Valves, re-use or replace?

[yaddy]

Moved this part of my build post to the technical section, just stripped the top half of my engine, any advice on the valves please?

Quote:

Here's what 30,000 miles looks like:

Pulled the head off and saw these pistons, i have to say at this point i was pleasantly surprised at how clean everything looked, i know it has a decent carbon build up but i expected a lot more.

Then i flipped the head over and realised it was as bad as i expected, haha. Check out the white-hot exhaust valve on no2 cylinder.

Closer inspection here reveals a crack in the exhaust valve, 1 of the studs has been snapped off from the head that secures the exhaust clamp, obv this is why the valve has run hot and cracked. Best add new valve/s to the list of parts then.

Any advice here? I've already ordered new rings, circlips and gudgeon pins, got new stem seals too. when i remove these valves and mic them up, if they are within Suzuki tolerances, would it be ok to use the existing valves and just replace the one damaged exhaust valve, or is it best to play safe and replace the lot? A friend says if the old valves measure ok and are lapped in sufficiently, there's no real benefit to replacing them, does anyone agree with this?

 

[Nessism]

I agree with your friends recommendation with one note of caution: the factory spec and service limit can be a little misleading. Suzuki lists both a specification range for the stem diameter and a service limit. If the valves measure outside the normal specification range, you can be sure that the valve to guide clearance will be out of spec (this is the critical thing, not the stem diameter per say).

For example: in rebuilding a GS1000 head I have valves that all measure within the factory specification range, yet several of the valves (exhaust side mostly) have excessive clearance to the guide - guides need to be changed.

Hope this helps and good luck.

 

[rustybronco]

Then i flipped the head over and realised it was as bad as i expected, haha. Check out the white-hot exhaust valve on no2 cylinder.

Closer inspection here reveals a crack in the exhaust valve, 1 of the studs has been snapped off from the head that secures the exhaust clamp, obv this is why the valve has run hot and cracked...

Not so obvious. a vacuum leak on the intake side will make it run lean.
The intake valve will be on its seat, conducting heat away from it. while the exhaust valve being open, will be taking the brunt of the higher exhaust temps.

 

[trippivot]

the carbon build up is what was controlling your timed ignition -- not the spark plug-hence the valve damage. combination of both pre-ignition and detonation.

de-carbon everything and get 1 ex valve. $25.00 NEW here in USA

grind seats re face valves set installed heights and set valve spring seat pressures -call it good.

 

[82Shafty]

I'm with Ness on this on:

1) Ensure your guides are in good shape

2) After you clean the combustion chamber ensure that there aren't any cracks between the valve seats... use a dye penetrant

3) Also remember that the valvetrain is going on 30 years old, springs should be replaced and while you certainly can reuse the remaining valves if the others spec out, I'd be a little leary of it. On top of the age, you have countless heating and cooling cycles that you maybe looking to slam the valves open and closed up to 9500 on this thing, I'd hate to see you drop a valve for trying to save a few bucks. You know your riding style, if you're the type who might see redline once a riding season then I wouldn't worry about doing all of the valves.

4) Any normal carbon build up is usually pretty flakey, from what the pictures are showing, it kind of shows "some" oil consumption as well.

 

[yaddy]

cheers for the info guys, checked the old MOT's and clocks today, it's actually covered 47,000 miles! Dunno where i got 30k from (wishfull thinking probably).

Took the references from the Suzuki manual for service limits and here's where i am now:

pistons = ok
cylinders = ok
rings = shot (nearly 2mm gap in top rings when inside bore)
cam chain = bang on the service limit
valves = all the stems are within limits
guides = not sure how to measure the stem to guide play. Got a dial gauge from the engineering shop up the road (paid a few quid to borrow it for the day, have to return it tomorrow afternoon). In the manual, it shows measuring the play on both axis (north to south, east to west so to speak), my question is, "how far out of the guide should the valve be to measure with the dial gauge?" Can't quite make out from the picture as to whether the valve should be sat flush with the head or level with the top of the dome etc. Anyone have any ideas on this?

Quote:
"You know your riding style, if you're the type who might see redline once a riding season then I wouldn't worry about doing all of the valves."

I do tend to give a bit if i'm honest but that's what my R1 is for. This is supposed to be something to go pottering about with my Dad on, just got him into jap stuff and away from the british gear (nice to look at but not much fun to ride!), my opinion only...........