Topic: Cast iron guides for 5mm valve stems?Fix: back to stock thickness 6.6mm stem valves, cast iron guide

[PeWe]

This head will go back to stiffer 6.6mm  stems.
I'll see which ex guides that will fit the rather wide holes.

I have ordered cheap car cast iron 6.6mm ex guides that hopefully can be made to fit. 50.5 mm long, 12.11mm thick.

CycleX have valves,  guides and spring kit with everything.

I have a stock K1 head in need of new guides so extra guides are welcome.

I'll update with photos when fixed.

[PeWe]

Got the SS valves (34/28mm), springs, retainers and cast iron guides from CycleX. 
Guides will fit fine.
34mm inlet valves  with 6.60mm stems (stock size) for CB750K0-K6 not that common either. The hard chromed SS valves from CycleX will fit the head that earlier had 34mm 5mm stems KPMI valves.  28mm ex. They all will get a 30 degree back cut for smoother flow.

The old ported head soon restored and ready for another engine build.
CycleX super rods, Dynoman JE 67mm (890cc) 12.5:1 pistons for the 24.4cc chambers.
Stock crank. (not lightened this time)
A good looking later trans that will get undercut gears 2-4. I need to remove the final gear and mount it on a K shaft.
All parts in garage except for hardwelded rockers that will match Megacycle 125-20 cam. I save that bill to autumn CycleX has the kit for affordable price.

The final compression test will show which cam to use. If too high with 125-20, possible to use DP315 with "normal" lash around 0.004"-0.006" (0.10-0.15mm).

(My ported K2 head got 197.5-202.5 PSI and ran fine on Shell V-Power).  Upper limit not known, yet.

[johno]

Hi Pewe,
Ive been watching your thread with interest, I love headwork and camshaft chat.
You seem to have a good handle things and your headman seems to know what's good or not. The only tip I would add is whatever guide valve combo you use the the number one chore is to get the valve / cam geometry as close to perfect as you can.
This can be a bit tricky depending on how the valve seats have been cut, ie best use a good valve machine cuts all the seats the same depth and you don't have to adjust each cylinder differently.
then use the valve stem length to get the correct geometry. In a race engine this becomes critical as the side loads will eat the small stemmed valves for breakfast. Usually its the valve springs being too weak that cause valve heads to drop but on our cb 750 cam / head arrangements I believe its more likely the Valve / cam geometry is the cause in HP engines or race applications. Its my experience that very few engine builders adjust valve / cam geometry on our old Hondas as measuring and cutting the valve stems takes time. Also adjusting the height of the cam bearing towers etc.
So if I was you ( Pewe perfectionist ) I would assemble head and cam on bench using normal valve with light test spring and before you put on rockers and adjust clearances spread some bearing blue onto the valve tip then adjust the clearance if you want and rotate the cam through a full open and close cycle, remove the rocker and have a look at the rub pattern on the valve stem end. The rubbing mark should be equal distance from centre of valve not to favour one side. The options you have to centre the rub mark is, lash caps, cam bearing tower up or down, valve stem length.      Give it a try at least Pewe
That usually makes the difference between a normal engine and a great engine. 
cheers Johno

[PeWe]

Hi Johno,
Thanks for your very good input.
The guy that restore had concerns about the seats that have been cut some times now. So the valve tips might be on the upper side.
Shim the cam holders to compensate would be fine if possible.

The old lash caps on 5mm stemmed valves had a centered wear as I can recall so the geometry might have been within the OK range.

Test with the cams I have in mind can be important.

Lash caps will build more, maybe not possible to cut the tip enough.

Another head use F2 in valves with lash caps that adds height on the shorter F2 valves which is good.
The caps are rather soft, not that hard. Need to be replaced within around 20.000 kms I guess.

I'll know more within a week or 2.

CycleX shiny 34/28 mm valves with hard chromed stems together with their cast iron guides can be a cost effective restore for 5mm stem kit that has worn out upper part of guides too quick for a street bike. 

I ordered an extra set of 34mm valves for future use.

//Per

[PeWe]

Update:
Head back from restore and ready for action!
5mm stem valve kit replaced by CycleX cryo 6.60mm guides, 34/28mm ss valves and their spring kit.
They needed some shimming to reach 90lbs pressure according to the mechanic.

I have 2 threads to fix, one old time sert that creeping up, an old heli coil that start to come up too, cam stud on 4.

I like clean ports and chambers!!

CycleX cryo treated iron guides shortened 3mm on the port side to match the previous setup with kibblewhite bronze 5mm guides. 
Assembly can handle  valve lift of 12+ mm which will be enough!

Head had got sunken head nuts. All those areas machined to be true parallel and fit stock (2.3mm) thick 18 mm washers.