Topic: cb750 Valve Guide and valve seats questions.

[ntm1974]

I am rebuilding a 77 cb750k engine.  The intake valves and guides are in spec but the exhaust guides are way out of spec.  I know I need new guides but was sticker shocked when I got quoted the price from cycle X.  I'm sure they do good work but I can not justify/afford that kind of expense ($325+shipping both ways not including parts.)  I haven't been able to find a local shop to do the work so I am going to try to do it myself.  I've read a number of threads on the topic but still have a few questions:

1.  If I replaced the valve guides and valves, does a new seat need cut in the head or can I grind it (using stones from Goodson as described in hondaman's book?)  The current seat is in decent shape but I wasn't sure if it would be possible to have the new guide in straight enough to get away with just a light grind.

2.  What size valve guide driver do I need?

3.  Can I bypass the entire valve guide issue but buying an oversized diameter valve stem and then reaming the existing valves guides appropriately?

I have a 76 engine that is probably going to need some work as well so I don't mind some investment in tools and ultimately want to do the job right.

Thanks for any advice.

[bryanj]

Its only the 77 and 78 750's that wear out the guides badly.

Once fitted the guides need reaming to fit the valve stems and its an odd size and the seats will need cutting as the guides never go in exactly the same.

Talk to Mike Reik on this board and he will do a superb job including a gas flow, may cost a few bucks BUT it will be 100% right when it comes back

[Graydude]

How do we get in touch with Mike?  His name does not come up on a member search.

[HondaMan]

Mike's forum name is MRieck. You can't get a better valve job.

I will be getting back just such a head as this tomorrow, but with all 8 guides replaced. Then I am taking another F2 head in for just exhaust guides, so I could let you know what this local shop charges. Replacing guides always requires cutting new seats: in my book I was outlining the simpler parts of the process that can be done by hand, such as cutting a fresh seat if the guide is good: this is needed when the face of a valve gets pits from carbon buildup, and is (or at least WAS) a common in-shop repair in the 1970s-80s era. Replacing guides requires careful alignment for the boring of the guide to fit an existing seat, otherwise it requires a full new seat be cut so they are concentric. It can be tricky for the uninitiated, with hand tools like Goodson's equipment.

Generally, I recommend only hand-cutting new seats on good guides. That's what I hoped to portray in the book.

[ntm1974]

Mike's forum name is MRieck. You can't get a better valve job.

I will be getting back just such a head as this tomorrow, but with all 8 guides replaced. Then I am taking another F2 head in for just exhaust guides, so I could let you know what this local shop charges. Replacing guides always requires cutting new seats: in my book I was outlining the simpler parts of the process that can be done by hand, such as cutting a fresh seat if the guide is good: this is needed when the face of a valve gets pits from carbon buildup, and is (or at least WAS) a common in-shop repair in the 1970s-80s era. Replacing guides requires careful alignment for the boring of the guide to fit an existing seat, otherwise it requires a full new seat be cut so they are concentric. It can be tricky for the uninitiated, with hand tools like Goodson's equipment.

Generally, I recommend only hand-cutting new seats on good guides. That's what I hoped to portray in the book.

Mark,

Thanks for the reply.

My misunderstanding has more to do with my lack of experience than any shortcoming in your book.  The books has has been extremely helpfull in this process, exspecially for a complete newbie like me.

[HondaMan]

I struck out at the machine shop until next week. Drat...some local bike shop got in ahead of mine.

[Simpson]

I too was following the book lately while going through the cylinder head. I came to a questionable valve seat and decided to send it to Mrieck.
My exhaust guides seemed a tiny bit worn also. 

Mark, what valves do you recommend for replacement?
-Honda Original
-Kibblewhite
-Cycle X
-Other

[lucky]

The valve seats when original from Honda were cut using a hand operated tool that fit in the valve guide. It was 1.5 turns to recut the seat. the seat on some Honda models has 3 different angles on it for different harmonics at different rpms.

I would save up (not get in a hurry) and let cycle-X do the work.
Cycle X will do an excellent job and not ruin your head.
If you do it with limited knowledge, or let some car machinist do it it, could be butchered.

[HondaMan]

I too was following the book lately while going through the cylinder head. I came to a questionable valve seat and decided to send it to Mrieck.
My exhaust guides seemed a tiny bit worn also. 

Mark, what valves do you recommend for replacement?
-Honda Original
-Kibblewhite
-Cycle X
-Other

If you're a purist snob like me: Honda guides.
They are becoming hard to find, though, and REAL expensive. I like the non-seal types of the K0-K2 engines on the exhaust side, because they last and last and last, and will rev higher with no seal drag.

Next: Kibblewhite. Also expensive. You must select either inlet or exhaust side guides from them.
Next: API, from Big Jay. These are nice bronze guides, low friction, should last a long time, and are reasonably priced. I've done several head with them. I thnk these have undersized holes, which lets them be used either for inlet or exhaust, with one part number. That's good, but may cost a bit more if the shop who reams the guides is running their costs (to you) by the passes through the guides to finished size: some do.

I have not had any experience yet with the CycleX guides. I have a head here from someone who sent it to CycleX, and am assembling the engine for him. That's as close as I have come to this product.

Locally, the shop I use (with a Serdi machine) charges me about $200 to install a set of the API (Big Jay) guides and cut matching seats, and touch-grind the valve to match. These engines run well in both stock bores and 836 size, some having 3 seasons on them now. Before that, I used mostly Honda guides.

[74750k4]

Someone told me don't touch the new valve faces, they are coated... especially lapping. CycleX sells Nitride coated valves. Not sure if that includes the valve face though. So is this BS to ignore, or what!!??

[74750k4]

From the Kibblewhite site FAQ...


Should I face my new KPMI valves, (Black Diamond®, White Diamond® or Tensilite®)?

KPMI has designed all but specific titanium valve applications to be faced and or serviced. KPMI strives for quality and durability when it comes to designing any valve. That being said, it should be noted that for titanium applications that are supplied by KPMI with coated faces, KPMI recommends not facing these valves. The special coatings on the face of these valves will enhance the durability of the valve face.

[HondaMan]

Someone told me don't touch the new valve faces, they are coated... especially lapping. CycleX sells Nitride coated valves. Not sure if that includes the valve face though. So is this BS to ignore, or what!!??

I generally use the $10 variety of replacement valves from places like PartsNmore or CB750supply (among others). They are common metals, and lap in well. Often, though, the OEM valves you have will be fine after they are refaced. All but 4 of the 36+ I have done since January have come out fine with this treatment, at $4 per valve face. A few were bent in an engine that was mis-assembled, so it received the $10 valves, all 8. They are Made In Japan valves, probably a generic size from either a car engine or another bike somewhere: Honda seldom used their parts once.

(Example: Honda boat engines used the oil sump screen from the CB750, same part number, even. Much cheaper at Boats.com, too!).

[74750k4]

Hey...

That's VERY good info. Expensive lesson. Too bad I already popped for the CycleX Superflow valves. The ones that are there already, look pretty decent. The exh guides seem a bit sloppy though, (392 K8 head) I was quoted $475.00 to cut the seats, and install my new Ampco 45 guides (. They called it a "valve job", maybe a con job? Seems a bit steep, even if they do have a Serdi. Still shopping that...

Thanks HondaMan!!!

[HondaMan]

Hey...

That's VERY good info. Expensive lesson. Too bad I already popped for the CycleX Superflow valves. The ones that are there already, look pretty decent. The exh guides seem a bit sloppy though, (392 K8 head) I was quoted $475.00 to cut the seats, and install my new Ampco 45 guides (. They called it a "valve job", maybe a con job? Seems a bit steep, even if they do have a Serdi. Still shopping that...

Thanks HondaMan!!!

I have no doubt that Ken's Superflow valves will do just that: I don't often build big, high-output engines that require that kind of tech, though. I'm just an old guy who likes 750 grease under my fingernails.