Sage advice needed for an 850 MK3 ES rebuild

Hello all,

I am in the process of rebuilding my mk3 850 ES on the "broke college student" budget, but have quite a few questions.

I am placing all the questions here to try and make things easier, but can break things up if need be/ mods require it.

Background:
This was my high school ride and first street bike. Rode for a few years on it when the transmission output shaft seal failed. As I started to dig into it I found i was in bigger trouble than I had originally thought. The primary chain sprocket fell into my hands after I pulled the nut off, the cam had a flat intake lobe [3s cam], gearbox needs a rebuild, the crank was trashed, and the head was not looking to good. Thus I have had to perform a full engine and gear box rebuild. Unfortunately this happened while I was in college and I just now have the ability to start getting it rebuilt.

The bike:
My bike is a 75 850 MK3 ES.
SN: 330xxx

Expected use of the bike: Spirited riding in the canyons. This will be my only street bike for a while so it will be ridden almost every day. I would like to build this to be a reliable motor that has been massaged over just a little.

Current machine work/parts:

RH4 head rebuild w/ new valves and hardened seats.
This has also had .045 milled off for a 1 pt. compression increase.
The pistons have also been notched for valve clearance.
New to me crank. This will have to go out for balance.
+.020 oversize on the barrels.
These measured good, just had them honed/deglazed.
The pistons look to be stock oversize units, and will be retained. No cracks/nicks were found.
The rods are stock. No nicks were found, and will be reused.
Originally the bike had Amals on it and those will be re-used for now.I would like to go to twin mikunies or flat slides/smoothbores but will have to wait to see how my funds are doing after the bike is back on the road.
Boyer ignition.
Cam: This will be a #12 webcam grind.


So here is where I will need the advice of people who have been through this dance a few times, and can point out things I haven't noticed before.
Feel free so send me to a different thread, but I have been researching the threads here to try and answer some questions.


Since I have to replace the primary drive I have been looking into the belt drives. I have found quite a bit, but there is a lot that seems missing.

My questions here are:
- What is the average life expectancy/ service interval that can be expected? I will be retaining the ES functionality.
- For those who have had a belt drive for a while would you do it again?


I have also looked at the QPD quiet drive/ norvil/ maney / RGM kits. I gather from the forums that the Maney seems to be the best save for sprocket tooth selection, which is the strength of the norvil unit. Can anyone who has run either of these units also chime in on these?

I know the chain is a bit more forgiving. While it would be nice to get rid of the oil, the belt sounds like it would be more maint. intensive as some bearings in the ES system would need to be packed with grease every 1000 or so miles. I only saw one small thread about belt maint. so any help here would be appreciated.

The belt would be run in an enclosed [non vented] primary as CO is not forgiving weather wise.

Currently I am leaning towards going back to the chain as it seems that with a properly sealed primary it will be less maint. and will last longer. I though have not heard from someone who has had a belt for quite a while and who would be putting over 10,000 mi a year on a bike. [the last few years I have averaged 15,000 a year on a bike.]


Lifters:
I have seen the stuff that Jim at JS motorsports sells. I have a few questions here.
http://www.jsmotorsport.com/products.asp
I will be using the stock push rods, and i do believe the webcam is designed with the flat follower profile. Would these be a worth while upgrade?
Has anyone had any issues with longevity with these parts?

Thanks again!

nortonmachineshop.com

Give me a call. Jim 719-646-2610

Search all of here & www plus talk to vendors world wide - especially about sprag device, for rational decision =>
part it out now while still a market and word gets out - there are other Commandos, not so commonly known, because not so routinely in the subject line. Anything else to me would seem pure emotional challenge based or no other option desperate but hey they clean up nice as any other Commando and invite a supportive social life.

comnoz said:

nortonmachineshop.com

Give me a call. Jim 719-646-2610

Click to expand...

listen to The Man.

Stick with the chain primary drive if you want to retain the electric start. IF you really want to use a belt drive and still have the electric boot you will have to use an oil proof belt and run it in oil. The electric start mechanism requires lubrication otherwise it will destroy itself. No one makes decent triplex chain anymore, If you need a new primary chain of bulletproof quality you will need a Iwis Duplex chain from the Chainman (I use one on my Mk3)
Engine wise, unless you treat the whole package as one (by that I mean from the carb inlet to the end of the exhaust) just replacing the cam and one or two other bits does not give the huge jump in power people expect to see. Mr Comnoz will advise as it will all depend on how deep your pockets are.
regards
Peter

The #12 grind cam is not a racy cam. It is a cam that is a small improvement in drivability over a stock cam.

It has slightly higher lift for a small increase in midrange torque. It also has a few more degrees of lobe separation [less overlap] which tends to broaden the powerband and make the motor less fussy.

It is a very good replacement cam for a basically stock motor. It is the cam that is in most of the CNW bikes. Jim

Don't forget to replace the tranny layshaft bearing. Known to be bad and a failure will put you down on the road. Search "layshaft bearing" for days of reading.
Jaydee

dobba99 said:

Stick with the chain primary drive if you want to retain the electric start. IF you really want to use a belt drive and still have the electric boot you will have to use an oil proof belt and run it in oil. The electric start mechanism requires lubrication otherwise it will destroy itself. No one makes decent triplex chain anymore, If you need a new primary chain of bulletproof quality you will need a Iwis Duplex chain from the Chainman (I use one on my Mk3)
Engine wise, unless you treat the whole package as one (by that I mean from the carb inlet to the end of the exhaust) just replacing the cam and one or two other bits does not give the huge jump in power people expect to see. Mr Comnoz will advise as it will all depend on how deep your pockets are.
regards
Peter

Click to expand...

+1

Thanks for the advice all.

dobba99 said:

Stick with the chain primary drive if you want to retain the electric start. IF you really want to use a belt drive and still have the electric boot you will have to use an oil proof belt and run it in oil. The electric start mechanism requires lubrication otherwise it will destroy itself. No one makes decent triplex chain anymore, If you need a new primary chain of bulletproof quality you will need a Iwis Duplex chain from the Chainman (I use one on my Mk3)
Engine wise, unless you treat the whole package as one (by that I mean from the carb inlet to the end of the exhaust) just replacing the cam and one or two other bits does not give the huge jump in power people expect to see. Mr Comnoz will advise as it will all depend on how deep your pockets are.
regards
Peter

Click to expand...

Dobba99/Peter thanks for the lead on the Iwis primary chain. Since I will be going the chain primary route I will look them up.
Engine wise all I have done at the moment is to attempt an oil tight engine and slightly warm it up a bit. Being at over a mile high in elevation means that most bikes feel a bit off/ down in power. The midrange grunt that the #12 grind webcam and the compression increase should help the bikes tractability around town/canyons.

jaydee75 said:

Don't forget to replace the tranny layshaft bearing. Known to be bad and a failure will put you down on the road. Search "layshaft bearing" for days of reading.
Jaydee

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Jaydee I will look that up as I was not aware of any big failures coming out of the transmission. Originally since the kickstart started to move under WOT accelerations I was going to order the full rebuild kit from Norvil. After finding out how bad things really were in the engine, it just makes sense to hit the gearbox as well.

Hobot thanks for pointing out the sprag device. When I got the bike the ES setup had been removed and was in a box. This will be my first time going through the ES side of it.

Thanks again for everyone's input.
Eric.

The factory layshaft bearing was made in Portugal. There is a Timken replacement, but I don't have the part #. If you take the old Mickey Mouse bearing to a good bearing supplier, they can match it for you.

Danno said:

The factory layshaft bearing was made in Portugal. There is a Timken replacement, but I don't have the part #. If you take the old Mickey Mouse bearing to a good bearing supplier, they can match it for you.

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Discussed several times before, but the recommended replacement for the standard 6203 ball bearing is the NJ203E roller bearing or the FAG 6203TB P63 ball bearing.