Valve to Guide Clearance

[dln383]

EQ spec head for imca 360 motor that was sold as an assembled bolt on head. I was checking guide clearance and cannot slide the valve in when using a .002 feeler gage strip around the valve stem on the exhaust valve. Guide clearance appears to be .001 on both the intake and exhaust using a snap gage. These of course are cast iron guides and had Teflon positive seals on both the int and exh. Any opinions on guide clearance for this application and should I be getting in touch with the folks that sold me these ready to run heads. Thanks

[machine shop tom]

Using a feeler gauge strip to measure valve stem-to-guide clearance would be problematic, to say the least. A split-ball gauge, at the minimum, is needed, if not a dedicated inside bore gauge.

What I find that works well is a tapered valve seat grinding pilot. I put a line of marker on the valve guide portion, where the pilot goes from straight to tapered. I put the pilot into the guide (chamber or port end) until there is the slightest resistance, then spin it a turn or two. Measure the pilot at the point the marker is rubbed off and compare that with the valve stem. The difference is the guide clearance. To check for a tapered guide, do the same at the top (spring side) of the guide. I've been using this method, along with a rigid guide hone, to get very accurate and consistent results when sizing guides. No more banana-shaped guides from using reamers...............

tom

[Speedbump]

Oh, God! Not the bananas again.

[engineguyBill]

The PC style Teflon seals do an excellent job of controlling oil to the guides. Because of this, you will want to run valve guide clearances on the high side of the recommendation for your engine, otherwise you will run into stem galling and possibly seized valves when using these seals.

[cadamzak]

I Have built quite a few Wissota Midwest mod engines that allow you to run the same "EQ" spec head. And I cannot stress enough to you, to have all of those guides checked for size and honed, or just re-sleeve them with a bronze liner and re-size before you assemble the heads. your going to have probably 2-6 guides per head that are undersize or not even strait. I have seen it on every set i have dealt with. Also another thing your going to want to do is open up the pushrod holes, because there is also not enough clearance for the cam im sure you will have installed. These heads are a great improvement from a stock head but they need a lot of work before they can be assembled. I also wouldnt even recomend running a positive seal on the exhaust side, especially if you are running a very expensive valve. have the exhaust guide clearanced to .0015-.0018 and you will have plenty of lubrication and no seizing problems. it will also be a lot less wear on that stem and guide with no seal.

[machine shop tom]

Oh, God! Not the bananas again.

Heh, heh..........................

[dln383]

I'm not sure why I would not be able to get a fairly good idea of what the stem to guide clearance would be by sliding a piece of 1/4 inch by 4 or 5 inch strip of .002 feeler gauge along side the valve stem into the guide to double check the clearance. Anyone else use this method?

[machine shop tom]

I'm not sure why I would not be able to get a fairly good idea of what the stem to guide clearance would be by sliding a piece of 1/4 inch by 4 or 5 inch strip of .002 feeler gauge along side the valve stem into the guide to double check the clearance. Anyone else use this method?

It's all in the geometry. The feeler strip would have to be contoured so only the closest point between the valve stem and guide would make contact. If you used round strips (wires?) of known diameter you would have accurate results. But wires .0015"to .0030" thick would be pretty fragile...........................


tom

[Brian W]

I use a Sunnen P-310 Valve Guide Gage Set to measure stem to guide clearance. And a Sunnen diamond hone to size. I have did a bunch of the EQ spec heads and usually run around .001 on intake and .0013 on ex. Its a good idea to install k-liners right from the start...