Topic: Valve guide bore on 750F2/F3?

[wohali]

Hi SOHC Fans,

None of the shop manuals I have (Honda, Clymer, Haynes, Hondaman) list different valve guide bore (ID) values for the F2/F3 era bikes. I know from my readings that these bikes were notorious for wear here, due to the altered angle on the cam. Stem-to-guide clearances of 0.05 (intake) and 0.08 (exhaust) seem to be the recommended maximums. 

Well, this bike certainly is worse than that on the exhaust side... Does anyone have measurements I could compare mine against? Are the exhaust guides just that bad?

My '78 CB750F3:
Typical intake valve stem OD: 6.59-6.60mm
Typical intake valve guide bore ID: 6.63mm
Stem-to-guide clearance: ~0.03mm (OK)

Typical exhaust valve stem OD: 6.56-6.57mm
Typical exhaust valve guide bore ID: 6.95-7.10mm
Stem-to-guide clearance: ~0.55mm

Guess I'm getting new (brass) guides from Dynoman...

[MRieck]

Hi SOHC Fans,

None of the shop manuals I have (Honda, Clymer, Haynes, Hondaman) list different valve guide bore (ID) values for the F2/F3 era bikes. I know from my readings that these bikes were notorious for wear here, due to the altered angle on the cam. Stem-to-guide clearances of 0.05 (intake) and 0.08 (exhaust) seem to be the recommended maximums.  

Well, this bike certainly is worse than that on the exhaust side... Does anyone have measurements I could compare mine against? Are the exhaust guides just that bad?

My '78 CB750F3:
Typical intake valve stem OD: 6.59-6.60mm
Typical intake valve guide bore ID: 6.63mm
Stem-to-guide clearance: ~0.03mm (OK)

Typical exhaust valve stem OD: 6.56-6.57mm
Typical exhaust valve guide bore ID: 6.95-7.10mm
Stem-to-guide clearance: ~0.55mm

Guess I'm getting new guides ...

Yes. You are. They are not brass either. Check out CycleX....their guides are a known piece.

[wohali]

These ones, eh?

In your opinion, are these measurably better than the other vendors out there, such as KPMI, APE or Dynoman (http://www.dynoman.net/engine/valve-guides.html) ?

CycleX makes some pretty strong claims about their F2 head parts, including the spring retainers (first I've heard that they're prone to failure) and their valves. I don't mind shelling out money to redo the head - I'm not planning on taking the engine part many times a year - but $400 in parts + shipping + import tax seems a bit much on something that was running mostly fine when I took it out of service.

And sorry, not brass, I meant Oilite....or nickel bronze...

[brandEn]

Sticker shock! I just ordered the Cycle X 836 kit for my F3 and I am going to be getting their top end parts as well here shortly. Its a tough pill to swallow for sure. Had I known about all the issues this F model has as far as parts being available and being the black sheep of the SOHC's I would have rethought my decision and waited for a K model.

[tweakin]

Sticker shock! I just ordered the Cycle X 836 kit for my F3 and I am going to be getting their top end parts as well here shortly. Its a tough pill to swallow for sure. Had I known about all the issues this F model has as far as parts being available and being the black sheep of the SOHC's I would have rethought my decision and waited for a K model.

Shame on you talking bad about the 750f, lol.  I didn't know better at first but now I am more than happy with my decision to get the F. 

[brandEn]

easy for you to say your bikes done! lol

[wohali]

No desire to overbore just now - the 836 will come later, when the cylinders actually NEED to be bored, not just honed - I am mostly concerned now about whether these retainers really ARE that weak, and if so, if I shouldn't just replace everything at once (and have the valve seats recut at the same time for the new valves).

The bike cost me next to nothing on CL 5 years ago, and I've learned so much riding it (my first bike!) and working on it I really can't complain about the cost...it's more of a question of whether I should be alarmed/worried about the retainers failing or not.

tweakin' did you get the full set of CycleX top end bits too? Or did you go full 836 with the new cam, or keep it stock?

[tweakin]

All my head parts were from cycle x, high flow valves, guides, springs and retainers.  My pistons are forged JE pistons made for the 750f by dynoman and I have a webcam 41 grind for the cam.  I also completely rebuilt the bottom end with new bearings and such.

Keep up the great work.

 

No desire to overbore just now - the 836 will come later, when the cylinders actually NEED to be bored, not just honed - I am mostly concerned now about whether these retainers really ARE that weak, and if so, if I shouldn't just replace everything at once (and have the valve seats recut at the same time for the new valves).

The bike cost me next to nothing on CL 5 years ago, and I've learned so much riding it (my first bike!) and working on it I really can't complain about the cost...it's more of a question of whether I should be alarmed/worried about the retainers failing or not.

tweakin' did you get the full set of CycleX top end bits too? Or did you go full 836 with the new cam, or keep it stock?

[Gearheadgreg]

No desire to overbore just now - the 836 will come later, when the cylinders actually NEED to be bored, not just honed - I am mostly concerned now about whether these retainers really ARE that weak, and if so, if I shouldn't just replace everything at once (and have the valve seats recut at the same time for the new valves).

The bike cost me next to nothing on CL 5 years ago, and I've learned so much riding it (my first bike!) and working on it I really can't complain about the cost...it's more of a question of whether I should be alarmed/worried about the retainers failing or not.

tweakin' did you get the full set of CycleX top end bits too? Or did you go full 836 with the new cam, or keep it stock?

I have only heard 1 story that is credible in my opinion, They where testing the F3 for a Motorcycle RAG (magazine) running it down the strip all day at full throttle,,,,finally it dropped a valve,after looking into,,, was a defective part on that bike, The valve guide wear is true, you will notice smoke on start up,replace the guides as you are doing will be money well spent, as soon as you twist the Throttle on the F3 you will be glad it has the larger valves,, runners,,Cam ect...i have a pristine F3 that was sprayed with WD 40 16 years ago and put in a heated garage and covered with 16.000 miles...No smoke no noise from the top end just needed Carb gaskets and jet cleaning,,,THE BIKE FLAT MOVES!! btw Great job on your attention to detail, been watching your build, fantastic!!