Topic: CB750 AHRMA Sportsman 750 Racer

[754]

I made a collar to go against side of case , thinking with the starter parts off, there is nothing to slow the oil down coming out of the main bearing.. Was worried about pressure loss. Same collar can cover oil hole, or you can weld the hole.
 Some guys dont run a cover over the crank, just a seal plate..

[slikwilli420]

Thats a good point Frank. I would need to figure out how to seal the collar so oil didnt come out as in the pics from others bikes. Cutting an internal o-ring groove might be tough. I guess I could come up with a seal as well.

[Jerry Rxman Griffin aka MuthaF'er]

Pressure. How much pressure would you lose with the hole wide open and not possibly controlled by the starter clutch? 

[754]

I think my cover was tight against the case, just gasket holding it on. I made a thin sleeve with a lip to cover crank hole, but made a puller to get it off.
I had it so it did not cover the complete hole, and bike was not starting.. Surprising how much oil came out just kicking it..

[slikwilli420]

Points well noted! That's why I ask here so I am SURE. I will go ahead and make the collar to block off that hole.

[754]

What i made looked like a speedi-sleeve.
Are you going to run the snout cover, probsblye better for roadracing.

[scottly]

There will be no loss in pressure with the starter gear removed, as there is a restriction in the crank hole. The starter gear is not a tight fit on the crank, and there are channels to drain any oil. The bolt hole in the end of crank for the rotor absolutely needs to be plugged, though. It's a straight shot to the main bearing oil galley.
 

[Haybus]

Those are pics of my kluge setup. I was worried about pressure loss so I capped off the crank end. My pit mate simply cut off the crank end and pressed in a plug. That's a much cleaner look, but makes for a specific crank to that motor (no crank exchanges). The hole running lengthwise through the crank is very small, indeed. I would guess there wouldn't be much pressure loss by not capping off the end, but I wasn't willing to find out with a high dollar motor.

Alan

[scottly]

The hole running lengthwise through the crank is very small, indeed. I would guess there wouldn't be much pressure loss by not capping off the end,
Alan

The hole running lengthwise is huge compared to the tiny orifice for the starter gear, and would cause a massive loss of pressure if left uncapped!

[slikwilli420]

I'll see if I can find a replacement  bolt for the end. For the side orifice, could I drill/ tap for a grub screw or just let that oil fling and drain back?

[scottly]

I tried to tap the side hole for a grub screw, and promptly snapped off the tap, which sealed the hole very well. However, if I ever want to re-install the starter, I'm going to have to spent a fair amount of time with diamond bits in a dremel to remove the broken tap.
It's not necessary to block the hole; I ran my bike for years with it open, but there are easier ways to block it, such as Frank's sleeve, or fitting the inner race of a bearing with a 25mm ID, which IIRC was Voxonda's idea. If you make a sleeve out of aluminum, it will have to be a tight shrink fit, where you heat the sleeve to expand it to install it onto the cold crank, since aluminum expands more than steel with heat.
For the bolt, it might not hurt to fit a copper washer under the head, as well as some regular strength lock-tight. It won't need to be torqued nearly as tightly as the bolt that locks the rotor onto the taper.

[754]

I think of the shoulders of the crank throw dont have one here but i think they go full circle, and slow oil flow out of the mains.  The block off cover , make the hole a bit bigger than the crank, now it is a gasket width from the main bearing, solves that problem.
 Scottly, if needed for e start, simply drill a new hole. Myself I want the hole covered, if there were not a seal on the steel starter gear, I would worry about it less.
 As for the end bolt, make an aluminum shorter lighter one..

[scottly]

There is only a seal on the rotor side of the gear, evidently to direct the flow between the gear and crank case, instead of into the cavities in the starter clutch. No clutch, no worries.

[754]

I think the oil will take the easiest path, and that hole is easier to go thru than the journals with 1-2 thou clearance.
Seems that way to me...any potential loss of pressure should be looked at..

[scottly]

The bushing in the starter gear has more than 1-2 thou clearance, so it isn't a restriction. If you want every drop of oil to go to the bearings, then block off the hole, but it's not going to cause a pressure loss if left open. If you want to run a starter again, make sure what ever you do is easily reversible, instead of snapping off a tap.

[scottly]

I'll see if I can find a replacement  bolt for the end.

The thread size is m12x 1.00, and should have a shank length of about 20mm (the threads in the crank are recessed about 9-10mm).

[slikwilli420]

Still making some great progress on a bunch of bits. First is finishing up the crankshaft end cover. Its finally welded and ready for action. All that is left is to make a sleeve to press over the OD of the crank to block the side oil hole and find a lighter M12-1.0 bolt for the end.



In order to get enough space for the caliper to clear the spokes, I had to come up with a spacer for the rotor, which is an FZR600 item. The spacer can likely be lightened more, but here is the initial shot.



Spacing for the forks to keep the wheel centered is 8 inches, which is a bit wide but shouldn't hurt anything.

The axle is a hollow CBR item, which I am using front and rear, since the front was converted to 20mm bearings. Here is a shot of the modified axle and spacers.





The axle spacers still need some finish work as does the rotor spacer, with an eye to lightening everything but keeping it safe.

Now that I have spacing established for the forks, I drew up a few versions in different offsets for the triple clamps. I still need to work out geometry with different offsets before I settle but wanted to play around some. The top will be 3/4" while the bottom will be 1.5-2.0 with lots of relieving for weight savings, but I do want something very stout for the front end.

Here is an overall frame shot with tank and seat I plan to use.



Last are the frame gussets I designed. They are 18 gauge steel. I made the dimple die from aluminum since it was only getting used a couple times and it worked flawlessly. I will be looking into some x-bracing near the swing arm and some more near the neck. I am still debating moving the upper frame rails like livefast_dieold did or doing a frame kit. The problem with a frame kit is weight. More to come there.



I am kind of bouncing all over on this and my mind has gone to the carbs. I need to use round tops and need to do more investigation on  what I can do to them internally. Does anyone have experience boring these out? I'm wondering if this is something I can just jig up and use a boring head on my mill to take a mm or two out of the throat. Are there mods to the slides that will help? Any thoughts here are much appreciated, since I think this will be the most restrictive part of the engine by far.

[754]

Nice gussets.. Frame kit only weighs about 475 grams including the box..
Your alternator cover, why not make the snout outof one piece, or put it together with threads...which wouold then be hidden..?

[Haybus]

Is that the rotor you're planning to run? The rules say fixed, and that's floating. I've never raced AHRMA so maybe they'll allow it?

j) Sportsman 750 machines may use one front disc brake; period-type fixed steel disc, maximum diameter 12 inches, two-piston caliper. Sportsman 750 machines may use a period-type rear drum brake or period-type rear disc with a two-piston caliper.

[slikwilli420]

Nice gussets.. Frame kit only weighs about 475 grams including the box..
Your alternator cover, why not make the snout outof one piece, or put it together with threads...which wouold then be hidden..?

Frank, I didn't have a piece of aluminum that diameter so I made it two pieces instead. Could have gonee either way I guess.

[slikwilli420]

Is that the rotor you're planning to run? The rules say fixed, and that's floating. I've never raced AHRMA so maybe they'll allow it?

j) Sportsman 750 machines may use one front disc brake; period-type fixed steel disc, maximum diameter 12 inches, two-piston caliper. Sportsman 750 machines may use a period-type rear drum brake or period-type rear disc with a two-piston caliper.

Floating in AHRMA means it moves when you push on it. No full floaters. This one is very solid and is the standard for what guys use on this class. AHRMA rules can be a bit vague but I am working with my uncle who is a multi time champ of the sportsman class to make sure I don't overstep.

[bwaller]

That's great if that type disc is allowed but it surprises me! Usually AHMRA is tougher than most and the two assn's I race in wouldn't allow. It's good to know someone on the inside when setting a bike up for a class.

In my case I was told no Keihin CR's so I spent a fortune building a good set of Mic smoothbores. Now CR's are everywhere.  Different tech chairmen and that's ok!

[slikwilli420]

The rules are a bit tough to navigate so I do agree having someone that has been doing it for almost 10 years is very helpful. Most of the time no one makes a stink unless you start blowing everyone else out of the water.

My concern with carbs is needing to stay with stock round tops, although there is no mention in the rules about internal modifications. I need to get some stock carb gurus in here to help me out on that one.

[bwaller]

The concern is always that they appear same as stock. In the case of round top carbs, I wouldn't worry. If they allow floating discs when they ask for solid, they shouldn't worry about internal carb work done if they appear completely stock.

[Haybus]

Glad you have an "in" to the rules. That cover looks familiar!! Nice looking welds too.

Alan