Topic: CB750 AHRMA Sportsman 750 Racer

[slikwilli420]

Got the cases split today and pulled the crank, marked the bearing halves, pulled the rods and started cleaning.

Going to build a box to ship the crank and Cycle X rods off to Cycle X for lightening, balancing and rod install this week.

Regarding bearings, does everyone generally replace all of them? Is there a source for a whole set? CMSNL has them piecemeal but was hoping for the set.

Once the crank comes back the trans will go out and that pretty much does it for the bottom end.

[754]

Cant sell as a set, because there are many different combinations..

[MRieck]

CB750 main and con bearings are available in the USA no problem.

[slikwilli420]

Looking for the roller bearings for the trans, not the crank/ rod bearings.

[Haybus]

I just got an email from CycleX about trans bearings. I would call them.

Alan

[slikwilli420]

I will get with Cycle X and see what they have. I need to order some other bottom end goodies anyway. I did find a fantastic article on replacing the trans bearings in a '76F which should be the exact same as my '77 engine, but I will make sure to use part numbers from '77 just in case. Here is the article:

https://wrenchandspanner.wordpress.com/2014/12/16/cb750f-transmission-bearings/

It seems like a simple enough process and that will give solid piece of mind when this thing is humming along at 10 grand.

[slikwilli420]

Well the crank has been separated from its home and is packed (very well I might add) and off to Cycle X to be lightened/balanced and have the Cycle X rods installed.





As I dig deeper into the lower end, what do I need to replace and what is just a nice-to-have?

I am definitely planning on the following:
- total oil pump rebuild
- oil seals throughout
- primary chains
- primary chain tensioner
- undercut trans

Things that I don't know if they are necessary:
- lower end roller bearings - how do I tell if these are still good aside from spinning and listening
- drive rubbers behind the clutch

Anything else that falls into either category that I am forgetting?

[754]

HayZuez..that is a box... Bombproof.... A bit bigger than i would have built.
 Takes the worry out of sending it away.
 I usually listen/feel the bearing while slowly turning it...look for roughness or irregular feel.
And sideplay..no excessive play. And no corrossion.

[bear]

In my opinion cush drive rubbers should always be replaced in a competition motor.

Cheers,
Brian

[Retro Rocket]

In my opinion cush drive rubbers should always be replaced in a competition motor.

Cheers,
Brian

With the better rubbers now on offer too....

[slikwilli420]

Any sources besides Cycle x?
In my opinion cush drive rubbers should always be replaced in a competition motor.

Cheers,
Brian

With the better rubbers now on offer too....

[Retro Rocket]

Any sources besides Cycle x?
In my opinion cush drive rubbers should always be replaced in a competition motor.

Cheers,
Brian

With the better rubbers now on offer too....

I'm pretty sure Brian gets his rubber dampers here I Australia, I'm sure he'll chime in soon. There is also someone who sells a complete kit for the dampers, maybe in Germany, if I can find the link i'll post it here...

I was wrong, French, not german...

http://forums.sohc4.net/index.php?topic=119730.0

http://honda60-70s.net/Pieces/23110-300-030_GB/23110-300-030_gb.html

[Old Scrambler]

If your motor has the auto drive-chain oiler, I would remove the little tin tray to delete the oil-feed. Although the K7 was an upgrade, others on this site report the K8 shifter-drum is the BEST. I assume you already have the white tensioner components for the primary and cam chains..............and then there is the consideration for stronger gear-dogs for top-gear.

[slikwilli420]

I will definitely be upgrading all the tensioner wheels for primary and cam. When you say stronger gear dogs do you mean undercut or replacement? Definitely getting the gears undercut.

[MRieck]

Any sources besides Cycle x?
In my opinion cush drive rubbers should always be replaced in a competition motor.

Cheers,
Brian

With the better rubbers now on offer too....

I'm pretty sure Brian gets his rubber dampers here I Australia, I'm sure he'll chime in soon. There is also someone who sells a complete kit for the dampers, maybe in Germany, if I can find the link i'll post it here...

I was wrong, French, not german...

http://forums.sohc4.net/index.php?topic=119730.0

http://honda60-70s.net/Pieces/23110-300-030_GB/23110-300-030_gb.html

A French fella Mick.

[Retro Rocket]

Any sources besides Cycle x?
In my opinion cush drive rubbers should always be replaced in a competition motor.

Cheers,
Brian

With the better rubbers now on offer too....

I'm pretty sure Brian gets his rubber dampers here I Australia, I'm sure he'll chime in soon. There is also someone who sells a complete kit for the dampers, maybe in Germany, if I can find the link i'll post it here...

I was wrong, French, not german...

http://forums.sohc4.net/index.php?topic=119730.0

http://honda60-70s.net/Pieces/23110-300-030_GB/23110-300-030_gb.html

A French fella Mick.

Yep, got that Mike....

[slikwilli420]

Here's the scoop gents. I have made peace with the fact that I cannot afford to finish the motor and the bike ahead of my June deadline. I decided to pick up a good street motor do now I can focus on finishing the other aspects of the bike as well as have the cash to buy riding gear and pay for the race class and entry fees.

Question is what should be done to this street motor before it hits the track? I am planning on a full oil pump seal/spring kit and am pondering a cam chain but won't be splitting the cases. Thoughts on a riveted chain?

Anything else?

[Old Scrambler]

Assuming its a K6 or earlier and you will have a few days of admiring the motor while on your bench before you insert it into the chassis................Cam-chain & tensioner kit; F2 or 41A cam; clean up the casting debri and the intake ports; do the oil-pump mostly for peace of mind; remove the anchor on the left end of the crank & shrink the cover (cut the tail off of the crank); maybe remove the electric-starter gear and motor; get 2 or more L-I batteries (1 for backup) and go total-loss ignition; use the best (high-tensil) drive chain; have a spare clutch-pack; tune and race  

[scottly]

Question is what should be done to this street motor before it hits the track?

If it's a relatively low mileage, stock motor in good condition, I wouldn't do anything more than a good tune-up.

[slikwilli420]

Old scrambler , I thought about most of that although am not going to pull the head since it was just assembled.

I hear the 41a really comes alive at higher rpms and would be a good addition do I'm thinking on that one.

All of the charging/starting bits are going away once I get the motor installed and running.

Cam I do a cam chain and rivet the link so I don't need to pull the engine down? At this point that's the only real option for this motor.

[bwaller]

I have to make the correct length camchains for mine. People suck in their breath but it's fine as long as you do a good job on a true rivot link, not a press type. Tsubaki don't offer anymore but check for DID and whatever CycleX is offering.

[turboguzzi]

I have to make the correct length camchains for mine. People suck in their breath but it's fine as long as you do a good job on a true rivot link, not a press type. Tsubaki don't offer anymore but check for DID and whatever CycleX is offering.

+1, make sure you have a nice, weighty dolly to hammer the pin against

[slikwilli420]

Good thoughts on the cam chain gents. I will talk to Cycle X and see what they can offer. This was a sub-20K mile engine so I may throw caution to the wind since it won't have a high lift cam or stronger springs, but we'll see.

Nothing too outrageous going on other than getting the roller off the bench and on the floor in place of my Vintage Speed Part project, which has been relegated to the back burner for now. Days are coming and going fast on this one.



I have take a number of trail measurements with my 45mm offset trees and with the forks where I think they will be once complete, I am in the 95mm area for trail. I will double and triple check these figures again before I commit to triple trees, but I am close.

I have also filled out the swingarm geometry form from Race Tech for the shocks so that order will be going in soon, along with a spring/emulator kit for the GL forks.

Ideas are flowing for a simple and light seat mount so that will be buttoned up soon as well.

Rearset bracket designs are at the water jet shop now. I am using the approach Haybus used on his racer, with welded tabs on the frame and an aluminum bracket that sandwiches between those to hold the peg assemblies. Should be easy to repair in the event that the rubber side goes up so that will be nice.

[754]

I have to make the correct length camchains for mine. People suck in their breath but it's fine as long as you do a good job on a true rivot link, not a press type. Tsubaki don't offer anymore but check for DID and whatever CycleX is offering.

+1, make sure you have a nice, weighty dolly to hammer the pin against

Just use chain peening tool.

[slikwilli420]

So I talked to Ken at cycle x today and laid out my intentions and he didn't think a new cam chain on a stock motor was necessary so I'll probably just do a cam and sprocket and call it good.

Regarding caliper to spoke clearance, I have about 1/8"at this point. Is that enough or should I design a little more spread into the triple trees?