Bob Evans
Administrator
Preparation of the stock Briggs head is a very straight forward surfacing operation to gain the minimum amount of head volume. Many people will disagree with the exact cutting operation. Some builders will opt for the best flow possible and work to only surface that portion of the head over the cylinder, while others will surface the entire head to minimum specs looking for compression.
The WKA tech rules look for a minimum legal depth on the head in three places. .011 over the cylinder area. .408 in the area next to the plug hole between it and the cylinder area. The last portion is the raised portion over the valves. It has a minimum depth of .300.
This surfacing operation can be performed by any shop that has a mill. I will say that it pretty much impossible to get to the minimum of each spec on a legal head. If you get the areas over the valves and cylinder down close to the minimum the third area will not be that close. Just the way the heads are made. You can once again use your 4 or 6” belt sander in the horizontal position to perform this surfacing. I still do it this way when I’m doing them one at a time due to the set up time required on a mill. The only thing I add to the process when using a sander is to tape the area over the cylinder to prevent the sander from touching this as that will get you tossed in the tech barn. Just go slow and measure often. I like to leave a couple of thousands excess when cutting the head to allow for any carbon build-up that will occur.
If you are dealing with an old head that has been run on gas and has quite a bit of carbon build up, there are several ways to clean it up prior to the surfacing operation. Certainly the easiest method is to sand or bead blast the head to remove the carbon. Most full time builders will do it this way. This procedure is perfectly WKA legal. For the home builder soaking the head in carb cleaner over several nights and then polishing the carbon off using LIGHT strokes with very fine Scotch Brite will work well. The point here is to not scratch the surface, as the tech man will frown on you in a big way. I have also seen oven cleaner used to dissolve the carbon but, BE CAREFUL as most will also dissolve aluminum if left on too long. Check the warning label on the can.. Today it is WKA legal to bead or sand blast the head to clean it.
If you have access to several heads cut them differently around the valve area. Some cut to the minimum and some with lots of material left their. You can also think about angle cutting the head where you cut more on the exhaust side verses the intake. Then try then all on a block attached to a flow bench! Today with the slapper cams beating the intake valve on the head I like to leave the valve end of the head pretty much stock and then surface the other two areas to .002 above minimum specs.
The WKA tech rules look for a minimum legal depth on the head in three places. .011 over the cylinder area. .408 in the area next to the plug hole between it and the cylinder area. The last portion is the raised portion over the valves. It has a minimum depth of .300.
This surfacing operation can be performed by any shop that has a mill. I will say that it pretty much impossible to get to the minimum of each spec on a legal head. If you get the areas over the valves and cylinder down close to the minimum the third area will not be that close. Just the way the heads are made. You can once again use your 4 or 6” belt sander in the horizontal position to perform this surfacing. I still do it this way when I’m doing them one at a time due to the set up time required on a mill. The only thing I add to the process when using a sander is to tape the area over the cylinder to prevent the sander from touching this as that will get you tossed in the tech barn. Just go slow and measure often. I like to leave a couple of thousands excess when cutting the head to allow for any carbon build-up that will occur.
If you are dealing with an old head that has been run on gas and has quite a bit of carbon build up, there are several ways to clean it up prior to the surfacing operation. Certainly the easiest method is to sand or bead blast the head to remove the carbon. Most full time builders will do it this way. This procedure is perfectly WKA legal. For the home builder soaking the head in carb cleaner over several nights and then polishing the carbon off using LIGHT strokes with very fine Scotch Brite will work well. The point here is to not scratch the surface, as the tech man will frown on you in a big way. I have also seen oven cleaner used to dissolve the carbon but, BE CAREFUL as most will also dissolve aluminum if left on too long. Check the warning label on the can.. Today it is WKA legal to bead or sand blast the head to clean it.
If you have access to several heads cut them differently around the valve area. Some cut to the minimum and some with lots of material left their. You can also think about angle cutting the head where you cut more on the exhaust side verses the intake. Then try then all on a block attached to a flow bench! Today with the slapper cams beating the intake valve on the head I like to leave the valve end of the head pretty much stock and then surface the other two areas to .002 above minimum specs.