To Lap? Or To Grind? That is the Question.

Well, I am putting new valves in my 1999 yz400f (Steel Valves BTW), and I am wondering if I should have a local machine shop grind the valve seats, and then lap them?

Or if I should not have them grind the seats, but only lap them.

Thanks.

With steel valves, you have the option of lapping or not lapping when fitting new, or grinding old valves.

(Excuse me a second)NEVER under ANY circumstances lap a Titanium valve! Ever.

OK, I'm back. If the machinist does a good job with regrinding the seats, there is really no need to lap the valves. If it's done right, there's no harm in it, either, but there is little or no benefit. It is a useful process in cases where the valves are seeping a little during a solvent test, and are not bad enough to need a full regrind, but too flaky to use.

(Excuse me a second)NEVER under ANY circumstances lap a Titanium valve! Ever.

Yup, I know that much...LOL

OK, I'm back. If the machinist does a good job with regrinding the seats, there is really no need to lap the valves. If it's done right, there's no harm in it, either, but there is little or no benefit. It is a useful process in cases where the valves are seeping a little during a solvent test, and are not bad enough to need a full regrind, but too flaky to use.

My valves actually weren't leaking at all with the solvent test. I sprayed brake cleaner in, and it actually presently surprised me. :thumbsup:

So should I just lap them?

Yup, I know that much...LOL

My valves actually weren't leaking at all with the solvent test. I sprayed brake cleaner in, and it actually presently surprised me. :thumbsup:

So should I just lap them?

um for what i no brake cleaner drys up fast, use alcohol ( and no not the kind your drink)

So should I just lap them?

That's what I would do if it were mine.

um for what i no brake cleaner drys up fast, use alcohol ( and no not the kind your drink)

If you spray enough in there, it makes a pool, and doesn't dry super fast like normal.

BTW, thanks Gray.

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