Author Topic: Changing a exhaust valve, easy to do??  (Read 68 times)

Offline Numewsm

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Changing a exhaust valve, easy to do??
« on: March 15, 2019, 10:01:52 PM »
Going on from my previous threads about changing tight shim buckets, my 500F is still popping and burberling with no choke effect.  MPG is poor, but it still starts and runs.  Can rev out in 1st to 3rd gear but not as fast as it was, then struggles in 4th and 5th. no acceleration power unless in high revs.  Checked the plugs and the right is ok in colour but left is black.
So suspect the left exhaust valve is coked up or burnt, as this shim bucket was tight and not always fully returning to its full height with no cam pressure.
Question is, is the replacement of this valve easy to do at home? as in lapping the valve and valve seat? Obviously I would check all the valves and their seating whilst its apart.
Or remove the head and pass to a bike workshop to do?
Any idea what the approx cost (£sterling) would be for a workshop to complete.
I would guess that i would have to replace both head gaskets top and bottom to prevent any oil leaks?
I have no problems doing it myself, once i get the exhaust bolts off which look like they've never been removed!!!!  :o :o :cry: so i'll replace them anyway
I ride because it gives me the space to empty my mind off all that is bad and refill it with good.

Offline Falken Hawke

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Re: Changing a exhaust valve, easy to do??
« Reply #1 on: March 16, 2019, 04:00:41 AM »
It's not difficult but some precision is required.

Things to be careful with:

Don't go overboard seating the valve(s).  Using markup dye (prussian blue, seating compound) check the valve, lightly grind, check the valve, repeat until the valve is seated.

Ensure the head is flat.  Check with a straight edge across three sections (front, center, rear) longwise and diagonally.  If it's not flat, a trip to the machine shop is in order.  There is an allowable deviation but I don't have the numbers readily available.  Typical is some x/1000th of an inch checked with a feeler gauge.

Don't lose the cam timing.  The shop manual will have a procedure as well if the timing is lost.

Don't gouge mating surfaces when cleaning them.  Head gaskets like to stay put so getting them off involves using a scraper.  Even a plastic one can gouge aluminum if one is aggressive so be careful.

Ensure there is no oil or other liquid in the headbolt holes.  Liquid does not compress so any in those holes will not allow the bolts to clamp the head completely.

The headbolts must be installed progressively with a torque wrench.  The shop manual will have the procedure.

Eye protection.  High tension springs and small parts.

Take pictures before removing anything.  Take pictures of what gets removed.  Continue as things are removed.  Post photo blog when done reversing procedure :)

Replace all the gaskets involved.  Also note that a small amount of sealant is required for the camshaft cover gasket.
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Offline Numewsm

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Re: Changing a exhaust valve, easy to do??
« Reply #2 on: March 16, 2019, 01:02:42 PM »
Many thanks for your advice, much appreciated.
 :bowdown: :bowdown:
Think I will do it myself, save a few pennies. But if I look at it and think no. I'll take the head to the local bike shop and get them to do it. The strip down will be most of the garage cost which I can do with no issue.
I ride because it gives me the space to empty my mind off all that is bad and refill it with good.

Offline Bluesmudge

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Re: Changing a exhaust valve, easy to do??
« Reply #3 on: March 16, 2019, 09:46:35 PM »
Another option is to source a used head that is in good shape to swap over. They often show up for $100 - $300. That is what I did when I bent a valve after incorrectly setting my timing. As a novice mechanic this was much easier than changing the actual valves.
Then all you need is a full set of top and bottom head gaskets, copper washers for the head studs, and maybe a cylinder hone drill attachment to knock the glaze off the cylinders.

Same advice applies for making sure the timing gets re-set properly once you put it back together. Make sure you know how the cam chain tensioner works.
« Last Edit: March 16, 2019, 09:48:08 PM by Bluesmudge »

Offline Numewsm

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Re: Changing a exhaust valve, easy to do??
« Reply #4 on: March 16, 2019, 11:45:29 PM »
Thanks Bluesmudge. no probs with the timing, done it a few times now. i put a youtube video up about it as there isn't much on the internet about how to do the timing on 2004 and up GS's,
I ride because it gives me the space to empty my mind off all that is bad and refill it with good.