Jump to content

LZ23 piston valve relief question


budsaipan

Recommended Posts

I have a Z22 block with stock Ka24 pistons on it. Does anyone know if I need to notch the pistons for valve clearance? I've searched and couldn't find any answer to this. I've seen one build thread and didn't seem like that person notched his pistons. http://community.ratsun.net/topic/39329-project-drag-521/page-2 

 

I've also went ahead and put the head on and rotated the cam to check for clearance and it looks like it's hitting the pistons? BTW the valve hasn't been properly adjusted yet. Any info will help. Thanks.

Link to comment
  • Replies 23
  • Created
  • Last Reply

Top Posters In This Topic

Top Posters In This Topic

You have to have the timing chain connected to the cam and crankshaft to do this properly. At TDC of the exhaust stroke is the closest the piston comes to the valves. As the piston rises up, the exhaust valve is closing. At TDC the intake is just barely beginning to open and the exhaust is almost closed. As the engine is turned past TDC the piston drops down well out of the way as the intake valve opens.

 

In addition the KA piston does not even come up to the top of the block. It stops 1.55mm below the deck so you have even more clearance, plus the tiny dish.

  • Like 1
Link to comment

If your just turning the cam over, it will hit. If it's timed, probably not, big camshaft? Put some clay on the piston and turn it over and see what your piston to valve clearance is. If you have big valves or a big cam or both you need to check this.

  • Like 2
Link to comment

Mike and scooter, that makes total sense and your assumption is correct that it's not timed yet. I've just noticed once I mocked the head up, the cam made some scratches from the valve so I got worried. I believe that was the exhaust valve too! 

 

I do however have bigger cams Racerbrown 325r so I'll double check but I think I should be ok since I have stock valves.

 

Thanks guys for the quick response!!!

Link to comment

Sounds like you have some engine math to do.

 

If you want to check the piston to valve clearance, try getting some soft valve springs, or mock up springs and install them on the #4 intake and exhaust valves. Put a dial indicator on the tip of each valve and then run the piston up to and then past TDC while checking the P to V clearance on each valve. The cam has to be properly timed to do this.

 

Custom engine building does require some accountability on the builder, so if you are that guy, then it's ultimately up to you to make sure all the pieces you bought fit together.

  • Like 1
Link to comment

I always try for .100" on 2-valve engines, just to keep safe from an accidental over rev resulting in valve float.

4-valve engines with smaller, lighter valves, and typically much less valve lift, I may venture down to .060" clearance.

 

And yeah, the modeling clay thing works great, and once you turn the engine through the TDC on over lap cycle, I use a razor blade to cut strait down through the clay to get a cross section of the clearance area. 

Link to comment

No, I mean really soft springs. Like springs you would buy at a hardware store for making home craft stuff with. A bobble head doll would use a spring this soft.

Like bic pen spring, but big enough to fit over the valve. You can do it without a spring entirely but its a pain in the ass

  • Like 1
Link to comment

.050" is what I would shoot for on a race motor. Same for the street? Sure, why not.

Thats pretty tight.....

 

What do you run for piston to head clearance in a race motor? Ive run .030 with success, any less its been mixed, some have had pistons kiss the heads, some were ok... Or if you have a reallllllllllllllly loose motor you could kiss a head even at .030...:p

  • Like 1
Link to comment

Set my race engines up with .030" piston to head clearances, without any problems.

 

Had a 125cc flat track bike that I ran at .016", and it would just start to kiss the head at about 16,000 rpm, and make a huge racket through the cooling fins on the head.

It was like an audible rev limit alarm, to tell me when to shift   :)

Never hurt anything, since the bike always had a forged piston.

When the head was pulled, you could always see a light contact mark around the squish area.

Link to comment

Nice, alot of great information.

 

Now, since we are talking about valves. What kind of valve spring compression tool do you guys use? I've used about 4 different style and have yet to find one that really works without the cam towers on the way. Wish there was one that I dont have to fight to get those off and on.

Link to comment

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
×
×
  • Create New...

Important Information

By using this site, you agree to our Terms of Use.