Topic: 1978 F3 valve angle question

[Gearheadgreg]

Hope i don't get flamed in this area, But just picked up a low mile F3 and been doing some research on the debated death to valve guide's..Back 35 years ago my friends father had been racing a 305 scrambler, It was equipped with Roller rockers AKA "Cam followers" I have been searching for my other bike, and as i read the problems with the side push from the F3 head dynamics, One would wonder why not Rollers could be used to help this problem, and are they available, for the K or F 750 ?  TIA 

[Big Jay]

Are you talking about roller tipped, or roller where the cam rides?

[Gearheadgreg]

Big Jay, it was 1974, long time  Roller "tip" can't remember if it was roller cam ? i guess my question is has anyone ever seen these, This site is geared towards hardcore motorheads and racing, i have asked on other MC sites being my Valk is very similar in rocker design, the only thing i could come up with is welding a roller tip to the existing rocker, read reply # 3 http://wildguzzi.com/forum/index.php?topic=39313.0 

[kos]

You won't get flamed for asking, but all SOHC CB750 Hondas from 1969-1978 KO-F2 (there never was a F3 designation in USA model line up) used the same rocker/cam towers, the same rocker arms and thus the same valve angle in the head is used.

End of this story.

KOS

[TwoTired]

I asked a similar question years ago.

To alleviate the valve guide wear, you need a roller on top of the valve stem.  This is also where the clearance adjuster is.  So, no only do you add a roller, but a mechanism to adjust the clearance.  I've never seen one to prove existence.

The added roller and the adjustment complexity adds weight to the valve train, which is a nemesis for high revving engines.

With enough money, engineering, and machine work, anything is possible.


I have NO trouble believing you have an F3 model and they were certainly sold in the US.
The F model Cb750 was introduced in 1975 as the F0, 1976 was the F1, 77 the F2, and 78 the F3.  All these models were available and sold in the US.

I have both and F2 and an F3.

The Honda shop manual supplement (group 27) clearly defines the F3 as engine number CB750 - 2200001 and subsequent, Frame number Cb750F - 3100002 and subsequent.

Cheers,

[Gearheadgreg]

Well so much for the Roller tip...gonna give it a rest, thanks for the info.....But the F3 # chart has me a little confused ? my Eng id # is 310000, according to this info somebody did a misprint and several other sites also, they state after the eng id # E or F could be common ? http://www.hondachopper.com/engine/engine_mods/modifications.html

[Gearheadgreg]

You won't get flamed for asking, but all SOHC CB750 Hondas from 1969-1978 KO-F2 (there never was a F3 designation in USA model line up) used the same rocker/cam towers, the same rocker arms and thus the same valve angle in the head is used.

End of this story.

KOS

Thanks for the info, how about a link or thread of what was available in the states before i make more of a fool out of myself ? TIA also my understanding was the F3 valves were moved up into the head to allow clearance for larger valves, being more like a open chamber, dome type piston to be used, for that reason the rocker angle was changed ?  but retained same valve train..thus to be the problem ?

[TwoTired]

Well so much for the Roller tip...gonna give it a rest, thanks for the info.....But the F3 # chart has me a little confused ? my Eng id # is 310000, according to this info somebody did a misprint and several other sites also, they state after the eng id # E or F could be common ? http://www.hondachopper.com/engine/engine_mods/modifications.html

What I printed above is what the Honda shop manual states.  However, the Honda Motorcycle Identification Guide lists the 78 CB750 as:
Frame CB750F - 2200001 ~
Engine: CB750FE - 3100001 ~

The Honda Parts Fiche agrees with the Honda I.D. guide (rather than the shop manual), and shows the same head used for both 77 and 78 models.
There is a Honda code change for the head.  It is my understanding that later heads had hardened valve guides installed as a means to retard rapid guide wear.  There were many heads that had the guides changed under warranty.  I have a friend that did many of them while he was still a Honda Mechanic "back in the day".

My 78 is currently at the Corbin factory, so I can't look at that bike's numbers right now.

The head chamber for the F2/F3 was domed to accept larger valves.  The piston had to be domed to retain Compression ratio.  The doming of the chamber increased the valve stem angle, and the side loads that the rocker placed on the valve stem throughout it's movement arc.

It is not just the guides that wear.  The adjuster tip puts a divot in the valve stem tip, as well as mushrooming the adjuster tip.  Grinding the valve stem tip flat, changes the valve geometry (for the worse).  Mrieck found "lash caps" to restore the valve overall length and maintain the proper geometry.  Almost certainly, the valve face and seat need regrinding if the guides have worn bad enough to yield an oil smoke out the exhaust issue.

A roller/adjuster at the valve would certainly help the longevity of the valve guides/valves, if only it were available.

I once toyed with the idea of putting concentric cams at the rocker pivot for adjusting clearance.  Then adding the rollers to the rockers at the stem interface.  Works in concept, but the cost will probably not make it very "popular". 

Cheers,

[Gearheadgreg]

I guess i will just have to enjoy my F3 my frame is #22557816 motor #3157817 looks like they match 78 is the correct year motor and frame...The CB750F'78 750 Super Sport was sold in 1978 and was available in one of two colors: Candy Presto Red or Black. The gas tank stripe was red with gold pinstripes. The "750 FOUR" side cover emblem had a new graphic design. The exhaust was a 4-into-1. The gas tank, side covers, and rear cowl were the basic color (red or black). The wheels were comstar with dual front disc brakes and a single rear disc brake. The engine and fork legs were black. The engine was a 736cc SOHC 2-valve air-cooled inline 4 cylinder linked to a 5-speed transmission and chain drive.

    * Serial Number
          o Frame: CB750F-2200001
          o Engine: CB750FE-3100001
Also this link>page (57)..http://docs.google.com/viewer?a=v&q=cache:SC8upKKBw2YJ:kreigenbrink.com/app/download/3124642202/197883.pdf+1978+Honda+F3+super+sport  also this talks about the larger valves as you spoke about looks like  my new purchase was a good find....i had no clue what it was the day i bought it LOL!! http://vintagemotorcyclesonline.com/features/bike-of-the-month/133-1978-honda-cb750f3

[Gearheadgreg]

Two Tired, thanks for your info,,, BTW Corbin has your bike..I will also be purchasing the soloF seat thanks for making this happen with Corbin,,i just seen your thread today and i am stoked!! almost went to the upholster guy today but stopped just in time>