Topic: 750K2 Hot Rod Revival - Early Christmas

[CBJoe]

The engine mod list is impressive. How far are you spinning it?


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Thats for some debate....I let the dyno guys spin it too high I think....up to 10.5K RPM.  To be honest I really haven't had a chance to get a great feel for the bike as it hasn't been ridden much since finishing all the wiring and putting the RS34s on it.

It pulls very hard from 7.5-9K rpm from a butt dyno.

Engine was built by member MRieck...and if the top end ever comes off for refresh he'll get it back.

Joe

[scottly]

Still a few issues to sort out...I'm still having the starter clatter at times...I've done the following:

- Installed a Starter Gear from Scottly that had the contact face machined smooth
- Installed a Starter Gear from Bill Bentons Stash
- Installed New Rollers and Springs

Can a bad starter cause the same symptoms?  Or am I just unlucky with starter gears?  The rotor bolt is still plenty tight

Cheers, Joe

The only thing you haven't changed is the clutch "hub" itself? What oil are you using?

[CBJoe]

Hey Scott...upon recommendation I’ve been running Motul 300V Synthetic Motor Oil - 15W50 since acquiring the bike.


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[PeWe]

Alternator sit tight on  crankshaft?
What about the oil seal if that is flipped?
I had some thoughts when installing them as the old before.

I have used Motul 7100 15W-50 synth with no starter issue.
Now Red Line also an esther synth.
It can miss sometimes as it occasionally could back in the early 80's. It use a stronger motor from CB900, 800W.

[CBJoe]

Hi Pewe....alternator is tight on the crank.

By oil seal do you mean the crank seal?  I have not changed this seal, so it’s the same as when mike built the engine 12 years ago (hard to believe it’s that long ago).

Can someone tell me it a weak starter could also cause similar symptoms as a slipping starter clutch? Or would it just be a slow crank?

At the moment this issue isn’t high on my list, so it will be a bit till I do any actual work on it.

Joe


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[PeWe]

The seal that sit inside the starter gear. Item 17
https://www.cmsnl.com/honda-cb750k5-four-1975-usa_model483/partslist/E++11.html#.XqBri7eeyKo

I do not know if this can cause starter gear slip, I guess so.
Oil seals job is to keep oil on one side only.

Where the lips points at decide that.

[CBJoe]

The seal that sit inside the starter gear. Item 17
https://www.cmsnl.com/honda-cb750k5-four-1975-usa_model483/partslist/E++11.html#.XqBri7eeyKo

I do not know if this can cause starter gear slip, I guess so.
Oil seals job is to keep oil on one side only.

Where the lips points at decide that.

To be honest I never changed the seal...I just left the ones that were already in the gear I used.  At this i'm just going to run the bike and see if the clatter is consistent and see how it behaves when hot.  Worst case I'll just get a whole starter clutch/hub pair from somewhere.

i'm going to double-check the valve clearances and do some general tune up stuff and then will try and get some miles on the bike.

I really want to replace the old stock rims with a new set.  I think the old rims/tires are a bit out of True/balance as I get some vibrations at speed.  Not sure if I'm going to keep the stock rim sizes or do something different. 

Anybody got a nice set of rims to sell me?

[PeWe]

Verify pressure in tires.
Too high is not comfortable.
I inflate mine as Honda label say. Front 2.1, rear 2.4 BAR

[RAFster122s]

Might be a bit of flat spotting going on from sitting that will correct a little when the tires get some heat in them. Or, they need time on the trying stand to get them tighter to running concentrically as well as side to side true.
Good set of Excel, Sun, or similar aluminum rims would lower your rotating mass as well. Just keep them inflated well so any expansion joints don't beat them to death. I realize they were redoing the interstates but lots of roads in the Midwest with similar frost cycle damage...besides, super slabs are no fun to ride on...

[CBJoe]

Doing some thinking about Rims as they are on my list...doing some reading through the forums and it seems running 18" on both the Front and Rear has good results. 

Currently the bike is running stock rim sizes with the following tire sizes.  Visually I'm just fine with the look.

Front - 1.85x19 40 hole - 100/90/19
Rear - 2.15x18 40 hole - 120/90/18

Looking for some thoughts on an 18" vs 19" front and sticking with stock widths or doing something different specifically for handling.

Cheers, Joe

[MRieck]

Doing some thinking about Rims as they are on my list...doing some reading through the forums and it seems running 18" on both the Front and Rear has good results. 

Currently the bike is running stock rim sizes with the following tire sizes.  Visually I'm just fine with the look.

Front - 1.85x19 40 hole - 100/90/19
Rear - 2.15x18 40 hole - 120/90/18

Looking for some thoughts on an 18" vs 19" front and sticking with stock widths or doing something different specifically for handling.

Cheers, Joe

I'd go with an 18" front and rear. 2.5" on the rear to get a 130/80 on there. I think I have a 2" X 18 for a front unit.

[slikwilli420]

I run a 2.5 front and 3.0 rear on my race bike with 110 and 130 tires. 2.5 is too skinny for a 130 tire in my opinion and many tire manufacturers would agree. The 18s front and rear in those widths expands tire options and gives it a great look with solid handling.

[PeWe]

I had a Metzeler ME-99 130/80-18 on my stock 2.15" rear rim end of the 80's.
Mostly touring. 
I had to bend the brake stopper arm in an S shape to avoid the tire.
I could have mounted arm more to the right on swing arm with spacer where arm sat before.

I have noticed that stock 4.0" tire work better on stock 2.15" rim, 3.25 on 1.85" front. Handling as well as milage compared to 120/90-18. Easier to remove/ mount stock chain guard with 4.0" tire. This is slimmer, more like a 110.
Front 3.25 is a new experience.
My K6 feels stable and quick into the corners with new stock tires. No racing, only country roads

3.25" easier to mount front.
I had a 3.50"-19 tire on stock 1.85 front rim many years ago that had to be pressed on the bike. I think the left fender bracket or caliper was tight when wheel went on.

It is enough of work today on my K6 with dual brakes and the right brake have to be removed before wheel goes off. With a really wide tire, left caliper bracket must off too, and back when wheel is back on?

[CBJoe]

I run a 2.5 front and 3.0 rear on my race bike with 110 and 130 tires. 2.5 is too skinny for a 130 tire in my opinion and many tire manufacturers would agree. The 18s front and rear in those widths expands tire options and gives it a great look with solid handling.

Do you know if those sizes will work with stock front and rear end setups?

[Jerry Rxman Griffin aka MuthaF'er]

Joe, what about a lower profile 19" front tire? 100/80/19? Available?

[slikwilli420]

I run a 2.5 front and 3.0 rear on my race bike with 110 and 130 tires. 2.5 is too skinny for a 130 tire in my opinion and many tire manufacturers would agree. The 18s front and rear in those widths expands tire options and gives it a great look with solid handling.

Do you know if those sizes will work with stock front and rear end setups?

That I cannot speak to personally, but I don't see why not. Neither of those widths is a massive departure from stock. I have run a 110 front and 130 rear on stock widths and it all fit. The right rim width is about getting the sidewall to sit at the right angle so the tire carcass doesn't flex too much. Those widths are a better match to the physical size of the 750 as compared to the skinny stock widths. As long as the tire and rim match from a compatibility standpoint, that is really what matters. But I don't think clearances will be an issue with either.

[MCRider]

Joe:
I forget if you have twin discs? If you'll remember on Phaedrus, we have a 2.15 x 18 on the front. It has a CB350F front fender which looks all the world like a CB750 fender except its proportionately smaller, tighter radius, etc.  You have the most miles on it, so you could answer the handling problems if any. 

We have to loosen one caliper and deflate the tire to get it out from in the fender and mounting bolts.

I'm using a 3.5 x 17 on the rr, with a 140/70x17 rr tire. Requires stepping the brake stay out a little.

[CBJoe]

I forgot you had a 3.5 rim on the rear.....and no...I didn't notice any handling issues

I don't have twin disks yet...but its in the plan for the future....hopefully

[PeWe]

Twin discs a must.
My K6 got more than double brake power with 2 CB750 stock type brakes.

[scottly]

Hey Scott...upon recommendation I’ve been running Motul 300V Synthetic Motor Oil - 15W50 since acquiring the bike.


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The reason I asked about the oil was someone had just stated on a different thread that using synthetic oil caused the starter clutch to slip. You might want to try the Spectro HD oil that Ofreen uses?
Also, if the oil smoke issue comes back, check to see if there is sufficient drainage from the top of the head. Are there heavy duty studs installed? 

[MRieck]

I run a 2.5 front and 3.0 rear on my race bike with 110 and 130 tires. 2.5 is too skinny for a 130 tire in my opinion and many tire manufacturers would agree. The 18s front and rear in those widths expands tire options and gives it a great look with solid handling.

I have to correct myself as memory got the better of me. I currently have the same set up Matt has listed here. It has worked very well for about 25 years.

[PeWe]

I run a 2.5 front and 3.0 rear on my race bike with 110 and 130 tires. 2.5 is too skinny for a 130 tire in my opinion and many tire manufacturers would agree. The 18s front and rear in those widths expands tire options and gives it a great look with solid handling.

I have to correct myself as memory got the better of me. I currently have the same set up Matt has listed here. It has worked very well for about 25 years.

I can't help to enter this question too.

- 110/80-18 front will fit a K2-K6 fork, stock fender?
(100/90-19 used with no issues)
Tire has not much air when mounting the wheel, right?

130/80-18 rear has been used before on my bike. Maybe I had to massage the stock chain guard a little.

- Will 130/80-18  on 3" rim have wider tire area against the road than stock?

I have understood here that these tires + rims should work.

My rear tire disappear very quick
120/90-18 on 2.15" rim flattened out at around 4000km with snake handling in light corners. 4.0-18 better.
One tire got bad handling after only 3500km.

Racers have opposite "problems" when tire sides wear faster then center, right?

The fatter tire on a wider rim will be better?
130 rear need a matching front so 110 there for ok handling in corners, right?

I have a front hub, time for another rear hub , rims and spokes for an extra setup of wheels if doing this.

[PeWe]

I just noticed one detail.
K2-K6 fork with dual stock brakes can not have wider 18" wheel.
Caliper bracket upper part will hit the rim.

Modification of caliper bracket needed. Use another bracket like a real right hand bracket might fix it. If they exist.

Much space on left side.

I guess that an F bike with F dual brakes has more clearance and work better for 18" wheel.

[MRieck]

I just noticed one detail.
K2-K6 fork with dual stock brakes can not have wider 18" wheel.
Caliper bracket upper part will hit the rim.

Modification of caliper bracket needed. Use another bracket like a real right hand bracket might fix it. If they exist.

Much space on left side.

I guess that an F bike with F dual brakes has more clearance and work better for 18" wheel.

I have the F2 forks and calipers with modified F rotors and a spacer. Hub is Helicoiled for flat head Allen bolts.

[scottly]

Copper tubing is not allowed for hydraulic brake plumbing!!! It is prone to cracking from fatigue.