Author Topic: Gear driven primary on a 750? (Read 9836 times)

lordmoonpie · « **on:** October 20, 2009, 02:11:02 am »

There's lots of debate and theory and even a bit of practice around primary drive chains for racing and high speed riding on the 750 using the original dual chains but uprating them, changing to a 750A crank and a GL1000 cush drive with hy-vo chain etc.

While I was packing up a load of old bike magazines to send off to the troops in Afghanistan I ended up flicking through a few of them and there was mention of converting a 750 to a gear driven primary drive, I suppose something like on the 350 K4 twins. It would obviously solve the chain drive problems for a tuned engine but how much work would it be and would it even be possible?

Any engine gurus want to cast in their thoughts....?

mec · « **Reply #1 on:** October 20, 2009, 02:57:20 am »

my thoughts:
my 1000ccm engine with stock 2 roller chains delivering 113 rear wheel HP runs flawless (under racing conditions) this year doing 13 or more practice sessions. this was not what i was exspecting, but what i was hoping. one time in my 140hp 4valve dohc 1130ccm bol d´or i broke a brand new hi-vo chain. therefore i fear that my 1000ccm engine will brake the two roller chains as well........but nope; till now.
if you are running an engine with similar or even less power there is no need for another primary drive (exept for noise reduction).

is the conversion doable?
everything is doable, but: you need a new crankshaft with incorporated primary gear (expensive and doable). to have the proper rotating direction you have to add another "secondary primary shaft" with bearings. where are these bearings located in the cases? are the cases stiff enough in this area? you would have to "redesign" the cases in some way. this "improvement" adds considerable weight to a heavy engine and increases inner friction of the rotating gears.
better way is to relocate the complete transmission an to go without the sprocket shaft........new cases anyway.

interesting technical challenge, but no good cost/performance ratio.

mec

voxonda · « **Reply #2 on:** October 20, 2009, 03:11:14 am »

Look at the first RCB endurance racers, they had what we want(?). Necessary? No, absolutely not. Nice to have? Yes,

Imho the stories about the primary chain are getting out of hand the longer the saga goes. I am with Mec, everything is doable, at a cost. But if his 'monster' can't destroy the chains what will. I go for the reinforced once, because I have to replace. The oem set that I have will be used in another engine.

Rob

MRieck · « **Reply #3 on:** October 20, 2009, 05:04:32 am »

Just run a set of the heavy duty primary chains Nippon/Ricky Racer are selling. They have quite a few sets that I'm sure they would be willing to sell to folks on the board.

bert96 · « **Reply #4 on:** October 20, 2009, 01:15:05 pm »

Is it really more quiet with these chains?

Bert

Ricky_Racer · « **Reply #5 on:** October 20, 2009, 02:11:28 pm »

Since you asked... Bert, since the CCC Superduty Primary Chains have shown approximately 20% of the stretch of OEM primary chains at a field tested 60,000 miles, yes, they will be quieter. But perhaps the most important thing about them is that they will save costs by eliminating the need for repeatedly splitting the case multiple times a season for the repeated replacement of OEM primary chains. And, of course, their increased strength will hopefully reduce DNF's due to failure of the OEM primary chains when used under extreme conditions. RR

Bill/BentON Racing · « **Reply #6 on:** October 20, 2009, 04:58:16 pm »

RR,I need a set for 1000cc build.PM please,Thanks,Bill

JLeather · « **Reply #7 on:** October 20, 2009, 05:32:21 pm »

Ted, we'll see what those chains can take. I'm putting a set in my turbo motor. Now, I won't be downshifting at 11k like mec, but I'll be hammering it at the strip once in a while. I expect something else to fail first, having seen and heard what these chains can do.

Sam Green Racing · « **Reply #8 on:** October 20, 2009, 05:41:25 pm »

Ya need a nice auto trans to take out the snatch

Have you still binned the auto idea?

Sam.

Ricky_Racer · « **Reply #9 on:** October 20, 2009, 07:27:24 pm »

Quote from: bellcow54 on October 20, 2009, 04:58:16 pm

RR,I need a set for 1000cc build.PM please,Thanks,Bill

PM sent as per your request. Thanks, Bill! RR

nippon · « **Reply #10 on:** October 20, 2009, 11:17:36 pm »

Hi,
a new 15 pages chain catalog is ready to download.
http://www.classiccyclecity.com/gallery/displayimage.php?album=48&pos=13

A short description:

With brand new stock RK primary chains, the lower crank case to chain tensioner
sag is 65.00 mm. In a stock engine (around 50 hp
at the rear wheel), stretch after 2-3 races results in 67.00-68.00 mm
sag. In a tuned race SOHC engine (100 hp at the rear wheel), we
measured a 71.00 mm! sag after three races.
Replacement of the primary chains is highly recommended by Honda at
70.00 mm sag in order to avoid engine damages. Since our test results
confirm a rather short life for the stock primary chains.
With our brand new heavy duty primary chains, the lower crankcase
to chain tensioner sag is 63.70 mm, so our high performance primary
chains stretched only 1.30 mm to 65.00 sag after three races in
a 91.2 hp SOHC engine, we did not reach the sag limit. Neither did we,
in road tests of over 60.000 miles with stock engines, reach the specified
sag limit. We highly recommend the use of our chains in stock engines,
too. The limited stretch of the chain will reduce the primary chain rattle.

nippon

MRieck · « **Reply #11 on:** October 21, 2009, 04:44:15 am »

Quote from: nippon on October 20, 2009, 11:17:36 pm

Hi,
a new 15 pages chain catalog is ready to download.
http://www.classiccyclecity.com/gallery/displayimage.php?album=48&pos=13

A short description:

With brand new stock RK primary chains, the lower crank case to chain tensioner
sag is 65.00 mm. In a stock engine (around 50 hp
at the rear wheel), stretch after 2-3 races results in 67.00-68.00 mm
sag. In a tuned race SOHC engine (100 hp at the rear wheel), we
measured a 71.00 mm! sag after three races.
Replacement of the primary chains is highly recommended by Honda at
70.00 mm sag in order to avoid engine damages. Since our test results
confirm a rather short life for the stock primary chains.
With our brand new heavy duty primary chains, the lower crankcase
to chain tensioner sag is 63.70 mm, so our high performance primary
chains stretched only 1.30 mm to 65.00 sag after three races in
a 91.2 hp SOHC engine, we did not reach the sag limit. Neither did we,
in road tests of over 60.000 miles with stock engines, reach the specified
sag limit. We highly recommend the use of our chains in stock engines,
too. The limited stretch of the chain will reduce the primary chain rattle.

nippon

You really have to see these chains in person and compare them to OEM to appreciate them. Well thought out and well executed.

simon#42 · « **Reply #12 on:** October 21, 2009, 09:49:55 am »

hi rr i would like a set of there as well , could you p.m. with price please

Ricky_Racer · « **Reply #13 on:** October 21, 2009, 11:55:43 am »

Thanks, Simon. PM sent. RR

JLeather · « **Reply #14 on:** October 21, 2009, 12:06:11 pm »

Sam, the auto idea got binned when I opened up the bottom end and found it was trashed. After pricing clutch packs and other 'matic parts I decided they're just too expensive to rebuild, and I don't like the idea of putting this much money into an engine that I can't rebuild if I break it.

simon#42 · « **Reply #15 on:** October 22, 2009, 10:09:57 am »

Quote from: Ricky_Racer on October 21, 2009, 11:55:43 am

Thanks, Simon. PM sent. RR

thanks ted , as you said it looks like a must have mod !

kos · « **Reply #16 on:** October 22, 2009, 12:17:18 pm »

Those new HD chains are on e-bay right now $395.00 buy now price.

KOS

kos · « **Reply #17 on:** October 26, 2009, 08:49:03 pm »

Yes, as someone said early on on this thread....anything can be done, if you want it bad enough. Try this on for size. The only part that will be hard is the gear that you must put on the crank to drive the driven sprocket/gear on the mainshaft of tranny.

We'll, let s start making new cranks. I'll get right on it.

How many does anyone want?

KOS

Sam Green Racing · « **Reply #18 on:** October 26, 2009, 09:05:41 pm »

and at only $15,000.00 that's gotta be a good buy.

Sam.

KRONUS0100 · « **Reply #19 on:** October 29, 2009, 01:06:12 pm »

somewhere i actually have a pic of the factory gear driven primary on the early race cb750 bikes....see if i can find it

KRONUS0100 · « **Reply #20 on:** October 29, 2009, 01:08:14 pm »

ok i found it...holding it up for you all to see.....how do i get it on my computer and posted here? i believe i still have a photobucket account.............

KRONUS0100 · « **Reply #21 on:** October 29, 2009, 01:38:26 pm »

ok....not sure how to...this image is at image shack under mbrizfam590.....anyone care to try and upload it here go ahead.

Sam Green Racing · « **Reply #22 on:** October 29, 2009, 02:48:56 pm »

Where are all the IT boffins when you need them.

Sam.

voxonda · « **Reply #23 on:** October 29, 2009, 02:56:34 pm »

Think you mean this one:

It's the first 1976 RCB with the engine strongly resembles our engine.

Rob

nippon · « **Reply #24 on:** October 29, 2009, 04:36:47 pm »

I guess it was done by Eckert, right?

News:

Author Topic: Gear driven primary on a 750? (Read 9836 times)