To Lap or not to Lap ... yup, that's the question - Kawasaki KLR 650 Forum
1987 to 2007 Wrenching & Mods For maintaining, repair or modifications of Generation 1 KLR's. 2007 and earlier.

View Poll Results: lap or no lap
yes 5 83.33%
maybe - depends 1 16.67%
probably not - depends 0 0%
Never - but then what? 0 0%
Multiple Choice Poll. Voters: 6. You may not vote on this poll

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post #1 of 30 Old 02-05-2018, 07:51 PM Thread Starter
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To Lap or not to Lap ... yup, that's the question

About half way through the 685 build, valves are out and clean, head soda blasted clean - waiting on vinton seals ... So while Sherman and I were hanging out, I took a moment to read up on lapping valves in this particular machine. The advice is all over the place from never to light to yes on klr dot net. I have always lightly lapped valves when given the change - kind of a matter-of-course - on a rebuild ...

What does sage wisdom say here ... I'll get a pic of the seat and valve soonest ... but for the theory, let's proceed please.
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post #2 of 30 Old 02-05-2018, 08:16 PM
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A good lap dance, err I mean Valve lap job is a good thing. Do you know what is even better for your KLR cylinder head?

Narrowing the valves seat to near Minimum Specs! It increases the psi of seating spring pressure.

I'll about bet your valves have 2+ mm of contact surface. Maybe as much as 3 mm?

Specs call for .8 - 1.2 mm. That is .032 - .048 inch.

The work hardened surfaces will retain adjustment far longer, because of less seepage from both lapping & narrowing.
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Modify at "YOUR OWN RISK"!

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post #3 of 30 Old 02-05-2018, 08:24 PM
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To do a quick clean-up of the valve face and seat? Sure!

As a substitute for a valve job, when things are marginal and that is what is really called for? NOT!
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post #4 of 30 Old 02-05-2018, 09:40 PM
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Quote:
Originally Posted by pdwestman View Post
A good lap dance, err ...
You owe me a new keyboard. Coffee came out of my nose.

Tom [email protected]

I lit a cigarette and dragged a smoking stand beside the chair. The minutes went by on tiptoe, with their fingers to their lips. -Philip Marlowe

'Why' and 'How' are words so important they cannot be too often used. -Napoleon Bonaparte


Sting like a butterfly.
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post #5 of 30 Old 02-06-2018, 07:26 AM Thread Starter
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Talking sounds great!

Quote:
Originally Posted by pdwestman View Post
A good lap dance, err I mean Valve lap job is a good thing. Do you know what is even better for your KLR cylinder head?

Narrowing the valves seat to near Minimum Specs! It increases the psi of seating spring pressure.

I'll about bet your valves have 2+ mm of contact surface. Maybe as much as 3 mm?

Specs call for .8 - 1.2 mm. That is .032 - .048 inch.

The work hardened surfaces will retain adjustment far longer, because of less seepage from both lapping & narrowing.
ok ... I like the idea and know a small seat is better. 1.6 on the intake and 1.4 on the exhaust ... ya got one of them-there fancy videos on how to make a smaller dance seat to give the best valve-job?

Thanks for keeping it real
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post #6 of 30 Old 02-06-2018, 07:44 AM Thread Starter
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And for the seat visual ... Intake - exhaust
Attached Images
File Type: jpg Screen Shot 2018-02-06 at 8.43.05 AM.jpg (19.4 KB, 7 views)
File Type: jpg Screen Shot 2018-02-06 at 8.42.28 AM.jpg (22.9 KB, 7 views)
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post #7 of 30 Old 02-06-2018, 08:59 AM Thread Starter
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Just found this video ...
... No active milling or lapping but pretty good overall flow ... Maybe I'll just lapp them a little and go on with the day :-D
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post #8 of 30 Old 02-06-2018, 09:04 AM Thread Starter
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Another thought - are the stock valves SS or titanium? - hard to find and answer. I feel like I am swimming in the deep end of the pool now . HA!
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post #9 of 30 Old 02-06-2018, 11:16 AM
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Stock KLR650 valves are not SS nor titanium. Just good old fashioned Hi-carbon steel.

I dis-agree with the video seat width. But I do understand your lack of proper cutters & their price tag.

pdwestman
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post #10 of 30 Old 02-06-2018, 11:51 AM Thread Starter
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A magnet won't stick to the exhaust valves (does to the intake) and they don't look like stainless ...
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