Topic: cb750F3 guides and valves - cast or bronze, chrome or nitrided

[garyS-NJ]

My '78 cb750F3 has worn exhaust valve guides (I know, I know...) and I thought the popular modification to address this design issue was to install the kibblewhite extra long cast iron guides... So while looking for the big valves (mine are a little tired) and guides, one seller told me that the premature exhaust guide wear on F2/F3 was because Honda used a long guide which they discontinued and recommended his shorter Ampco45 guide.  He said the longer guide isn't able to dissipate heat like a shorter guide and the Ampco guide is better for long life (and works wonderfully with his stainless and nitride valves...).

I can't understand how a guide with more surface area could retain more heat and never heard that heat was the cause of this F2/F3 premature wear problem.  Granted that a bronze guide would conduct heat better than iron...  but then why didn't kibblewhite make the long guides out of ampco45? 

I thought that cast iron guides were more for long life and bronze was more for high rpms (when oil starves and only the bronze would survive).  Is this true or what?  I mean why are the stock guides cast iron and most aftermarket guides made of bronze..  And what about AMPCO45 vs C63000?

And I read one head shop tech guy saying that Bronze against stainless steel will always gaul and may eventually seize and so he didn't like relying on the black nitriding coating on a stainless valve..  He likes hard chrome valve stems (and I think still uses AMPCO45 guides).  And what are my stock valves made of and finished with??  I cleaned them up soaking in simple green and then a wire wheel but their still not polished..  Assuming the dimpling on stem tips is minimal and I want to use the stock valves, could I hurt the faces or backs with the wire wheel (trying to stay off the seating area).  Should I scrape the crud off and wire wheel the faces/backs and polish?  can I do some of this in the head so as to clean the chambers but protect the valve seat surface///

so in short, which guides to address the F2/F3 problem and then what's the best available valve (is that my stock valve?)

[seanbarney41]

good questions that I would like to know the answer to...have heard that APE has the best parts for sorting f2/3 valve train issues?

[Old Scrambler]

+1 about good questions.................BUT...........do not SCRAPE with a metal object   A soft wire brush (I use brass) is good.

I tend to agree with you regarding the coatings but would NOT use chrome with iron guides.

To add to the questions............Where are the guides longer? Raising the top-end will move the seal closer to the retainer and may hit if you use a performance cam. Added metal to the bottom is NOT where you want it.  Getting the exhaust-gas out is important

I'm still in grade-school about metals and their compatibility.............so I looked to the racing-industry for info about my F2 build for the salt-flats......http://forums.sohc4.net/index.php?topic=135473.0........but not much concern about thousands of miles down the road.

[bwaller]

I read lately Mike Rieck recommends the Kibblewhite cast iron guides for that head. Maybe do a search for more info. 

[edwardmorris]

I read lately Mike Rieck recommends the Kibblewhite cast iron guides for that head. Maybe do a search for more info.

Yep, just had those installed on my K2 by Mike. I asked him for the best ones that will last a looooooooooong time and that's what he recommended.

[Dunk]

Not sure on the guides especially for F heads. Logically I'd imagine the longer the guide the more heat would be pulled out of the valve and dissipated to the head. Not sure on materials but I'd heard of issues with coated valves in K heads losing the coating fairly quickly and sometimes being fine or other times marring the guides. I would also think longer guides (and/or harder guide material) would wear less since there's more supported area and maybe a harder material.

For cleaning crud off valves I use a brass wire wheel in a die grinder. Let them soak in cleaner for a bit to soften it up. I don't wire wheel the sealing edge or the stem, but go to town on the areas crud builds up. Nylon brush/rag/scrub/etc. to get anything on the stem where it goes through the guide.

[garyS-NJ]

Thanks Yes, I know Mike knows those heads so the long cast guides must help.  The long cast guides are 49.5mm long vs the stock exhaust 47.3mm cast iron guide which is 5% increased length.  On the Guides, Manley for Harleys says bronze only for racing and cast for street and state their chrome stems or nitride valves are both compatible with either their cast iron or bronze guides.  They said their nitride valves have a harder surface than chrome (and finish can't chip like chrome) and have less friction and recommend nitride finish for severe duty like turbo and heavy diesel applications.  IDK where the guide is longer but I'm sure the long kibblewhite cast guides are designed to work with a stock F2/3 cam.  Jerry Branch flow testing for sohc cb750's found the valve and guide introduce minimal restriction as the flow is restricted by the carbs.  they found max flow increases produced by mikuni 30 or 32mm carbs and porting intakes (and said exhaust ports are not a restricting factor).
Scrambler - what's your issue with chrome stems?
APE doesn't offer anything special for F2/3 exhaust guide issue but uses stainless valves (nitride? IDK) and bronze guides in the F2/3 head rebuilds.
Dynoman sells AmPCO45 or C63000 guides.  Cycle-X recommends the Cast guides for F2/3 with Nitride over stainless valves but also sells AMPCO45 guides.
So I'm leaning towards the Kibblewhite long cast iron guides and may well use my stock valves if they are OK..  APE sells an Iconel Stainless valves for $40 (IDK who makes them) and Dynoman sells a nitride stainless valve for $21 made by Kibblewhite. 
My valves cleaned pretty good with Simple green soak and steel wire wheel but some still have some baked on crud on the faces.  scrape and wire wheel does take it off but Scrambler, are these stock valves coated with anything?  (I assumed it was a solid unfinished stainless valve./

[garyS-NJ]

FYI here's the old Jerry Branch article.  really makes me think about getting my heads ported or finding a set of those 30mm mikuni carbs..  http://draftcycleworks.blogspot.com/2010/09/porting-honda-head.html

[garyS-NJ]

one key blurb from Jerry in case you don't feel like opening or reading his article/.. the stock cb750 can only use a fast lift long duration cam (not high lift) unless the head is ported (or you get a set of mikuni smooth bore carbs).  The F motors have just that.

"The first bit of information gained from the stock configuration test was that the Honda 750 head reaches maximum flow at a valve lift of only .250. At the .250 lift point, air flow has risen from zero to 54.8-CFM (cubic feet per minute). Going all the way to .450 lift only increased the flow to 58.7-CFM, indicating that the stock Honda Four engine requires a cam with a long duration, which will open the valve quickly and hold it open at moderate lift (about .300-inches) for an extended period of time to allow complete filling of the cylinder. High lift is not needed and cannot be used effectively until the port shape is improved to a point where the engine will flow much larger amounts of air at high lifts."

[garyS-NJ]

regarding my valves, I still have them soaking in simple green (couldn't start the head work anyway) and they have some stubborn carbon on the exhaust valves (mostly faces but some on the back side between seat area and stem.)  Old Scrambler said don't scrape the valves with anything.  is that because the OEM valves have a stellite coating on the faces and backs across the seat area?  I'd imagine a steel wire wheel or scraping across black nitride wouldn't be good and IDK about stellite.  Does anyone know the material/finish of the OEM valves>?

And Scrambler, why not the hard chrome finish stems with the cast iron valves?  Seems many folks using black nitride finish on bronze guides and probably cast guides too but I've heard a couple stories with the black nitride coming off (I'm guessing with the cast guides..  supposedly black nitride provides a smoother and harder surface than hard chrome but there could be other issues.  right now I'm leaning towards the long cast iron guides and if my valves are NG then I want to be ready to order the right thing..

[Bailgang]

I got my 750 F2 together earlier this spring and have been riding it all summer with the cycleX nitrided valves and kibblewhite bronze guides and the bike runs fantastic however anything was better than what it had before. The original exhaust guides were so sloppy I didn't need a dial indicator to know they were shot and all the valves were severely indented at the top of the stems. The original valves could've been salvaged by grinding the top of the stems to remove the indents and lash caps put in place but I opted for the cycleX valves which of course by the time I got them that's when I started reading concerns about the nitride coating coming off but I rolled the dice and installed them anyhow.

Unfortunately I can't give you any useful data in regards to wear of the bronze guides or the nitride coating coming off the valves mainly because as long as the bike continues to run well I see no reason to take it apart just to find out. I'm not trying to be a smart a.. I'm just not taking it apart again unless I have to, besides even if everything was still pristine I've only put maybe 5k miles on it this summer and I wouldn't consider that long term data.

[Old Scrambler]

You can use a high-speed wire-wheel to clean the valves.........and especially the backs to really shine. After the wire-wheel you could polish the backs with red or black rouge to increase flow characteristics.  What I meant by 'do not scrape' is the result of seeing screwdriver or blade scratches that reduce flow and increase carbon buildup.

Mike has a LOT more experience to comment and rely on...............I chose to use heat-treated copper-bronze guides with proprietary stainless-steel alloy valves in my CBR build.

[garyS-NJ]

oops that was a few intake valves with the hard carbon build up..  I ended up scraping most of it with the side of an allen key.  pics attached.  Maybe Mike will comment here on valves to go with the long cast guides.  The only thing I've found it APE's stainless at $50 each and Dynoman's nitride at $21 each.  Bailgang that's still good data 5000 miles and no problems.  And Scrambler, you used the bronze guides in your F2 build or a later model CBR.  How many miles now and what clearance did you run?  AND BTW, I haven't read anything about nitride coatings failing but two folks have mentioned it.  Was it isolated to a batch of valves or vender or application>>??  can you guys paste links>

[DWS]

Need to follow this too, probably need to do mine also.

[garyS-NJ]

wow DWS that looks clean.  Mine had the same seat and I think handlebars when I got it.

[DWS]

Thanks been working on it all summer, any bolt i took off i polished, which was most of them.
the inside of the engine is next i guess.
i love the handle bars when cuisine long rides.
everything has been rebuilt except the motor.

[Bankerdanny]

I am always amazed when I see F bikes with K/Q seats and ape hangers. Why buy a SuperSport and then try and convert it to a cruiser?

[Old Scrambler]

My bad.............CBR is for Classic Bonneville Racer.............some of the build data is under that title on the High Performance page. BTW......brake-cleaner does wonders on valves.

[MRieck]

 I have mixed all types of valves and guides and never had problems with the guide grabbing the valves. The galling issues I have seen are more related to lean running conditions. Guide ID is the most important part.
 Heavy valves, big seat pressure and large valve angles beat up guides. Iron guides are tougher. My machine shop only uses iron guides in Harleys (which meet the 3 criteria I just stated).
 I would check the F2 valve faces very carefully. When the guide wears a lot the valve is bouncing all over the seat and it is no longer concentric. You should not grind the face of the OEM valves.

[DWS]

One good reason is that i bought it new in 78! played, raced, wheeled, even turn my foot pig to the inside of the engine guard so i would not hit it in corners and raised hell and now its time to (cruise) don't want to buy another bike.

[garyS-NJ]

good points Mike.  so only iron guides in the Harleys and on the F2/3's you like the cycle-X cast iron guides better than the Bronze guides?  I run my F3 maybe a little hard with some high cruising speeds (85mph probably gets 7000rpm) and probably too much around 90-95 and plenty of runs to the top around 115 (top is 115 or 120 but I don't look at the speedo too much at those speeds nor do I believe it).  I've heard only the bronze will stay slippery at the high RPM's (does that mean 10000 rpms or 8000?).  I was hoping to get some F2/3 owners who ride hard and have some miles on their bikes to chime in to say what worked.  My bike had 35K miles on it before this teardown and this might be the first..and the exhaust guides had some wear but the seat area on the valves look concentric.  maybe what I'm hearing is the motors will last 35k miles with cast guides if they are ridden nicely and less than that with bronze guides if they are ridden nicely but I know I run her a little hard and want the guide that will be best for that riding.  some folks are saying bronze.  and is the C6300 better than ampco45?  and my intake guides seemed nice so I was thinking leave them alone.