FRANKENHONDA II the 1982 DOHC CB 750F2 Build

The Jimbonaut

Active Member
What engine oil are you using? If you're going through a lot at the moment you might want to look into Rotella T4. It's formulated for diesel engines but don't let that put you off. The weight (15W 40) is good for our engines too and is formulated for wet clutches. I got turned on to it by a lot of bike guys as a much cheaper alternative to the more expensive moto-specific oil. Used it ever since on all my bikes and never had a problem.
 

cb250nproject

If you can make it better do so
Just using this
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20/50 is what the manual says,

So today I took the cam cover off, backed off all the cylinder stud nuts then re-torqued them in the correct sequence. I did them up to 15 ft lbs first then a second pass to 30ft lbs
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Once I re-torqued the head and put the cam cover back on I, put some Honda bond around the out side of the gasket where the leak was. It’s grasping at straws but Rex said give it a crack.

I’ll let it sit overnight before starting it and maybe getting a test ride in.

I noticed when I was out riding yesterday at certain speeds it kind of felt like the forks were bouncing or vibrating. Today when I hopped on I pushed the bike forwards then used the front breaks, I reckon there was the slightest bit of play, so I’ve tightened the triple stem.

See how she all goes tomorrow.


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The Jimbonaut

Active Member
Don't take my word for it (I wouldn't either truth be told!) but consider the torque on those head bolts. If you haven't already then I'd join the cb1100f.net forum (it's dedicated to Supersport model CB's) and ask what the consensus is on torque specs. I couldn't say if the extra 5ft lbs will fix your problem but the guys over there may well be able to. Could be helpful.
 

Maritime

Well-Known Member
I was going to say 50W is overkill but then remembered where you live. Gets much hotter there than here.
 

cb250nproject

If you can make it better do so
Don't take my word for it (I wouldn't either truth be told!) but consider the torque on those head bolts. If you haven't already then I'd join the cb1100f.net forum (it's dedicated to Supersport model CB's) and ask what the consensus is on torque specs. I couldn't say if the extra 5ft lbs will fix your problem but the guys over there may well be able to. Could be helpful.
Yea I had a long convo yesterday with Rex, he was actually getting custom gaskets made out of copper I believe then using the honda bond... I just hope today that she’s sorted I went up to 30ft lbs in sequence and it felt like it pulled down with even tension across all the studs. But once oil has found its path it will be hard to stop I’d imagine.


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cb250nproject

If you can make it better do so
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well it’s leaking less but it hasn’t stopped :/

The steering felt a lot better and I could feel the power coming a bit more now. The bike steering feels very responsive, I should work out the rake and trail to see what I’ve done to it


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teazer

Active Member
DTT BOTM WINNER
And warp the head and stretch the studs....... Too much torque is worse than not enough - as a rule.

If the head is leaking, pull it off and find out why. It's possible that the head or block are warped or scratched but more likely that an 'O' ring around one of the studs is out of place or thinner than the gasket - allowing oil to seep out. Might even be missing some thin metal sleeves that look like thin wall dowel pins.
 

teazer

Active Member
DTT BOTM WINNER
And yet a TZ350 that makes almost as much power as that bike holds its fluids in with more like 15 foot pounds of torque. Different beast of course, but large heads tend to warp when they are that tight and should not leak at close to that torque. My CB900F with high comp pistons never leaked a drop and I don't remember tightening it that tight. That was a long time ago though.

But we all have a different approach. I prefer the least amount of torque on any bolt - consistent with the FSM of course. Others have a different approach and I'm not telling anyone what they must do. Just suggesting that if it leaks, there is a reason. Find it and fix it.

Removing the top end on one of those motors is a complete PIA, but if he does it, he'll be able to see what's wrong and can check the head and barrel for flatness. And easy way is to clean both faces and wipe a thin layer of bearing blue on one face and then place the head on top of the barrel. Then remove it and see where they touched and where they didn't.

A common problem with doweled Hondas is the dowel is too long and stops the head from pulling down flush with the barrel. That's especially true if head or barrel have been machined. Fortunately that's easy to fix if the head is off.
 

The Jimbonaut

Active Member
Not questioning your approach at all, in fact that all sounds like excellent advice. All I'm saying (actually, what I've been told by others that know a f*ckload more than me about this kind of thing) is that the FSM (and Clymers for that matter) generalizes over the models, and does not give specific torque specs for the different studs we have in our F model bikes.
 

Maritime

Well-Known Member
Not questioning your approach at all, in fact that all sounds like excellent advice. All I'm saying (actually, what I've been told by others that know a f*ckload more than me about this kind of thing) is that the FSM (and Clymers for that matter) generalizes over the models, and does not give specific torque specs for the different studs we have in our F model bikes.
My guess is there is a bulletin for the F bikes Honda would have sent to dealers etc for the difference.
 

cb250nproject

If you can make it better do so
Well I hit everything with degreaser, went for another test run

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Well it kind of looks like it’s stopped, I’ve had to go away for a few days of work, so I’ll see what happens when I take it out again.

Now another thing I did was measure my trail it was 11cm or 4.33” I think and from what I recall, stock was 3.96” so I’ve increased the trail. The forks are shorter and the wheel is a 17” not 19”, now the rear is a 17” not 18” which was stock and the ohlins are standard for the bike so that hasn’t changed.

I’m not sure if that’s right or not, increase in trail should make the bike less responsive? Under heavy acceleration the steering was feeling a little light. I’m not sure if I need to stiffen up the rear or not.

I’m going to have to call in a prp to get the static sag set


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cb250nproject

If you can make it better do so
So it turns out convincing the wifey to drive down the road at 40km h while I calibrate the speedo has been one tough sell.. in fact I had to leave for work luckily only for a few days so hopefully Friday I’ll get it sorted.

I believe the speedo is reading slower that what is the actual speed is, so perhaps I’ll use the “well who’s going to pay for my ticket?” Approach


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pidjones

Active Member
Most Hondas read 5 - 10% fast. 70s and 80s the worst. But, even my '06 GL1800 reads ~ 5 - 7% high. My '79 CB750F and '78 GL1000 speedos both had to be opened and the needle bearing lubed with a fraction of a drop of silicone spray lube. That freed them up and they began reading their normal optimistic Honda + speed.
 

cb250nproject

If you can make it better do so
With a last name like Murphy if I jerry Righto something to hold my phone to the bars, I’m pretty sure I’ll come home with no phone, but if I get desperate I’ll probably give it a go


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