Valve guide to valve clearances tightening up

Hello,

I'm going through my engine after part of a carburetor slide went through the left cylinder. When I took out the left exhaust valve, it was quite tight in the guide, I had to drive it out with a brass drift. I thought maybe it was bent, but the right one was pretty much the same. Has anyone ever seen this? I'm running Black Diamond exhaust valves and bronze valve guides on the exhaust. What should the clearance be? I can't remember what the vendor I bought them from told me, it was several years ago.

-Eric

Were they carboned up, at all ?

Sticky valves because of oil carboning up in the guides used to be a problem, decades ago really.
Aircraft oils adopted "ashless" spec to the additives, to completely avoid this problem.
Most engines use fairly large clearances (relatively) in the valve guides, to avoid this possibility.

Did the guides come with the black diamond valves as a set.
If they were supplied quite separately, maybe they weren't to the same clearance spec, ever.. ??

Are you sure it's the valve stem to valve guide clearance? When I take the valves ( Black Diamond) out of mine I find that the collet grooves have galled a little and make it tight to get out of the guide.

I just take a bit of emery and clean up the top of the valve where the collet grooves are before I drop the valve out of the guide.

Retainer has probably burred the stem when removing the collets

pommie john said:

Are you sure it's the valve stem to valve guide clearance? When I take the valves ( Black Diamond) out of mine I find that the collet grooves have galled a little and make it tight to get out of the guide.

I just take a bit of emery and clean up the top of the valve where the collet grooves are before I drop the valve out of the guide.

Click to expand...

+1

pommie john said:

Are you sure it's the valve stem to valve guide clearance? When I take the valves ( Black Diamond) out of mine I find that the collet grooves have galled a little and make it tight to get out of the guide.

I just take a bit of emery and clean up the top of the valve where the collet grooves are before I drop the valve out of the guide.

Click to expand...

+1

A bit of judicious stoning before attempting removal avoids this

pommie john said:

Are you sure it's the valve stem to valve guide clearance? When I take the valves ( Black Diamond) out of mine I find that the collet grooves have galled a little and make it tight to get out of the guide.

I just take a bit of emery and clean up the top of the valve where the collet grooves are before I drop the valve out of the guide.

Click to expand...

I'll look at that, hopefully, I haven't screwed up the guides. This is the first time I've ever seen this, first time I've ever run Black Diamond valves, are they more prone to it? From memory, I'm pretty sure the valves were tight before the collet area reached the guide. I didn't notice much carbon on the valves, none really on the stems.

-Eric

Hi all,

I just looked at one of the exhaust valves again, didn't really see any deposits on it, didn't see any burrs on it either. It sounds like if the burrs occurred it would be the top edge of the groove would be mashed outward slightly by the collets? The top edge of the collet groove felt smooth when I rubbed it from top to bottom, but sharp (as I would expect) when I rubbed it from bottom to top.

I did notice something interesting. When I inserted the valve stem into the top of the valve guide it went in an inch or more with no resistance. When tried inserted it from the bottom, it felt stiff almost immediately. So I think I have some deposits on the inside of the guides. I guess I can see if my machine shop can ream them out again. Are there any cheapo Harbor Freight-type reamers I could try to do this myself with? What should the recommended clearance be for bronze guides and Black Diamond exhaust valves? I have cast iron inlet guides. I believe that exhaust valve guides should be looser on the valve stems, since the exhaust valves run much hotter. However, I'd think that bronze guides could be run tighter than iron ones, since bronze has a higher coefficient of thermal expansion than cast iron.

I'm noticing some slight burrs on the edge of the valves, I guess from beating up on the piece of carburetor slide, none really on the seat or seating face of the valve. I'm wondering if I should try to smooth them up, or just get new valves.

-Eric

If the bronze guides are of a high quality modern material like Colsibro or Ampco 45, then they are probably setup with very little clearance, possible 1.5 thou.
These new alloys work at very close tolerance and provide greater support to the valve stem than the old cast iron guides, which required much greater clearances. The alloy guides wear extremely well and can last 100,000 miles in an aircooled engine. In addition seat wear is reduced because the valve lands in the correct location with the tighter guide clearance.
Because of the close tolerance, any little burr on the valve stem will become a problem on removal.

Glen

Do you have a fiberglass gas tank?

Could be the dreaded "honey" from the inside of your gas tank being dissolved by modern fuel.

grandpaul said:

Do you have a fiberglass gas tank?

Could be the dreaded "honey" from the inside of your gas tank being dissolved by modern fuel.

Click to expand...

When the bike ate the carburetor slide I was running a steel roadster tank, but I ran a fiberglass interstate tank for a while with this cylinder head incarnation, but I didn't see any deposits on the inlet valves or ports as I'd expect if it was from dissolved fiberglass resin.

-Eric

The burr on the collet groove can be very subtle and dressing with a stone usually allows for ease of passage of the stem.

Clearance on an AMPCO45 type guide is set tighter (cold) because the AMPCO coefficient of thermal expansion is closer to that of the cylinder head alloy and greater than the valve stem body.

Cast iron guides hav a thermal coeeficient of expansion closer to that of the steel valve stem so clearances must be set looser than for bronze (AMPCO45) guides.

With such a close fit I would be leary about running a reamer through. I think they have hones that will remove and clean up a bit slower. That's my recommendation. Don't save a buck here; go to (or send to) a reputable service provider.

.

Dances with Shrapnel said:

Clearance on an AMPCO45 type guide is set tighter (cold) because the AMPCO coefficient of thermal expansion is closer to that of the cylinder head alloy and greater than the valve stem body.

Click to expand...

This depends on the type of valve selected. My 1360 heads use Colsibro which has a similar coeffcient of expansion to Ampco 45, both right around 9 x 10 to the minus 6 in/in per degree F. The valves are tuftrided stainless, same thermal coefficient as the guides.
So in theory the tight clearance remains a tight clearance at all engine temps.
Good advice to avoid the reamer,a wet hone is needed on this material.

Glen

Good point there worntorn. Although we can discuss in generalities, the devil is in the details and it all comes down to the specific materials used.

Some examples of thermal coeficients of expansion (all multiplied by 10-6) :

Aluminum 12-13
Copper Beryllium 10
AMPCO45 9
S. Steel 5.5 - 9.6
Steel 7
Cast Iron 6

Thus the greater the coeeficient of expansion of the guide, the tighter (relatively speaking - regardless of what valve material you use) you can/should run it when cold to achieve an acceptable running clearance when hot. Conversely, the greater the coefficient of the valve material, the loser you need to run it cold. You must look at material properties of both the guide and the valve.

So if you have an AMPCO45 guide with a steel valve you have a 1 point spread.
If you run a cast iron guide with a steel valve you have a -1 point spread.

This is one of the reasons I like the copper beryllium as it more closely matches the coefficient of expansion of the aluminum head. It is also tough, durable and has a way superior thermal conductivity than AMCO45, SiBronze, Cast Iron and just about anything out there. Great for exhaust seats also.

If it's some kind of deposit in the bore of the guide , surely a solvent would get rid of it rather than having to get it reamed or honed ?

If its some kind of deposit causing the problems, the clearance needs to be made bigger, to prevent it occuring again.

Reaming bronze guides just smears them around, they need to be correctly honed.

If you had carb bits banging around in the cylinder, I'd look real closely for a bent valve stem. It doesn't take much.
Jaydee

pommie john said:

If it's some kind of deposit in the bore of the guide , surely a solvent would get rid of it rather than having to get it reamed or honed ?

Click to expand...

Does anyone use solvents to clean up carbon deposits, etc? I've always been nervous they would attack the underlying aluminum, bronze, cast iron, etc. I've always scrapped off the carbon with a rounded end of a machinists rule and then polished it up with Simichrome, it's quite tedious.

-Eric

Carbon exposed to boiling water long enough with turn to a greyish dust to wipe off or they have piston varnish coke cleaners to soak in then wipe off w/o harm to the metal.