Topic: Valve stem to guide clearance question

[Jay B]

I eBay'ed a head for my 350f to experiment on, doing some home porting work. It looks like it came from a good running bike judging from the deposits in the chambers. I've only had a chance to remove one set of valves and here's what I found. The intake guide seems to be in great shape. No side to side clearance to be felt, the stem runs smooth through the guide, and the valve won't drop out by itself, even with the seal removed. The exhaust, OTOH, has a little side to side play (not much, but perceptible) and it will drop out on its own. Also runs through the guide very smoothly. It stands to reason it would need a little more clearance than the intake since it runs much hotter and probably expands more. Does this sound right, or am I looking at some guide work while I'm messing with it?

[tomkimberly]

You should really mic the valve stems and use pin gages to check the valve guides. The probable reason the valve will not fall out is it has a few burrs where the keeps were. Be careful removing them as you can damage the guides. Use a small diamond file of hone stone to remove the burrs before trying to remove the valves.

Tom

[MRieck]

You should really mic the valve stems and use pin gages to check the valve guides. The probable reason the valve will not fall out is it has a few burrs where the keeps were. Be careful removing them as you can damage the guides. Use a small diamond file of hone stone to remove the burrs before trying to remove the valves.

Tom

Yes...deburr the tops. I think you mean a ball gauge...not to be snooty.

[tomkimberly]

No, I meant pin gages. I would never do that with mine 

Just "borrow" a set from work (you do have a receiving Inspection Department right)?

If not, new unused drill bits will work just as good, just use the chuck end, not the twist end.

Tom

[Jinxracing]

If not, new unused drill bits will work just as good, just use the chuck end, not the twist end.

If you're using drill bits as hole gauges, it's a good idea to mic the drill bit first to confirm actual size...sometimes they're a few thou undersize down towards the chuck end. 

[Jay B]

I've got the rest of the valves out. I didn't find any burrs on any of the stems. I was unclear in my first post. When I said the valves wouldn't just drop out of there, it wasn't like there was any metal to metal contact, ie burrs, but rather the surface tension of the oil would hold them. With almost no effort they slide right out, right up to the end. The first exhaust valve I removed was the worst. There was side to side cleareance, but almost imperceptible.

[Hockers Choppers]

What kind of tolerance is TOO tight? I'm working on my cb750 (again) Last guy reamed out the guides to .261, way too loose( smokes at high rpms ) , book said .260, I've been told .259 and hone. If it goes in and moves is it not too tight? Where do you get the right size of guide hone?

[HondaMan]

I eBay'ed a head for my 350f to experiment on, doing some home porting work. It looks like it came from a good running bike judging from the deposits in the chambers. I've only had a chance to remove one set of valves and here's what I found. The intake guide seems to be in great shape. No side to side clearance to be felt, the stem runs smooth through the guide, and the valve won't drop out by itself, even with the seal removed. The exhaust, OTOH, has a little side to side play (not much, but perceptible) and it will drop out on its own. Also runs through the guide very smoothly. It stands to reason it would need a little more clearance than the intake since it runs much hotter and probably expands more. Does this sound right, or am I looking at some guide work while I'm messing with it?

Jay: Honda's original methods were to pull the valve out about .300" (i.e., cam lift distance), then measure the X and Y slack. You'll find the guides to be oval, which is the wear pattern. Try to measure across the chamber opening ("X" direction) and then toward the piston and toward the head ("Y" direction) with a dial gauge. More than .003" in one direction is pretty worn.
For reference: my 750 was at .0022" up-and-down ("Y") and .0015" ("X") last summer, at 112,000+ miles. Wasn't burning oil. I replaced the valves with some out of a 27,000 mile motor with good results, less than .0012" worst case.

When they wear, the valve stops rotating, which lets crud build up on the faces. Then they typically start leaking, then burn.

[MRieck]

What kind of tolerance is TOO tight? I'm working on my cb750 (again) Last guy reamed out the guides to .261, way too loose( smokes at high rpms ) , book said .260, I've been told .259 and hone. If it goes in and moves is it not too tight? Where do you get the right size of guide hone?

Jesse, the intake guide is honed to .001 to .0012 clearance. The exhaust .0015 to .0017. This is for aftermarket bronze guides. My machinist hones them on a Sunnen horizontal hone with the appropriate small bore hone(s). I have seen vertical hones which are basically a hand held drill with a couple of U joints that allow the hone to "float".  Don't ream those aftermarket guides...hone them. It leaves a better (oil retentive) finish on the ID as well.

[Hockers Choppers]

Thanks Mike,
None of the shops around here have a hone that small. One does have a .260 reamer. The exhaust seems fine but the intakes are tight.

[MRieck]

Thanks Mike,
None of the shops around here have a hone that small. One does have a .260 reamer. The exhaust seems fine but the intakes are tight.

They should be able to get a ball hone in the right diameter....that will work well with the bronze guides Jesse.

[Hockers Choppers]

I did find a 6.4mm and a 7mm ball hone on ebay for cheap. They aren't really the right size so I didn't get them. Where is a good place to buy one the right size? 6.6mm? .260? Should I tell the machine shop with the .260 reamer to hold off? My intake valves measure .259 so it should be OK?

[MRieck]

I did find a 6.4mm and a 7mm ball hone on ebay for cheap. They aren't really the right size so I didn't get them. Where is a good place to buy one the right size? 6.6mm? .260? Should I tell the machine shop with the .260 reamer to hold off? My intake valves measure .259 so it should be OK?

I believe the OD on the 6.4 ball hone is .275 with a grit of 120...it would work IMO. Jesse...if the reamer is a thou over and it is straight and put in a Serdi it should be OK. A 6.4 brush hone would leave a nice surface and wouldn't remove material after the reamer. I just hate reamers.

[HondaMan]

What kind of tolerance is TOO tight? I'm working on my cb750 (again) Last guy reamed out the guides to .261, way too loose( smokes at high rpms ) , book said .260, I've been told .259 and hone. If it goes in and moves is it not too tight? Where do you get the right size of guide hone?

Jesse, the intake guide is honed to .001 to .0012 clearance. The exhaust .0015 to .0017. This is for aftermarket bronze guides. My machinist hones them on a Sunnen horizontal hone with the appropriate small bore hone(s). I have seen vertical hones which are basically a hand held drill with a couple of U joints that allow the hone to "float".  Don't ream those aftermarket guides...hone them. It leaves a better (oil retentive) finish on the ID as well.

After market bronze? (Drool...)
Where do you find those?

[Tom Stark]

What kind of tolerance is TOO tight? I'm working on my cb750 (again) Last guy reamed out the guides to .261, way too loose( smokes at high rpms ) , book said .260, I've been told .259 and hone. If it goes in and moves is it not too tight? Where do you get the right size of guide hone?

If you want to actually hone the guide to size, you need to get a sunnen valve guide hone.  I paid around $500 for mine more than a few years ago.  This is a ridged hone, with a single stone that is pressure fed out.  You can controll the pressure.  The advantage this has over a ball hone is that it will, (or make that CAN if used by experienced hands), make the guide straight and round.  If the guide has a "loose spot" in the center, the ball hone will be making that larger as it works on the tighter parts top and bottom.  With a ridged hone, it will not touch the loose spots untill the tight spots are even with it. 
So far as how loose is too loose, I can tell by the wiggle.  Hard to give instruction on that by email.  Also, I do not pull the valve out a bunch, I keep it closer to the seat.  The valve spends most of the time near the seat, PLUS you want to measure the stem to guide clearance, if you pull the valve way out, (like full lift), this multiplies the clearance.  Depending on the guide length, stem length, distance from bottom of guide to valve head, this could pile up to make the clearance "felt" to be more than double the actual clearance.  Put the valves in bone dry, with bone dry and very clean guides.  There should be some slight movement.  If it feels too loose, put oil on the stem and try again.  If it feels ok then, you are ok.  Again, I have machined thousands of heads, my ok and your ok could be VERY different.  If you are really unsure of yourself, get some go, no go gauges, or make your own from gauge pins.  Gauge pins cost around $2 each and are a cheap alternative to the go no go gauges. 
Tom

[Hockers Choppers]

I ended up taking it to the machine shop and he was just going to ream the top 1/8 to get it to go. He had it all set up in the machine and was running a ton of oil to it and the reamer wouldn't touch it. He had one for steel and needed one for bronze, got one and cut my guides. They look great and he got them to spec. ( .001 intake and .0015 exhaust ) I have the head  together and just waiting for some free time to get the rest of the engine assembled. The guy cut the guides, ground the valves, seats, and lapped valves in, deglazed cylinders, and asked me if $80 was too much!?!!?? He even had to buy a $50 reamer!?! I fell like building another engine just to give him more business! I would if I had another liver

Free time? What the hell is that??

[Big Jay]

After market bronze? (Drool...)
Where do you find those?

http://cbrzone.com/valves.html

[Big Jay]

What kind of tolerance is TOO tight? I'm working on my cb750 (again) Last guy reamed out the guides to .261, way too loose( smokes at high rpms ) , book said .260, I've been told .259 and hone. If it goes in and moves is it not too tight? Where do you get the right size of guide hone?

If you want to actually hone the guide to size, you need to get a sunnen valve guide hone.  I paid around $500 for mine more than a few years ago.  This is a ridged hone, with a single stone that is pressure fed out.  You can controll the pressure.  The advantage this has over a ball hone is that it will, (or make that CAN if used by experienced hands), make the guide straight and round.  If the guide has a "loose spot" in the center, the ball hone will be making that larger as it works on the tighter parts top and bottom.  With a ridged hone, it will not touch the loose spots untill the tight spots are even with it. 
So far as how loose is too loose, I can tell by the wiggle.  Hard to give instruction on that by email.  Also, I do not pull the valve out a bunch, I keep it closer to the seat.  The valve spends most of the time near the seat, PLUS you want to measure the stem to guide clearance, if you pull the valve way out, (like full lift), this multiplies the clearance.  Depending on the guide length, stem length, distance from bottom of guide to valve head, this could pile up to make the clearance "felt" to be more than double the actual clearance.  Put the valves in bone dry, with bone dry and very clean guides.  There should be some slight movement.  If it feels too loose, put oil on the stem and try again.  If it feels ok then, you are ok.  Again, I have machined thousands of heads, my ok and your ok could be VERY different.  If you are really unsure of yourself, get some go, no go gauges, or make your own from gauge pins.  Gauge pins cost around $2 each and are a cheap alternative to the go no go gauges. 
Tom

http://www.goodson.com/store/template/product_detail.php?IID=1838&&

[Hockers Choppers]

WELL!!! I got he bike running on Sunday. Rode it to work and back today ( 30 miles ) STILL FUKKING SMOKES!! I'M READY TO BASH MY FACE INTO A BEER!!!!!!!!!!!!!!! I guess .001 is still too much clearance?? intake ports are wet with oil!!

[Wheelhorse77]

WELL!!! I got he bike running on Sunday. Rode it to work and back today ( 30 miles ) STILL FUKKING SMOKES!! I'M READY TO BASH MY FACE INTO A BEER!!!!!!!!!!!!!!! I guess .001 is still too much clearance?? intake ports are wet with oil!!

Have you discovered what the problem is yet?

[Tom Stark]

What kind of tolerance is TOO tight? I'm working on my cb750 (again) Last guy reamed out the guides to .261, way too loose( smokes at high rpms ) , book said .260, I've been told .259 and hone. If it goes in and moves is it not too tight? Where do you get the right size of guide hone?

If you want to actually hone the guide to size, you need to get a sunnen valve guide hone.  I paid around $500 for mine more than a few years ago.  This is a ridged hone, with a single stone that is pressure fed out.  You can controll the pressure.  The advantage this has over a ball hone is that it will, (or make that CAN if used by experienced hands), make the guide straight and round.  If the guide has a "loose spot" in the center, the ball hone will be making that larger as it works on the tighter parts top and bottom.  With a ridged hone, it will not touch the loose spots untill the tight spots are even with it. 
So far as how loose is too loose, I can tell by the wiggle.  Hard to give instruction on that by email.  Also, I do not pull the valve out a bunch, I keep it closer to the seat.  The valve spends most of the time near the seat, PLUS you want to measure the stem to guide clearance, if you pull the valve way out, (like full lift), this multiplies the clearance.  Depending on the guide length, stem length, distance from bottom of guide to valve head, this could pile up to make the clearance "felt" to be more than double the actual clearance.  Put the valves in bone dry, with bone dry and very clean guides.  There should be some slight movement.  If it feels too loose, put oil on the stem and try again.  If it feels ok then, you are ok.  Again, I have machined thousands of heads, my ok and your ok could be VERY different.  If you are really unsure of yourself, get some go, no go gauges, or make your own from gauge pins.  Gauge pins cost around $2 each and are a cheap alternative to the go no go gauges. 
Tom

http://www.goodson.com/store/template/product_detail.php?IID=1838&&

OK "Big Jay" where the hell were you 20 years ago when I bought mine!
That's the tool.  Of course, MINE came with a metal box and 4 or 5 mandrells and stones.   
tom

[MRieck]

What kind of tolerance is TOO tight? I'm working on my cb750 (again) Last guy reamed out the guides to .261, way too loose( smokes at high rpms ) , book said .260, I've been told .259 and hone. If it goes in and moves is it not too tight? Where do you get the right size of guide hone?

If you want to actually hone the guide to size, you need to get a sunnen valve guide hone.  I paid around $500 for mine more than a few years ago.  This is a ridged hone, with a single stone that is pressure fed out.  You can controll the pressure.  The advantage this has over a ball hone is that it will, (or make that CAN if used by experienced hands), make the guide straight and round.  If the guide has a "loose spot" in the center, the ball hone will be making that larger as it works on the tighter parts top and bottom.  With a ridged hone, it will not touch the loose spots untill the tight spots are even with it. 
So far as how loose is too loose, I can tell by the wiggle.  Hard to give instruction on that by email.  Also, I do not pull the valve out a bunch, I keep it closer to the seat.  The valve spends most of the time near the seat, PLUS you want to measure the stem to guide clearance, if you pull the valve way out, (like full lift), this multiplies the clearance.  Depending on the guide length, stem length, distance from bottom of guide to valve head, this could pile up to make the clearance "felt" to be more than double the actual clearance.  Put the valves in bone dry, with bone dry and very clean guides.  There should be some slight movement.  If it feels too loose, put oil on the stem and try again.  If it feels ok then, you are ok.  Again, I have machined thousands of heads, my ok and your ok could be VERY different.  If you are really unsure of yourself, get some go, no go gauges, or make your own from gauge pins.  Gauge pins cost around $2 each and are a cheap alternative to the go no go gauges. 
Tom

http://www.goodson.com/store/template/product_detail.php?IID=1838&&

OK "Big Jay" where the hell were you 20 years ago when I bought mine!
That's the tool.  Of course, MINE came with a metal box and 4 or 5 mandrells and stones.   
tom

Jay was at APE 20 years ago but at the Burbank location.

[HondaMan]

STILL SMOKES!! I guess .001 is still too much clearance?? intake ports are wet with oil!!

No, that's a good clearance. We need to look elsewhere.
What plugs are you using? What jets? Are the pipes straight, or baffled? And, what is the timing?

[Hockers Choppers]

mic'd measurement, not with the dial indicater like the manual shows. The intake ports were soaked with oil! has to be coming from the guides.

[Clyde]

Are your valve seals OK?
Regds Clyde