Topic: Valve guides: something to watch out for...

[HondaMan]

Oversize guides must be needed if a  head has got a few guide replacements?

I have one ported head that got a few stock guides replaced in the 80's,  bronze guides  at another later  modification.
When those where shot I was worried about  getting guides to fit. That after a chat with my local shop mechanic.

Yamiya was out of stock of their guides. CycleX "frozen" guides went in after those were reshaped in the port area.

I ordered Yamiya guides with my last order just for sure.

Per: if you have a micrometer, I'd be interested in finding out what the OD of your new Yamiya guides are? They are said to be oversized, but not as much as some oversized guides are. I didn't measure them in this case, as the machine shop was installing them instead of me.

[HondaMan]

I keep hearing this "boring" process on the valve guides, boring is different from reaming. Boring creates sizeable swarf chips and reaming does not. Honda, Yamaha and Kawasaki supply and recommend hand reamers for the precision job. It is possible that the valve guide manufacturer followed those techniques while designing the guides (using hand reaming). The first post made it seem like the head boring aluminum chips magnetised and caused the issues and we all know that is not possible with aluminum, so boring ferrous metal could actually mean reaming ferrous guides with a machine. 

With the Serdi and Siuox machines, the terms "boring" and "reaming" are often interchanged: either one is the same operation when using reamers though: technically it is reaming. With a stepped reamer bit, it is sometimes referred to as "boring" if more than one step is involved. which is the case here. The reamer used has a pilot diameter 0.0022" smaller than the hole was to start with, followed by a 0.0010" step and then another to reach the size-to-hone, with a hone used for the final pass. But in this case the final pass didn't even happen after the bad holes showed up. It is almost impossible to see the chips in the coolant flow, though, as it passes through a grille into the recycling pump sump, is moving quickly, and full of bubbles.

In this case, I don't need to try to 2nd-guess this shop's work: they are excellent at this job. I have probably done close to 100 heads with them since 2006, after looking back through my letters and shop tickets, and several of them turned out to be cast-iron guides (customer's preference), too. But what stands out here is: the chips (and the guides still, just slightly) are magnetic. That's what is new.

[MRieck]

 When I taper Yamiya guides in the lathe there is no "swarf"....the material that is removed is powder. Same is true for Kibblewhite iron guides....powder residue. It all falls off the guide....nothing sticks secondary to magnetic forces.
 I noticed in that video the OD of the guide is "adjusted" on a lathe with sandpaper....this is what I said earlier. There is no need to enlarge the heads guide bore(s). The only time I've had to increase the head guide ID is if the ID gets screwed up by the original guide dragging something through it during removal. I'll say it one last time....interference fit of .0015 to .002 is standard for aluminum heads. I don't remember seeing any guide OD specs or interference values in the factory CB750 manual (s)....I will look at my manual when in Massachusetts Friday. I'll also look in the many vintage/modern factory manuals I have from Honda, Suzuki, Yamaha and Kawasaki. The only guide spec I ever remember seeing was a deflection value.

[rotortiller]

 MRieck, I agree. Guides are a cheap sacrificial part so if it gets messed up it's minor. Might be difficult to find other branded guides now that fit the larger bores. Lets say for the sake of argument the guides were too hard to reduce the OD and that is why they bored the head bosses out, knowing machining was a problem  should have led to a reaming test prior to the tuckery. I feel bad for the customer as often in these cases they usually are left holding the bag.

[PeWe]

Oversize guides must be needed if a  head has got a few guide replacements?

I have one ported head that got a few stock guides replaced in the 80's,  bronze guides  at another later  modification.
When those where shot I was worried about  getting guides to fit. That after a chat with my local shop mechanic.

Yamiya was out of stock of their guides. CycleX "frozen" guides went in after those were reshaped in the port area.

I ordered Yamiya guides with my last order just for sure.

Per: if you have a micrometer, I'd be interested in finding out what the OD of your new Yamiya guides are? They are said to be oversized, but not as much as some oversized guides are. I didn't measure them in this case, as the machine shop was installing them instead of me.

I have no micrometer to measure the guides.
I have a new set of Honda stock guides too.

I can not find the Yamiya guides. Somewhere in the garage.

Edit:
Found them were they should be.
Package much smaller than I remembered.

[MRieck]

I have 4 sets of Yamiya in Massachusetts Per...just have to remember to bring back one of my 0-1" mics. I have new OEM guides, APE bronze and Kibblewhite to compare too

[scottly]

These bronze guides came with my K1 engine bike when I bought it in 1979. While fixing all the PO's mistakes, like the valves hitting the pistons, I took the head with the guides to the local Honda shop and had them check for bent valves and do whatever was needed. They replaced 3 of the guides, and these were left over.
The OD of the exhaust guides is .4762", and the OD of the single intake guide is .4760".

[HondaMan]

These bronze guides came with my K1 engine bike when I bought it in 1979. While fixing all the PO's mistakes, like the valves hitting the pistons, I took the head with the guides to the local Honda shop and had them check for bent valves and do whatever was needed. They replaced 3 of the guides, and these were left over.
The OD of the exhaust guides is .4762", and the OD of the single intake guide is .4760".

Those numbers are similar to the modern APE guides' numbers, and the fresh set of them I have on hand, not considered oversized. I've never had to size OD on the APE versions, just the ID. I did have to on a set of Dynoman guides, but it also turned out they were oversized guides for much-used head holes, so that made some sense.

[PeWe]

A micrometer followed me home today. An old Swedish brand.

I did not have a 10mm reference bit to calibrate the micrometer with.

It looks ok at 0 though.

The relative sizes are most important for me.

My Yamiya guides are slimmer then my stock Honda also ordered from Yamiya.
Yamiya 12.10-12.11mm  (Ordered late October 2024)
vs
 Honda 12.12mm
(as 2 old used guides my K6 had before)

I also measured plan c if holes for guides are wide. 
- Kibblewhite bronze guides , almost 12.3mm, measured 2. I have 10 in same lenght.

My old ported K6 head had IN 12.07mm and EX12.08mm at last restore.

I searched for head vs guide interferences. Mike's numbers he wrote in his earlier post  good to know.  Absolute min to ensure no oil consumption when hot feels important. I doubt there are any Loctite that survive the temperature

I guess a higher comp and modified engine runs hotter and need a good crimp.

I read somewhere that a 1/250 of the guide hole in head as a general number.

A Norton forum mentioned 0.001"-0.0015". Stock engine.

Bronze guides have the same clearance as iron?
Bronze might expand as aluminium?

Below my measurements.
The micrometer
4+4:Yamiya
2+2 Honda
2 Kibblewhite bronze ooooversize!

[MRieck]

Very comprehensive Per.

[PeWe]

Very comprehensive Per.

Thanks Mike!
I had to know too
I got thoughts about the guides.

I could not find head vs guide interference in CB750 shop manual.

Only the valve stem to guide clearance when wiggling the valve sideways in the guide without springs.

An ok "softness" with thin oil on stem  vs a bad visible "clonkety-clonk" 

The crimp fit for guides and sleeves are important.
Maybe the manual take for granted that those jobs are done by other shops

Most right, service value (replace now)

[HondaMan]

Excellent tabulation, Per, many thanks!
Your Kibblewhite numbers look just like the Kibblewhite guides I have, too. I know these are rated "oversize" by Kibblewhite.

Yamiya said they will contact their manufacturer for comment.

[scottly]

What are the specifications for the valve stem diameters?

[PeWe]

What are the specifications for the valve stem diameters?

Guide inside diameter is written in the CB750 Shop manual.
I attached a fresh photo from my paper copy.



Note! Cast iron head or aluminium head makes a big difference.
Aluminium heads needs thicker guides.

My Yamiya guides are definitely not too thick. Honda's are thicker.
These are made for a used head with guides taken out, not a new head without guides.

My K6 head with a few guide replacements: In where 12.07, Ex 12.08 mm my guides are balancing on the absolute minimum. 12.12 mm OD guides are needed.
In: 0.005mm. (0,001968")
Ex: 0.004mm (0,00157")

Holes measured by my shop mechanic so I knew before order guides.

Here a document I found. It supports Mike's minimum numbers.

The recommendation of 1/250 of guide or hole ends up in 0.0019".
Very, very small difference if this is 1/250 of guide hole in head or guide OD.

**** From attached pdf I found: *****

- Cast iron and bronze valve guides fitted to cast iron cylinder heads require an interference of:
0.025 - 0.038 mm (0.0010” - 0.0015”)

-Cast iron and bronze valve guides fitted to aluminium cylinder heads require an interference of:
0.038 - 0.051 mm (0.0015” - 0.0020”)

It is advisable to heat the entire cylinder head, especially if it is aluminium, to about 150°C before fitting.
********************************

Bronze will expand by heat more than iron, right? Almost as aluminium?
In that case can the interference number be in the lower end.

So,  the  Norton numbers I found on a Norton forum feels sloppy with only 0.0010" as minimum if aluminium head. If cast iron no problem.

One more reason to not overheat the engine if guides OD is relatively slim  ....
Rattle when hot?

The pdf as photo too.

[rotortiller]

PeWe,

The truth is always welcome, thanks kindly for posting it like others did.

rt

[PeWe]

PeWe,

The truth is always welcome, thanks kindly for posting it like others did.

rt

This is one of the good things about this forum.
We all can provide ideas and thoughts with information we can find.

I hope Mike will chime in with statistics of heads with guide replacements. He has done a few by himself.

What about a common size of guide holes ID in head when replacing the first set of guides?

If early vs later heads differ. Something that crossed my mind now

I'll see if I can find an old post about it on this forum. Strange if not

[MRieck]

PeWe,

The truth is always welcome, thanks kindly for posting it like others did.

rt

This is one of the good things about this forum.
We all can provide ideas and thoughts with information we can find.

I hope Mike will chime in with statistics of heads with guide replacements. He has done a few by himself.

What about a common size of guide holes ID in head when replacing the first set of guides?

If early vs later heads differ. Something that crossed my mind now

I'll see if I can find an old post about it on this forum. Strange if not

Of course I didn't bring my mic or ball gauges with me from the new house but I can take a head or 2 with to the new house and compare. I have seen variation in the head ID's on the same head. Maybe tooling was at the end off its life? Anyway...I was talking to Rick Stetson about all of this and he has his opinions. He likes to run about .003 guide /head interference fit. He said absolutely no to .0002 -.0004 and never heard of Honda issuing a .0008" max interference fit. I still don't know where that figure is posted as I have looked at 3 different CB750 manuals as well as the factory 550 and XL250. Nothing in the RC-51 factory manual or VFR etc etc etc. I got sick of looking.
 I would like to know where Mark got those figures because I can't find anything.
 Stetson had just finished a head for me that I picked up today. There was no magnatizing (past or present) or any other shenanigans with the Yamiya guides and he agreed they are a good product. They hone perfectly. He also agreed that reducing the OD of the guide ...if necessary...is better than reaming the head. Also said that replacement OEM Honda guides were oversized on the OD like all the OEM replacement guides I have used. As I mentioned before the only replacement guide I have seen that required reaming the head guide bore was the Suzuki 1100 TSCC heads but I have used Kibblewhite replacement guides which....while slightly OS....fit the stock guide bore perfectly.
 The Kibblewhite catalog list all the specifications for all their guides and valves so if somebody wants to compare go on your internet machine and go to work.

[HondaMan]

Hmmm...I came back to read this whole post and discovered the 'controversy' going on, but didn't understand "why" until i went back to read and correct my tolerance post. It seems I have a balky or errant keyboard on this laptop from time to time that transmutes keysstrokes on the keyboard-row scan (and as you can see right there, doubles keystrokes sometimes): while I have to say that's embarrassing (and also angering at times) I haven't had the time to replace the keyboard (or find one). It's also evident on some of my other posts, sad to say: I went and read half a dozen others and they are (were) full of typos, too.

So, my [computer's] bad and mine for not proofing this, here, sorry for the confusion! (even typing this line, it dropped out the "i" and "o" in "confusion", and made "my [computer's] bad" into "my computer's ad". Grrr... While the computer I used for my book these last 3 months doesn't have this problem, it also has Windows on it, which I detest with everything I can safely say in this forum...this one has Linux, far better...
 

Yeah, 0.0002" is a little too light of a press-fit unless you're pressing glass into wood, then it's appropo...

[scottly]

 The Kibblewhite catalog list all the specifications for all their guides and valves so if somebody wants to compare go on your internet machine and go to work.

Kibblewhite claims the intake valve stem diameter to be .2590", and the exhaust to be .2585", but "6.6mm" for both. Were the stock valves the same?
I did make a quick measurement of one of my bronze exhaust guide's ID with a .200-1.00" inside micrometer (it looks like a tiny monkey-wrench) and came up with .2585", but a more accurate measurement may have read larger? Gauge pins would probably be the most accurate..
As far as the guide holes in the head, if the head was heated properly for both removal and installation, there shouldn't be an issue, just like with cylinder sleeves.   

[PeWe]

This thread has good info for me.
I know which guides to use in my old K1 head with no ex guide seals.
My Yamiya guides. (Which started my interest of this thread)

I have another ported head that has got the guides replaced by a home porting PO that might have been a brutal operation.
Guides still OK when its ports got improvements/corrections,  but can have use of the  thicker Honda guides next time. Head on the shelf, not used so it can take a while

I have asked around about the guide holes.
Answer I got from a guy that has worked with CB750 heads and other heads for decades:

"I would guess that the original nominal measurement is 12.00- 12.015mm.
 
Disassembled 1 time, would guess the hole diameter 12.020 - 12.030mm if the dismantling has gone ok with a shiny hole without metal residues on the dismantled guide.

If it came with material on the guide, then the hole may be a bit conical."

[PeWe]

......
 Anyway...I was talking to Rick Stetson about all of this and he has his opinions. He likes to run about .003 guide /head interference fit.
....

0.003" = 0.0762mm
That must sit tight
No oil to be sucked in at high rev throttle offs via the guides outsides.

I guess he has noticed that a certain size can be mounted without excessive force when head has been in an oven for a while.

My Yamiya guides 12.10 - 12.11 mm

Head might have 12.020 -12.030mm holes if it gets the first guide replacement without problems when taking them out. Old guides are blasted clean in ports and head is really warm.

12.10-12.020=0.08mm
12.10-12.030=0.07mm

12.11-12.020=0.09mm
12.11-12.030=0.08mm

A little bit to grind off.

A head as my old ported K6 head with several guide replacements needs oversized guides. It is also waiting to be used.
I have to do that engine build soon...

- What's next?
A quick and simple port improvement while guides are out?

[HondaMan]

I've found that used heads had to be heated to get the old guides out without tapering the holes so much. This makes it hard to do in winter! The sun here in summer is so strong that it can heat the head to 160 degrees (F) on a summer day, and then i spray some freeze-spray into the guides and knock them out. They usually come right out, then. Freezing the new guides to -15 F in the deep freezer lets them go right back in, too.

In wintertime I take them to the shop: they have a big oven for the heads (and my wife won't let me use hers...).

[HondaMan]

- What's next?
A quick and simple port improvement while guides are out?

That would sure make it faster and simpler: grinding around the guide sides is tricky.
It also lets you see clearly the air path. On the intake side, though, a bit of disturbance helps with street bikes (not raced) in that the turbulence around the valve at lower engine speeds helps prevent the fuel falling out of the air a little bit better. This reduces "wetting" of the intake port surfaces while sitting at stoplights, etc., which improves the sparkplug life in places like Chicago or Los Angeles with their heavy traffic.

[brianc]

I have my F2, sucking oil down the outside of the guides puffing smoke, so I need to sort this. Long story.
I have a set of aftermarket guides but they weren't used as the OD is at least 0.01mm smaller than old OEM guides I have here, they virtually drop in. Not happy. So, my question is can anybody tell me the differences between the K series (Yamiya style) guides and the F2 guides? they have a different part number. Yamiya don't specifically supply F2 bits.
Are they different length, material, circlip position? Finished ID is the same, Valve stem seal is the same part no (xx-300-xx). Could I use Yamiya guides? (as the slight OS would be a good fit in my head (cylinder that is....) Thanks

[MauiK3]

Also, to freeze things to get them smaller
Drop some dry ice in some isopropyl alcohol and wait for it to turn to a light honey thickness, put the guide in and it will really shrink. Don't touch anything, it will give you frostbite.