Topic: Guides on CB750 F2 head: bronze alloy or stock?

[mazingerzeca]

Hello all.
Due to some problems on my CB750 F2 head (oil leaks through stud holes and 4 helicoiled plug holes), I've bought another F2 head. On the first one I installed Dynoman bronze guides, and given that it leaked, I didn't put too many km on it, so the guides should be usable.
I've checked the second head (the one I've just bought) guides, and by moving the valves on it, it seems to have not big wear on them.
My question is: given the guide wear problems on F2 heads (that made me change the guides on the first head), which ones should be more resistant to wear, the stock ones or the Bronze alloy ones?
Thank you.

[mazingerzeca]

I knew that this topic would bring a big controversy...

[simon#42]

my f2 had exhaust valve wear when i bought it last year , as it had only done 16,000 miles i didnt want to replace the guides with the original honda items . in the end i decided to change the valves to some 5mm stem kibblewhite one piece valves and bronze guides . had the engine out last week to install an 836 kit and after 11.000 miles there was no wear at all , i know its a bit early to say if this is a cure but ive got my fingers crossed !

[MRieck]

my f2 had exhaust valve wear when i bought it last year , as it had only done 16,000 miles i didnt want to replace the guides with the original honda items . in the end i decided to change the valves to some 5mm stem kibblewhite one piece valves and bronze guides . had the engine out last week to install an 836 kit and after 11.000 miles there was no wear at all , i know its a bit early to say if this is a cure but ive got my fingers crossed !

The lighter valve makes a very big difference in regard to wear. Not a cheap solution but it will work. You must be using the 32mm intake valve on the exhaust side....interesting idea.

[Big Jay]

http://cbrzone.com/sohc.html

[simon#42]

hi mrieck , yes that was exactly the logic i was using [ time will tell if it works ] also lighter valves dont need big strong springs to control them and this should give the cam chain an easier life . the plan was to use inlet valves in the exhaust side but the shape of the valve was different , more tulip shaped if you get what i mean . in the end we just rang them up and they supplied the correct size exhaust valves , had the inlets .5mm larger than standard as well  . as you say not cheap but when you consider the quality of the product i dont think they were to expensive at all

[mazingerzeca]

But, which guides will last for a longer time? The dynoman guides or the stock ones? I don't know how many kilometers the head has, but the valves I have (which are new) seem to be on the stock guides as tight as they are on the new Dynoman bronze guides. I don't know which material the stock ones are, but it seems harder than bronze. Stainless steel? When I washed the head, the intake guides got flash rust, but not the exhaust ones.
Maybe to be on the safe side, I should use the Dynoman guides, but I don't know if they are more durable or just that they are better for race use, but less durable...

[MRieck]

But, which guides will last for a longer time? The dynoman guides or the stock ones? I don't know how many kilometers the head has, but the valves I have (which are new) seem to be on the stock guides as tight as they are on the new Dynoman bronze guides. I don't know which material the stock ones are, but it seems harder than bronze. Stainless steel? When I washed the head, the intake guides got flash rust, but not the exhaust ones.
Maybe to be on the safe side, I should use the Dynoman guides, but I don't know if they are more durable or just that they are better for race use, but less durable...

Neither of them is a 25,000 mile piece IMO. The bronze dissipates heat better which helps and can run a little tighter. The OEM pieces are pretty expensive though I'm sure I have 4 new ones if you are interested.

[mazingerzeca]

Neither of them is a 25,000 mile piece IMO. The bronze dissipates heat better which helps and can run a little tighter. The OEM pieces are pretty expensive though I'm sure I have 4 new ones if you are interested.

Thanks for your help. So, if there is no big difference between them I think I will leave the ones that the head has, which are stock, I think. I've tried the valves on them and they seem to be tight enough, as tight as they are on the new bronze ones. Anyway, I will take them to the machine shop to have them measured.

[Big Jay]

As Mike said, the oem guides are cast iron and do not dissipate head very well. However, if the ones in your head are not worn, it would be a waste to replace them unless you were building a racing engine. If you replace them, you need to do a valve job.

Do the Dynoman guides say APE on them?

Jay

[mazingerzeca]

No, is not engraved APE on them. They are very similar to the ones you posted, the same colour, same shape, bought a year and a half ago.