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Valve Replacement Questions....

  • Thread starter Thread starter Dave_A
  • Start date Start date
D

Dave_A

Guest
Ok, I'm replacing the valves on my 450 (2-valve per cyl, 2cyl motor), and I have questions...

I have the clymer manual that describes valve installation, but it mentions nothing of shims, or other things I've heard I need to do.

I'm looking for an in-detail description of everything I need to do/measure in order to install valves (i.e. starting after 'unwrap valves and sort valve pieces')...

How do I measure shim size? Is there anything else I should check (the guides seem fine: the valves don't wiggle around (they're loose enough to move up and down freely, but that's it) when they're just slipped in place, so I assume this means my guide is fine)...
 
The clymer manual will have valve shimming in the general maintenance section near the beginning.

You can check the valve stems by putting a bit of oil on the stems. After you put them in put your finger over the stem hole and pull out the valve. If you hear a "pop" your stems should be fine. Note that this is the cheap and dirty method...you need a dial guage to do it as per the book (50$CDN or so for the guage).

Steve
 
Ok...

Let me see if I get this right (from the manual)...

To measure shim clearance, turn the camshaft so the pointed lobe-tip that operates the valve being measured is pointing UP, away from the valve...

Then measure the space between the non-pointed end of the lobe and the tappet. If it's between 0.3 and 0.8, you're fine, otherwise change the shim...

Is that about right???
 
Why are you replacing the valves? I can only think of 4 reasons - stems are worn or they are bent, burnt, or cracked. In any case, this is a job for a machine shop.

Do you mean you are adjusting the valves?
 
Swanny said:
Why are you replacing the valves? I can only think of 4 reasons - stems are worn or they are bent, burnt, or cracked. In any case, this is a job for a machine shop.

Do you mean you are adjusting the valves?
Click to expand...

Timing chain skipped, valves hit pistons & bent, time for new valves...

I had the guides checked, the shop said they are OK, so I just ordered new valves... I am NOT replacing the guides (I know this is a 'shop-required' job, as the guides must be pressed in)...

What exactly would I need a machine shop for? I mean, it's just a matter of re-assembling the valve parts, compressing the springs (the tool to use looks like a big C-clamp, I can rent one from my local auto parts store), and then adjusting the tappet shims for proper clearance... It's the last part I'm not quite clear on...
 
if you fit new valves you lap them in use valve grinding paste there is a tool with rubber sucker on end these are cheap if you lap the valves there is a risk of them not seating and you could burn a valve
ozman just a thought
 
I have never lapped my valves - auto or motorcycle. I have heard of people doing it, but when they lap the valves it was my understanding that it was after a valve job in order to get a better seal.

One thing to keep in mind is that while the valves are new and have a nice new seat, the valve seats have been abused by both time and the bent valves. They need to be at the proper angle and width to function properly. Lapping was not intended to replace this machine work.

If it was my motor I would send the head to a machine shop for a proper valve job, but it is your call.
 
if you are putting new valves in new head lapping not required new valves into a valve seat that has wear you should lap obviously you are right to say best left to expert but some people like to d.i.y
ozman
 
after reading your other topic i think you should go to a mechanic
ozman
 
You need to lap the valves in order to see where they face of the valve contacts the seats. This also tells you whether or not your seats are damaged as they will not have gotten scuffed by the compound anywhere there is a low spot.

Steve
 
srivett said:
You need to lap the valves in order to see where they face of the valve contacts the seats. This also tells you whether or not your seats are damaged as they will not have gotten scuffed by the compound anywhere there is a low spot.

Steve
Click to expand...
Once you've done that, make sure the head and valves are hospital like clean. You don't want any of that lapping compound running around in your motor! Assemble the head with the springs and keepers etc, and then turn the head upside down and fill the combustion chambers with solvent. If you see anything leak into the intake or exhaust ports, you know you have a valve that is not seated. 8)
 
The head was taken to my local shop to have some stuck bolts extracted...

They said the seats/guides checked out...

I was thinking about having a valve job done, but that's still up in the air...
 
Ok...

I went to my local auto-parts store and bought a valve-lapping kit...

Did that, ground nice even rings into the valve seats, and I'm ready to re-assemble...

Problem is, the only valve spring compressor I can get is designed for Chevy V8 valves (where the spring, retainer, and keeper all stick out of the head about 2 inches). Since the GS valves are down in the head, the automotive compressor won't compress them...

So I'm gonna take it back to the shop that pulled the stuck bolts out, honed my cylinders, and removed the valves, and ask them how much to put the valves back in...
 
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