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Mechanics 101 Can't get it to run right? Find a trick to add HP?
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Old 04-01-2010, 01:25 AM   #1
dagda
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Default What's the purpose of a valve clearance adjustment?

Hello,

I just got my first Katana ('02 750). I've had other bikes, but haven't had to do much besides carb work. It has a little over 8,000 miles on it. It looks like it wasn't taken care of very well. I've been going over it and have noticed multiple problems like loose centerstand bolts, rusty & loose chain, etc. I am fixing everything I can now before I start riding it, so I know what I'm working with. I've been reading my service manual, and I believe it is time for a valve clearance check/adjustment. My question is how important is this, and is this a good time for that?

Thanks
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Old 04-01-2010, 01:33 AM   #2
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A valve adjustment is very important to the proper running of the bike.

What your doing is adjusting the timing of when the intake and exhaust valves open during the operation of the engine. If the timing is off a little, you end up loosing out on engine performance by not allowing the proper amounts of fuel mixture into the chamber for combustion and or not allowing the burnt exhaust fully out. The more optimal this is, the better the motor runs.

When it gets way out of wack, you end up with broken parts/engine that stops running eventually because the valves/pistons get dmged.

Now is a very good time to do it. Be sure once you do, to follow that with a carb sync as a valve adjustment will change the vacuum of the different cylinders. Syncing the carbs helps to bring the fuel delivery back into an optimal delivery.

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Old 04-01-2010, 04:31 AM   #3
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+100 to Krey's advice. Tight valves burn and break.
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Old 04-01-2010, 08:57 AM   #4
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Valve clearance adjustment has nothing to do with timing.
It is however critical to the engines life. Maladjusted valves could effect the flow in and out of the head but there are much more important concerns.

At idle your valves are getting opened by the cams 16 time a second. What you want to happen is for the cam to push open the valve and then ease the valve closed again. At 16 time a second this can only happen if the cam is in correct contact with the shim or the valve and tappet. When the engine is cold there is actually a gap between the tappet and the valve, as the engine warms up all the parts expand. So this gap gets eliminated. This "cold gap" is calculated by the Suzuki engineers. If the gap is too large when the engine is hot there is still a gap and the tappets are basically slamming into the valves 16 time a second. Wind the engine up and while you're "cruising" at 55 MPH in 6th gear those parts are getting slammed 65 times a second. You might as well be in there with a hammer. Now if the gap is too tight the valves never seat. This is a concern for performance because if the valves leak by you're not getting good compression. Add to that the increased exposure of the exhaust valve's edges to the combustion and burned valves and seats can result. This can lead to a vicious circle where the more the valve burns the worse it seats and the more it burns.

IMO you should adjust both sets at the middle of the range. Intake valves are set tighter than exhaust anyway because the exhaust heat more and thus expand more.
If you are new to using feeler gauges you run less risk or going too tight or too loose this way.
The best time to adjust the valves is when you have the bike apart. This make getting at the valves easier. If you have a new-to-you-bike assume the valve haven't been done and do them. Make a note of the mileage. Only do a carb synch after adjusting the valves.

Last edited by Black_peter; 04-01-2010 at 09:01 AM..
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Old 04-01-2010, 09:36 AM   #5
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I broke a valve a few years back while on the hwy
The intake valve snapped off and was trying to exit through the exoust valve. I had to drop the engine, get a new valve, get the exoust valve seat drilled out so the valve would seat properaly. I was out $600 because I was too cheap to get the dealership to do a valve adjustment. I was lucky that I didn't hurt the engine anymore than I did or I would have had to buy another engine. It would have been more than $600 if I had of left the bike at the dealershipand had them dismantle the Kat but since I brought in just the engine I saved $200 according to the owner of the dealership.
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Old 04-01-2010, 11:51 AM   #6
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Quote:
Originally Posted by Black_peter View Post
Valve clearance adjustment has nothing to do with timing.
It is however critical to the engines life. Maladjusted valves could effect the flow in and out of the head but there are much more important concerns.

At idle your valves are getting opened by the cams 16 time a second. What you want to happen is for the cam to push open the valve and then ease the valve closed again. At 16 time a second this can only happen if the cam is in correct contact with the shim or the valve and tappet. When the engine is cold there is actually a gap between the tappet and the valve, as the engine warms up all the parts expand. So this gap gets eliminated. This "cold gap" is calculated by the Suzuki engineers. If the gap is too large when the engine is hot there is still a gap and the tappets are basically slamming into the valves 16 time a second. Wind the engine up and while you're "cruising" at 55 MPH in 6th gear those parts are getting slammed 65 times a second. You might as well be in there with a hammer. Now if the gap is too tight the valves never seat. This is a concern for performance because if the valves leak by you're not getting good compression. Add to that the increased exposure of the exhaust valve's edges to the combustion and burned valves and seats can result. This can lead to a vicious circle where the more the valve burns the worse it seats and the more it burns.

IMO you should adjust both sets at the middle of the range. Intake valves are set tighter than exhaust anyway because the exhaust heat more and thus expand more.
If you are new to using feeler gauges you run less risk or going too tight or too loose this way.
The best time to adjust the valves is when you have the bike apart. This make getting at the valves easier. If you have a new-to-you-bike assume the valve haven't been done and do them. Make a note of the mileage. Only do a carb synch after adjusting the valves.
Hey look, we said the same thing... :

Krey
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Old 04-01-2010, 12:20 PM   #7
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Thanks for the info. I understand the purpose now. Are there any details the Haynes manual leaves out? That is what I plan to use as instruction for the procedure. It seems like a pretty straight forward task.
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Old 04-01-2010, 12:22 PM   #8
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Slappy valves=Happy valves
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Old 04-01-2010, 12:43 PM   #9
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Quote:
Originally Posted by Kreylyn View Post
Hey look, we said the same thing... :

Krey

I thought that the shape of the cam lobe adjusted the overall timing... and that the purpose of the adjustment was to keep the "correct" amount of slop between a hot and cold engine
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Old 04-01-2010, 01:36 PM   #10
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Quote:
Originally Posted by steves View Post

I thought that the shape of the cam lobe adjusted the overall timing... and that the purpose of the adjustment was to keep the "correct" amount of slop between a hot and cold engine
Yes Steve, You're right.. The lobe and of course the cam chain business..
But I guess that is saying the same thing too.. ??
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