Valve lapping procedure

slatgrille

slatgrille

Senior Member
Got my valves refaced and just received my new guides. Ready to lap the seats, but need to know proper sequence. Are they lapped BEFORE the guides are assembled with the valves, or do I have to insert them, do the work and then remove them again? Seems like a PIA to press them in, do the work, then out to clean each port of the used compound. Yes, these are original style 'mushroom' valves.

OR...do I put the assembly together (minus the spring and keeper), then clean up the port before buttoning up each valve unit?

How have you guys done it? Thanks again!

Craig
 
slatgrille said:
Got my valves refaced and just received my new guides. Ready to lap the seats, but need to know proper sequence. Are they lapped BEFORE the guides are assembled with the valves, or do I have to insert them, do the work and then remove them again? Seems like a PIA to press them in, do the work, then out to clean each port of the used compound. Yes, these are original style 'mushroom' valves.

OR...do I put the assembly together (minus the spring and keeper), then clean up the port before buttoning up each valve unit?

How have you guys done it? Thanks again!

Craig
Click to expand...
Craig - Place valve in its spot, then insert the two piece guide from underneath. Be sure to push both pieces completely up, they should hold without the springs and keepers. (Some folks pull up sharply on the valve to seat the guides, but I don’t like that - too easy to scar the mushroom, the botttom of the guide, or bend a valve). Lap in, then push out the guides, remove the valve, and clean up your lapping compound from both the valve and the seat. Inspect your pattern. Repeat as necessary. I wipe my valve and the guides clean, then put a bit of oil in the center of both guide halves before pushing them in for lapping. The key, obviously, is to remove all traces of the lapping compound except when you are actually lapping.

If your two piece valves are too easy to install and won’t hold without the spring then you have a problem. Will likely need to bore the valve guide hole to the next larger size and install oversized guides.

You don’t make mention of refacing the seats. If you haven’t burned a valve you may get by without regrinding the bevel of the seat. You’ll have to inspect the lapping pattern to be sure you are hitting correctly.
 
Have the seats been refaced with a match angle on the valves?

Lapping is generally very manual, old school rebuilding technology best saved for Briggs and Stratton engines that need a light refresh.
 
No burned valves, or pitting on the seats and they're clean. So I DO need to insert guides, lap, remove guides to clean, then reassemble...kind of thought so, but wanted to check. Thank you. I like some old school technology, especially when I'm not set up with expensive equipment...lol. I have a valve grinder, but no seat grinding tool.

Craig
 
You can buy a set of seat cutting tools online for not much money. These have carbide cutters to cut the seats. There should be 60, 45, and 30 degree cutters. The combination is used to get the part of the seat that meets the valve in the center of the valve seat and narrower.

The lapping is used to clean up any non concentricity between the valve and the guide. You should just lap until a uniform gray area is on the valve and seat, and no more.

You may be able to rent or borrow a set of seat cutting tools.
 
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