Topic: CB750 F2 Valve Guide Removal

[CB750F2]

        I need some advice. I will shortly be replacing the valve guides on my CB750 F2. I have removed the circ clips on the camshaft side of the guides. It looks as if I can then punch them through from the camshaft side through to the combustion chamber. Is this correct? I have checked other threads which indicate that the ends of the guides on the combustion side need to be bead blasted to remove any carbon buildup that would cause scouring of the valve guide bore when driven out from the combustion side.  Some of my guides appear to be loose because they can be moved with just a light tap with a drift and there is evidence of oil seeping down between the exhaust valve guides and head in the combustion chamber.
        My intention is to replace the guides with the bronze ones either from APE or Dynoman. Are these guides oversize so that they will be a tight fit when installed? I can see that the bronze guides have a shoulder and don't require the circ clips. To replace these they would certainly have to be driven out from the combustion side or  - like 754 does - drill the top off and then drive them out from the camshaft side.
       One more question. Is it a good idea to fit valve stem seals on the exhaust side? I am inclined to think that it would be better to leave the seals off so that the valve stems can be lubricated resulting in less wear. Particularly with the F2 motor.
Thanks, Pat

[MCRider]

IINM, you'll need to recut the valve seats after installing guides as the valves will be ever so slightly (or more than slightly) off their seats with the new guides. The whole operation  may be best left to a profesional.

I would always recommend seals on all the gudes. The valves stems are not designed to require lube on the Ks or Fs, and if you leave the seals off you're inviting smoking, (like mine    )  All the Ks and Fs do fine with ex seals. Only the late Fs have the guide problem which is not an oiling problem but a design angle problem. My understanding is that the aftermarket bronze guides solve that problem.

[CB750F2]

Thanks for your reply. The recutting of the valve seats will be done by a pro. My question about the the valve guide seals was in relation to the exhaust side only. Pat

[mick7504]

G'day Pat

Ron is right on the money with what he said. 
The job is best done by a professional.

Something to think about is one of Big Jays (APE) F2 Cylinder Heads. http://cbrzone.com/sohc.html
You couldn't wrong with one of these on a stock engine.
S/Steel Valves, Serdi Valve Job, Bronze Guides etc.
It would tidy the top end up nicely.

As a guide, I had a guy here in Oz do some porting and assembly work for me a while ago.
He is top shelf at what he does, but with me supplying the material, (Guides, Valves, Seals etc) that job set me back well in excess of 800 bucks for labour and machining alone.

Mick

[MCRider]

Thanks for your reply. The recutting of the valve seats will be done by a pro. My question about the the valve guide seals was in relation to the exhaust side only. Pat

Great! had to get that out of the way.

As to the seals, I did know you asked about ex side, that's where my comments meant to lay. Although i said "all the guides", the intakes are assumed.  Honda went sans ex seals on the K0 only. Ex seals on all other models. Must not have liked the smoking on the K0.  I suggest using the ex seals. If you're like me, you won't appreciate the smoking on a newly refurbed engine. Oiling the valve stems is not an issue.

[mick7504]

Thanks for your reply. The recutting of the valve seats will be done by a pro. My question about the the valve guide seals was in relation to the exhaust side only. Pat

Great! had to get that out of the way.

As to the seals, I did know you asked about ex side, that's where my comments meant to lay. Although i said "all the guides", the intakes are assumed.  Honda went sans ex seals on the K0 only. Ex seals on all other models. Must not have liked the smoking on the K0.  I suggest using the ex seals. If you're like me, you won't appreciate the smoking on a newly refurbed engine. Oiling the valve stems is not an issue.

It will settle down Ron, with some work and a bit of load on the newly installed components.
I once called one of my rebuilds "Nancy" because it continually complained but eventually became a good reliable unit.
Wrong thread I know, but love that video clip. 

[CB750F2]

Thanks Mick and Ron. I never had any intention of fitting the new guides myself - I do not have the equipment or the experience to the job. However, I intend to do all the "hack work" - remove old guides and cleanup the combustion chambers and ports where there is a lot of carbon. The pro can then fit the new guides, cut the new seats, check the head for warpage and machine if necessary. In my original post there are three questions:-
1            Can I drive out the guides from the top after removing the circlips?
2            Are the new guides oversize? Some of the old guides appear to be moving in the head.
3            Is it a good idea to fit valve stem seals on the exhaust guides?
Mick, I have been given an estimate of $200.00 to install the guides and cut the seats and $400.00 too rebore to 836. Does that price sound reasonable? Thanks, Pat

[mick7504]

Hi Pat

Yes the guides can be removed from the top once the circlips are taken off.
The new bronze guides from APE are not oversize.
Maybe you could mike up the old guides once they are removed to see if there is any variation in their diameters to try and find out why some of the old guides appear to be moving.

A light surfacing on the head is also a good idea.
I personally like to have the top of the cylinder block very lightly decked as well to get everything billiard table flat.

Yes, fit valve stem seals to the exhaust side as well.

The pricing that you have been given is in the ball park for this type of work.
Check with your machinist that he is aware that he will be boring from 61mm to 65mm and that the base of the sleeves will require chamfering afterwards to give the new rings a lead in when the new pistons are installed.
I would expect all of this to be done for the price that you have been given.

Mick

[CB750F2]

Thanks Mick. I spoke to the machinist last week and he knows what I want and will do what I want. Mark has given me the required piston to bore clearance. However, I am a bit concerned about the exhaust valve guide movement. I can see evidence of oil seeping down betwen the exhaust guide and head. I think that, before I do anything else, I should take the head in to my man for a discussion. Last night I tried a light tapping with a drift on a couple of the guides. They moved quite easily. I don't think any heat would be required to remove them.
I also intend getting the cylinders lightly decked. So I think that we are "on the same page".
Mick, this is not the bike I rode in the rally. Same model different bike.
Pat

[bryanj]

The guides should be a tight fit in the head and require a decent whck to move them so it might be they have been out before and made the head oversize.

Also if you don't run valve stem seals you will burn oil at between 150 & 300 Miles per pint Or to put it another way chocking smoke after overun

[MRieck]

 
 Kibblewhite makes oversize guides but the guide bores have to be round. Yours are more than likely egg shaped secondary to rocking when the valve is opened and closed. In that case the bores need to be reamed. If you go this route mark on the head somewhere that the guides have oversized OD's i.e. guides + .006

[CB750F2]

Thanks Bryan and Mike. I now have a pretty good idea what I need to do. Tomorrow I will take the head to the engine rebuilder and then go from there. Thanks again to all for their input. Pat

[74750k4]

Thanks for your reply. The recutting of the valve seats will be done by a pro. My question about the the valve guide seals was in relation to the exhaust side only. Pat

Great! had to get that out of the way.

As to the seals, I did know you asked about ex side, that's where my comments meant to lay. Although i said "all the guides", the intakes are assumed.  Honda went sans ex seals on the K0 only. Ex seals on all other models. Must not have liked the smoking on the K0.  I suggest using the ex seals. If you're like me, you won't appreciate the smoking on a newly refurbed engine. Oiling the valve stems is not an issue.

I recently purchased a 71K engine. The guides are steel/iron, and the exhaust side has no provision for mounting a seal, (rounded at tip). Maybe I have a K0 head here, or did that type guide usage, extend into some early K1 heads as well??? The guides seem tight (no slop) around the stem, with the face off the seat. So is it a worthwhile effort to tear into this thing just to put guides with seal mounts on the exhausts? Is it going to smoke if I don't?

Thanks!!!

[CB750F2]

That is a tough question. I am not experienced in that area so I will let others answer. Mine had seals, 0.006" wear and a build up of oily carbon under the valve head. There was also evidence of movement and oil leakage between the guide and the head so in my case it was an easy decision. If your motor had been running without blowing smoke and not using oil I would probably leave well alone. If you have a frame kit fitted the decision would be easier. Pat

[bryanj]

K2 onwards had seals, before that didn't