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

[HondaMan]

My usual machine shop, which is reliable and excellent and has been for 20+ years doing my engines, ran into troubles with Yamiya's CB750 valve guides. Specifically 2 things:
1. They are oversize by 0.0022". This doesn't show on their literature nor instructions. So, the head has to be bored to accept them, which means then you have non-stock holes.
2. The chips turn magnetic while boring - SO magnetic that the coolant flow could not dislodge nor wash them away, and the holes in many of them are now chewed up and oversize.

While the former is a matter of choice, or necessity when repairing a damaged head, the latter is inexcusable, IMHO. Neither Honda's last cast-iron guides nor the former Stellite iron guides ever did anything like this, and I've done a LOT of 750 guides myself...

[M 750K6]

Thanks for the heads up.

Good suppliers are like gold in this 'hobby'. I have Yamiya on my 'decent' supplier list, so that's concerning. Have you let them know / what response?

👍

[rotortiller]

If the head is aluminum and you are boring that material out to fit the guides how are the aluminum chips made magnetic? Valve guides are supposed to have an interference fit no?

[bryanj]

I think Mark is talking about the fact you have to ream the bore of the guide after fitting to get the proper size

[69cb750]

1. They are oversize by 0.0022". This doesn't show on their literature nor instructions. So, the had has to be bored to accept them, which means then you have non-stock holes.

Id to small or od to large?
I have reamed many valve guides through the years for valve stem clearance, Honda guides usually the right size id and od.
Let Yamiya know.

[rotortiller]

I think Mark is talking about the fact you have to ream the bore of the guide after fitting to get the proper size

Then English must not be your first language, other than calling a head a had i. BTW it is normal to ream the tight hole inside the new guides to achieve the correct  clearance to the valve stem. Mark has stated he had to bore the boss in the head that the guide fits into and somehow aluminum chips from this process have become magnetic.

[rotortiller]

The guides are from Yamiya are machined externally, so why not machine those to size provided the fit is incorrect rather than screw up the head? One or two thou for the interference fit into the head seems fine for other bikes. I have machined aluminum often and have never turned it into a magnet. Sounds like a cluster-f.

[bryanj]

I am english and know that Mark said the head was bored but it aint possible to make alluminimum magnetic

[MauiK3]

Hmmmm, I get the meaning
I don't think a guide to valve fit can be set before guide installation in the head.
Hence Mark's problem
I'll venture a guess Yamiya will take notice, up to this point I've always gotten a good response from them.

[pjlogue]

My usual machine shop, which is reliable and excellent and has been for 20+ years doing my engines, ran into troubles with Yamiya's CB750 valve guides. Specifically 2 things:
1. They are oversize by 0.0022". This doesn't show on their literature nor instructions. So, the had has to be bored to accept them, which means then you have non-stock holes.
2. The chips turn magnetic while boring - SO magnetic that the coolant flow could not dislodge nor wash them away, and the holes in many of them are now chewed up and oversize.

Wile the former is a matter of choice, or necessity when repairing a damaged head, the latter is inexcusable, IMHO. Neither Honda's last cast-iron guides nor the former Stellite iron guides ever did anything like this, and I've done a LOT of 750 guides myself...

Mark,

Please forgive me for perhaps misunderstanding your post.  Magnetization of Iron during machining/drilling, etc. is common.  The way I read your post was that the contaminants from marching caused  damage to the head/ and or the valve guides.  A thorough cleaning of all components should have removed the metal.  Did you mean to imply that the magnetic adherence of the cut metal caused  damage to the (as yet to be machined) part of the guide?  I would think the magnetically adhered chips would not cause a problem with the cutting tool.  The force needed to cut iron/steel is much greater than wiping off a magnetic piece of steel. 

I am confused about this.  I need to replace valve guides in a 750 head.  Something I have not done before.  I want to make sure my I's are dotted and T's crossed before I undertake this project. 

-P.

-P.

[MRieck]

I have installed over 15 sets of the Yamiya CB750 guides with no problems at all. I move the c clip groove up .080" to eliminate the keepers/seal problem seen with high lift cams. I also taper the guides on a lathe for improved flow. I have not had any issues with magnetization.
 The guides are honed for final size and my machinist has never...I repeat never had a problem. In fact he has said they are very nice quality with the bores very concentric and hone nicely leaving an excellent finish. I have used them for Kibblewhite and Vesrah valves.....valve stem OD's can vary a few tenths or so.
 I have only used 1 type of guide that needed the ID bored and they were aftermarket for the 400F and those were bored prior to installation to ensure straightness. I think the ID was .005 or so to small.
 The Yamiya guides are the best iron guide I've found out there. The OD is very consistent and the finish is the best I've seen for an iron guide. I don't think they deserve a bad rap at all.

[MRieck]

 Also....guide honing is infinitely better than reaming. You use a Serdi....or any other carbide pilot....and hone to achieve final fit. The ID finish is superior and you can get the exact fit you want.

[HondaMan]

Thanks for the heads up.

Good suppliers are like gold in this 'hobby'. I have Yamiya on my 'decent' supplier list, so that's concerning. Have you let them know / what response?

👍

Not yet: I just found out yesterday - but I will: they need to know, too.

[HondaMan]

If the head is aluminum and you are boring that material out to fit the guides how are the aluminum chips made magnetic? Valve guides are supposed to have an interference fit no?

It's the grinding chips for the ID boring of the iron guides that went magnetic. Aluminum doesn't do that.
Yamiya's guides (at least this set) are 0.0022" to 0.0024" oversize on their outside, which means the head must be bored in order for them to fit in. Normal interference fit is 0.0002"-0.0006" 0.0012"-0.0016", with 0.0008" 0.0018" upper limit, which has always been Honda's fit-up for these (any many other) heads. These guides are "oversize" guides, and their ID is also 0.0024" undersize, requiring reaming after installation. To get to the minimum clearance of 0.0008" 0.0018" for the intake this means boring them about 0.0030", and for the exhausts another 0.0004"-0.0008" on top of that. That's quite a bit of boring just to install guides!

[HondaMan]

This particular shop does heads and cylinders every day, and in 2006 I 'taught' them how to do Honda heads in my particular special way (i.e., always minimum ID clearances). They are a great shop and have been for a long, long time: the owner is just 11 years younger than me and never "screws" anyone, either: I've seen them close the shop for a week once when a new employee did something wrong to an engine, and the entire shop stopped what they were doing and rebuilt the whole thing themselves (dragster stuff) to go on to win the NHRA class meet that Fall - that's how straight they are.

I've seen the ID of the guides: one of the intake side actually has grooves cut in it from the chips getting caught (despite coolant flow) during the sizing bore, and that was against the flow of coolant to boot. He bores cast iron to (-0.0002") to (-0.0004") less than final size and then either runs a honing tool to final, or bore to final, depending on how things look. It was the last one bored: by then the boring bit was also magnetized enough to hold up a 4x10mm screw, as a test (he also has a demagnetizer, which works real well on keys, too!). That has never happened before that he can remember, and they do heads all day long. He has only done one other 750 head for me with iron guides (I normally use bronze) some years ago, and it was fine, with close tolerances and no problems in bore finish. This whole thing is most unusual.

I'll contact Yamiya and report what they think about it.

[MRieck]

If the OD is a bit to large put the guides in a lathe and use some sandpaper to reduce the OD. It doesn't take long to pull a thou off. I would never rely on 2 to 4 tenths or even .0008 interference for a guide especially one the doesn't have an oring around the guide to stop oil from leaking past the guide. I go with .0015 to .002 which is pretty standard for aluminum heads. I use a ball gauge to measure the bore as factory Honda bores can be different from hole to hole but that being said I haven't had to reduce the OD on any Yamiya guide.....they all have driven in perfectly. Driving the guides in should be similar to driving a 10 penny nail into a seasoned oak plank.
 An aside...Suzuki and some other manufactures supply replacement guides that DO require reaming to fit. Also....no more bronze guides as they do not last.....I don't care how much nickel they add. It's just about impossible to get Ampco-45 too.....you need to literally buy a ton of it. I've seen them sacked out in under 5,000 miles of street use. Keith Byers....who knew metals better than me or most anybody....and I had this conversation many, many times.
 I've done a few guides in my life too. The last time I went to recycle metal I had 5 gallon bucket filled with them.

[scottly]

Driving the guides in should be similar to driving a 10 penny nail into a seasoned oak plank.
 

That was my experience with VW heads, after heating the head up in the oven first.

[MRieck]

Driving the guides in should be similar to driving a 10 penny nail into a seasoned oak plank.
 

That was my experience with VW heads, after heating the head up in the oven first.

Right

[bryanj]

The old Triumph 650 bronze guides lasted longer than the cast ones but heads were actually machined differently as well as different guide material, also they didnt rev as high!

[HondaMan]

Honda's OEM cast iron guides, found in all of the 750s but the ones built before 3/72 and the 1 year of the 750F0 (those all had Stellite guides, phenomenal stuff, that...) don't last long with unleaded gas. I haven't seen one in spec after 10k miles in decades. The ones that went through the years of MTBE are deeply pitted even inside the guides, and the exhaust versions of those look like they went thru a sandstorm on their outsides and like someone wrapped emery paper around the valve stems and ran it on the insides.

I currently have over 25k miles (more like 28k) on my APE bronze guides in my 750K2, and when I had to pull the head off due to serious hail damage a while back (welded on new fins!) the valve guides had no detectable wear. I don't know what bronze APE uses, but they are my go-to guides for these heads and have been for decades. They sell a lot of them: once a long time ago the owner emailed and said these were the first bike guides they made for sale, in the last century (I used them then, too).

[MRieck]

Honda's OEM cast iron guides, found in all of the 750s but the ones built before 3/72 and the 1 year of the 750F0 (those all had Stellite guides, phenomenal stuff, that...) don't last long with unleaded gas. I haven't seen one in spec after 10k miles in decades. The ones that went through the years of MTBE are deeply pitted even inside the guides, and the exhaust versions of those look like they went thru a sandstorm on their outsides and like someone wrapped emery paper around the valve stems and ran it on the insides.

I currently have over 25k miles (more like 28k) on my APE bronze guides in my 750K2, and when I had to pull the head off due to serious hail damage a while back (welded on new fins!) the valve guides had no detectable wear. I don't know what bronze APE uses, but they are my go-to guides for these heads and have been for decades. They sell a lot of them: once a long time ago the owner emailed and said these were the first bike guides they made for sale, in the last century (I used them then, too).

Stock cam/springs I assume or maybe springs with a bit more pressure....not 80lbs on the seat. I have APE bronze guides in my FJ and they are OK...there is a lot of valve angle (which is why the FJ and the DOHC Honda's) were difficult to get a lot of power out of compared to the TSCC Suzuki. Anyway....the FJ and the DOHC Honda have shim/bucket which centers cam load eliminating most side load. The rocker arm set up introduces a lot of side load especially when using heavy spring pressure and high lift cams. You start revving the thing a lot....like road racing...and those bronze guides go bye bye quickly. Doesn't matter if it is Kibblewhite, APE etc.
 The point of this thread is the Yamiya iron guides. I have had absolutely no problems with ID or OD....I don't think it is fair to bad mouth the product and I hope you can appreciate my candor. I also recommend heating the head and drive the guides in...  .0015 to .002 fit works. If you write to Yamiya I have a feeling they are going to tell you they have had no complaints about the parts and I would believe them....they strike me as a very honest business based on my many transactions. Try Kibblewhite iron guides if you are unhappy but you'll have to get them from CycleX and you'll find a similiar OD.

[HondaMan]

Honda's OEM cast iron guides, found in all of the 750s but the ones built before 3/72 and the 1 year of the 750F0 (those all had Stellite guides, phenomenal stuff, that...) don't last long with unleaded gas. I haven't seen one in spec after 10k miles in decades. The ones that went through the years of MTBE are deeply pitted even inside the guides, and the exhaust versions of those look like they went thru a sandstorm on their outsides and like someone wrapped emery paper around the valve stems and ran it on the insides.

I currently have over 25k miles (more like 28k) on my APE bronze guides in my 750K2, and when I had to pull the head off due to serious hail damage a while back (welded on new fins!) the valve guides had no detectable wear. I don't know what bronze APE uses, but they are my go-to guides for these heads and have been for decades. They sell a lot of them: once a long time ago the owner emailed and said these were the first bike guides they made for sale, in the last century (I used them then, too).

Stock cam/springs I assume or maybe springs with a bit more pressure....not 80lbs on the seat. I have APE bronze guides in my FJ and they are OK...there is a lot of valve angle (which is why the FJ and the DOHC Honda's) were difficult to get a lot of power out of compared to the TSCC Suzuki. Anyway....the FJ and the DOHC Honda have shim/bucket which centers cam load eliminating most side load. The rocker arm set up introduces a lot of side load especially when using heavy spring pressure and high lift cams. You start revving the thing a lot....like road racing...and those bronze guides go bye bye quickly. Doesn't matter if it is Kibblewhite, APE etc.
 The point of this thread is the Yamiya iron guides. I have had absolutely no problems with ID or OD....I don't think it is fair to bad mouth the product and I hope you can appreciate my candor. I also recommend heating the head and drive the guides in...  .0015 to .002 fit works. If you write to Yamiya I have a feeling they are going to tell you they have had no complaints about the parts and I would believe them....they strike me as a very honest business based on my many transactions. Try Kibblewhite iron guides if you are unhappy but you'll have to get them from CycleX and you'll find a similiar OD.

I think, in the end, this will be the [engine] owner's call: he provided the Yamiya guides as his desired parts in this case. I would like to know Yamiya's take, though, on why they would magnetize in the boring process: I've worked with many cast iron guides for years, too, and never saw this happen before. Granted, most of the ones I installed were done by hand (like the Honda manual teaches!) with hand reamers, etc., and at most, an electric drill running the reamer once the skin came off the hands. But, I have never seen chips sticking to the guides on any I've done before? I've milled quite a few cast iron parts before (used to work in a machine shop myself) and haven't seen it happen, either. That's what has me puzzled.

[seanbarney41]

I have seen drill bits go magnetic many times...drilling bolt holes in mild steel by hand.  Generally not a problem with something that imprecise, but you certainly notice when it happens.  If the magnetism becomes a problem, seems like something got too hot and one needs to re-think coolant situation, drill speed, bit sharpness, cutting pressure, and/or amount of material being removed and then go to the supply cabinet and get a new bit.

[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.

[rotortiller]

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.  Reaming guides is typical while boring is not and the OP does not use the term ream. Reaming by hand would likely not cause magnetic debris. A professional would size the guide OD rather than tamper with the head unless there was damage to be repaired. The valve guide manufacturer recommends "This product doesn't easily get deformed like genuine parts when striking it in. We recommend assembly at a specialty store with solid knowledge and skills". After screwing up the first guide, the light should have come on and another technique applied, rather than driving gyproc screws into wall studs. I would have been happy with .002" (0.05mm) interference fit (oversized) which is common with various bikes of this vintage.

Generally a cloudy situation in general. I would try a hand reamer before passing judgement and laying blame. I think if you asked the valve guide manufacturer what they expect for a interference fit (oversized) might also be wise, they are designed by them for that specific engine after all. If it were my cylinder head and valve guides and I knew it was screwed up, I would be pissed off, especially if it was expected to stay that way after parting with installation cash.   Here is the general installation process but with non ferrous guides.