we fitted the race cam on the exhaust of the 1963 Bonneville we got more gain than I would have expected. In those days it was not easy to get much info on what was available in the UK, and it meant writing letters backwards and forwards. In Triumph twins there have been a few different race cams used over the years and one of my friends has tried several. He has returned to the E3134 cams - his bike is set up to develop more torque than top end and it is very fast. I once rode it and blew off a good H2 Kawasaki two stroke in acceleration.

brxpb said:

Fast Eddie, why were you running 10' retarded?

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It wasn't particularly scientific...

I had the timing cover off for another reason before hand, in a rush etc, and f*cked up the re-assembly... But don't tell anyone...

Fast Eddie said:

brxpb said:

Fast Eddie, why were you running 10' retarded?

Click to expand...

It wasn't particularly scientific...

I had the timing cover off for another reason before hand, in a rush etc, and f*cked up the re-assembly... But don't tell anyone...

Click to expand...

Aww, thought we'd just uncovered some little known tuning secret. never mind, I've done worse!

brxpb said:

Fast Eddie said:

brxpb said:

Fast Eddie, why were you running 10' retarded?

Click to expand...

It wasn't particularly scientific...

I had the timing cover off for another reason before hand, in a rush etc, and f*cked up the re-assembly... But don't tell anyone...

Click to expand...

Aww, thought we'd just uncovered some little known tuning secret. never mind, I've done worse!

Click to expand...

Quite the opposite. The 10 degrees out is only an estimate. I only found out cos I put it on the Dyno to test different exhausts and discovered I was almost exactly 10bhp down on prior baseline figure!

Brain automatically assumes the worst and I started assume duff cams etc. but it was the ign timing!

I don't ride it frequent enough and I had been playing around with carb settings and exhausts in between riding it, hence hadn't noticed the loss in power, which I should have to be frank cos it was big.

The interesting thing is it still started first kick, ticked over nice, etc. I think it is a testament to the Tri-spark / crane coil combo and FCRs (all from Matt) that the bike continued to run so well. So well in fact, the issue was disguised !

That's also my problem. I built the Seeley in the 70s when I was better in the head. Now I'm a bumbling old fool and anything is likely to happen. The last time I took the bike to Winton, everything went wrong - even down to leaving the clip loose on the return oil line. The worst thing is that due to lack of exercise, I am becoming weaker as I get older. I can still ride the bike, however by the time I've loaded the trailer, I am buggered. The important thing is that I still have the interest and the urge.

You might not have noticed a drop in top end because the bike might have become easier to ride.