Valve Adjustment

[csmutty]

So I basically have NO experience with 4 strokes besides changing oil and filters. I have come to the conclusion after replacing the carbs and such on my 86 GSXR1100 that the valves were actually the problem, as it wouldn't idle and the power was choppy. So I took off the gas tank, oil radiator, valve cover, etc. Now I have been told by the mechanic at the shop I used to work at that you need to have the piston at TDC on the firing stroke to adjust the valves. My question is how do I know when it is on the firing stroke?

Thanks. And please let me know if there is any way that I can fuck this up lol.

[Fitz]

Suck - Squeeze - Bang - Blow

When you say TDC on the firing stroke, do you mean the compression stroke prior to the plug firing? If so, pull the plug on cylinder #1, block the hole with your finger and feel for compression.

Fitz

[csmutty]

Suck - Squeeze - Bang - Blow

When you say TDC on the firing stroke, do you mean the compression stroke prior to the plug firing? If so, pull the plug on cylinder #1, block the hole with your finger and feel for compression.

Fitz

Ahh ok. So you are saying that when the cylinder comes up the exhaust valve will be closed so the air will only have the spark plug hole to come out....clever. Thanks.

[Fitz]

shrug.. 4 stroke makes sense to me... 2 stroke? The cr125r in my garage? No clue whatsoever....

Fitz

[csmutty]

shrug.. 4 stroke makes sense to me... 2 stroke? The cr125r in my garage? No clue whatsoever....

Fitz

I wish I had your situation. 2 strokes are cake. 4 strokes, I understand the basic principles and parts...but the whole teardown thing just scares me haha. The whole taking off the valve cover and not being able to see a piston...kinda sucks.

[butcher bergs]

Now I have been told by the mechanic at the shop I used to work at that you need to have the piston at TDC on the firing stroke to adjust the valves. My question is how do I know when it is on the firing stroke?

This in not true at all. The only thing you need to do is have the cam lobe facing away from the bucket and take you measurement from there. It's really that simple.

The only place you need to care about timing is when you remove and reinstall the cams.

[FTMS]

Once you have the right spot for one cyclinder it will not be right for all. You will have to rotate the motor for each cylinder depending on firing order. Not a big deal just an extra step.

Is that motor shim under bucket or tappet style adjuster?

[stoinkythepig]

Once you have the right spot for one cyclinder it will not be right for all. You will have to rotate the motor for each cylinder depending on firing order. Not a big deal just an extra step.

Is that motor shim under bucket or tappet style adjuster?

Pretty sure it has screw and locknut adjustment with one cam lobe and a forked rocker for each pair of valves. No tappets and no shims.

Tips:

Inadequate lash usually only causes hard starting when cold, not choppy power or an inability to idle. Excessive lash won't cause any noticieable problems other than noise. I'm thinking vacuum leak and/or clogged pilot jets, but it's a good idea to measure/adjust the lash, regardless.

A key to longevity is adjusting the lash of each valve in each pair exactly the same. Otherwise, there's uneven loads placed on the rocker/cam interface that can cause pitting and fissures on the hardened cam lobe or the rocker.

Adjust the lash to the largest allowed in the measurement range.

[Kurlon]

Plugs out (makes turning the engine over easier)
Rear stand or some other way of getting the rear tire off the ground so you can rotate it
Bike in 6th
Long screwdriver in the plug hole of the cylinder you're going to work on as a feeler for TDC

You can 'bump' the engine by rolling the rear wheel forward, use the screwdriver to watch for TDC. You'll feel it come up, slow slightly and then drop. You need to stop when the screwdriver is pushed out the most. A couple times rolling past you'll get the idea. Now, when it's at TDC look at the valves for the cylinder you're working on, they should be closed on both the intake and exhaust. If it's a shim based system, the lobes will be pointing away from the engine, up at you. If it's a rocker and tappet setup, the lobes will be pointing down and away from you.

While you don't have to be PERFECTLY on TDC, the more duration your cams have the less margin for error in crank position you have. Given that you should be able to land right on it via varying 'bumps' from the rear wheel, I'd shoot for perfection.

Also, the motor must be STONE COLD for this. A 15 min cool down after running is not long enough, let it sit for at least an hour before tackling the valves.

[Cerberus]

Pretty sure it has screw and locknut adjustment with one cam lobe and a forked rocker for each pair of valves. No tappets and no shims.

Tips:

Inadequate lash usually only causes hard starting when cold, not choppy power or an inability to idle. Excessive lash won't cause any noticieable problems other than noise. I'm thinking vacuum leak and/or clogged pilot jets, but it's a good idea to measure/adjust the lash, regardless.

A key to longevity is adjusting the lash of each valve in each pair exactly the same. Otherwise, there's uneven loads placed on the rocker/cam interface that can cause pitting and fissures on the hardened cam lobe or the rocker.

Adjust the lash to the largest allowed in the measurement range.

not true. inadequate lash can cause hot start issues (usually not cold start issues) since the lash (clearance) usually shrinks as the engine warms up. in extreme cases, it can require waiting for the engine to cool in order to restart it, and loss of power while at full temp.

[Cerberus]

Plugs out (makes turning the engine over easier)
Rear stand or some other way of getting the rear tire off the ground so you can rotate it
Bike in 6th
Long screwdriver in the plug hole of the cylinder you're going to work on as a feeler for TDC

You can 'bump' the engine by rolling the rear wheel forward, use the screwdriver to watch for TDC. You'll feel it come up, slow slightly and then drop. You need to stop when the screwdriver is pushed out the most. A couple times rolling past you'll get the idea. Now, when it's at TDC look at the valves for the cylinder you're working on, they should be closed on both the intake and exhaust. If it's a shim based system, the lobes will be pointing away from the engine, up at you. If it's a rocker and tappet setup, the lobes will be pointing down and away from you.

While you don't have to be PERFECTLY on TDC, the more duration your cams have the less margin for error in crank position you have. Given that you should be able to land right on it via varying 'bumps' from the rear wheel, I'd shoot for perfection.

Also, the motor must be STONE COLD for this. A 15 min cool down after running is not long enough, let it sit for at least an hour before tackling the valves.

semi-agreed
i usually would set the lobes so they are pointing straight up, which is to say straight away from the tappet to minimize the chance of being on an opening or closing ramp of the lobe.

[csmutty]

Wow. Thanks for all the info guys. I'm going to try and tackle this now. This is much more info that I had expected. Way to be
And this bike hasn't run for 6 months or so, so I think it's cold enough. I am just hoping this solves my problems haha.

[Kurlon]

Oh, one more thing, have you check the brakes?

[csmutty]

Oh, one more thing, have you check the brakes?

Have I checked the brakes? There are new pads on front and rear...if thats what you mean.

[Cerberus]

oh yeah, one more potential problem caused by zero lash or even negative lash is a burned exhaust valve, because the exhaust valve dumps a lot of its heat to the seat, and if the negative lash means it never gets to the seat, it can't dump its heat..

[Rambunctous]

shrug.. 4 stroke makes sense to me... 2 stroke? The cr125r in my garage? No clue whatsoever....

Fitz

Just one big pump.

[Rambunctous]

shrug.. 4 stroke makes sense to me... 2 stroke? The cr125r in my garage? No clue whatsoever....

Fitz

Just one big pump.