Recommendations, boring, ballancing

[Mekanix]

I agree mawg, If I could get the volume needed I would go that way.

The original design had no side quench areas, Only front and back.

I'm trying to keep it the same by blending the sides into the bore diameter.

I gained 4.5cc's from that alone.

The next thing I'm going to do is unshroud the valves.


The middle is a little harder to work with but I will try.

I'd like to avoid the areas between the valves and spark plug. They do crack there, so the more material there is, the better.

[mawg]

Oop's my mistake. Looked back at your post147 and I see what you mean.Looks good so far, and I think I see where on the intakes at least your can go a bit more, at about 1:00 on the top intake valve and 5:00 on the bottom in your last pic?Maybe 1-2cc's more in the chamber leaving 4 or 5cc's in the piston at eleven to one.Yahoo- getting there.If you can mill the piston 1.7 mm that is.But what other pistons could you use if you can't safely mill that much?I'm just wondering if turbo pistons can be gotten in your bore and pin size and hight. Then couldn't you mill the tops of the turbo pistons to get your desired dish volume?What if you could get 6 or 8cc's that way and could then begin another round of base and cylinder head gasket juggling to get the best deck hight and quench?Would you do it?Or am I delusional?

[Mekanix]

I'm not sure what else has this type of piston but I would try anything if I could find it.

Maybe a Honda civic piston ? looks close by eye but I haven't measured anything yet.


I managed to get a little more of a blend around the valves going outward to the sides. I'm at 5cc's now. I only need 3 in the piston and there is already 2 in the valve reliefs.

The next thing to do is cut valve reliefs in the piston or drag the existing ones in.

I've thought about using my spare head and a modified valve to cut the reliefs into the piston by notching one corner of the valve and spinning it by drill down to a set point.


How would I know how deep to go ?

I know there isn't a point where the valve is fully extended with the piston all the way up but when are they the closest?


I suppose I have to mock it up to find out. Its just hard without knowing the overlap. Also with the stock piston it only took 1 tooth off to cause contact so the valves definitely come close.

how much space should I have between the valve and piston ?

1mm?





Progress since last update: got 124 link timing chain installed. Might have to remove 2 links.

Cleaned up and matched combustion chambers. Thinking of polishing exhaust ports. lots of carbon buildup.

[Mekanix]

At what Point will the valve's be closest to the piston ?


I know the exhaust valve is moving out of the way as the piston rises on an exhaust stroke and the intake is opening, not fully open before the piston passes through TDC but continues to open as the piston moves away.

At what crank degree/ piston position does the intake valve come closest to the piston?

[7981GS]

Bolt it all up with modeling clay in the valve reliefs.
Turn the engine a few revolutions and measure the distance that the clay has squished to.
You can assemble with old head gasket to test.

Eric

[Mekanix]

I don't have the valve reliefs cut in the pistons yet. The existing ones are 4mm too far out to be useful. I could get maybe 1/2 revolution before the valves would definitely hit.

I'm just trying to wrap my head around when everything happens so I can plan how deep I should go with the valve reliefs. Or if I just dragging the existing valve reliefs the 4mm towards the center would be the best thing to do.

Either way I'd like to have the reliefs done in a mill instead of the way I was originally going to do it.


(that was by using a spare head and valve modified with a cutting tip as a makeshift mill)

[7981GS]

Add spacer washers between the head and cylinder until they don't hit.
Measure your spacers and add the recommended .030 to that figure. I go to .040 to be a smidge safer.

Eric

[GregT]

Exhaust valves will be at their closest point to the piston between 15 and 10 degrees BEFORE overlap TDC. Exhaust valve closing and the piston chasing it...
Inlets closest betwen 15 and 10 degrees AFTER overlap TDC. Piston dropping and the valve chasing it...

Actual degree figure depends on how agressive the cams are and the lobe center figures but this range pretty much covers it.

[rapidray]

Add spacer washers between the head and cylinder until they don't hit.

Eric

Are you NUTS or just never had experience in building an engine & doing the MATH required to do one?!!! Look Mekanix, feel free to call me at 714--356-7845 if you want some help with this build & I will share some info that will help you. Eric, you need to stop posting about stuff that you OBVIOUSLY have NO experience with before you cause someone to damage their stuff!! Ray.

[rapidray]

Exhaust valves will be at their closest point to the piston between 15 and 10 degrees BEFORE overlap TDC. Exhaust valve closing and the piston chasing it...
Inlets closest betwen 15 and 10 degrees AFTER overlap TDC. Piston dropping and the valve chasing it...

Actual degree figure depends on how agressive the cams are and the lobe center figures but this range pretty much covers it.

Good post Greg & let me add the following: For each degree you move the cam timing, you will add or lose .016 in piston to valve clearance, depending on which way you go. Let me know if I can help, Ray.

[7981GS]

Never had a valve hit a piston, thanks for your concern.

Eric

[Mekanix]

Exhaust valves will be at their closest point to the piston between 15 and 10 degrees BEFORE overlap TDC. Exhaust valve closing and the piston chasing it...
Inlets closest between 15 and 10 degrees AFTER overlap TDC. Piston dropping and the valve chasing it...

Actual degree figure depends on how aggressive the cams are and the lobe center figures but this range pretty much covers it.

That's what I was looking for.

Good post Greg & let me add the following: For each degree you move the cam timing, you will add or lose .016 in piston to valve clearance, depending on which way you go. Let me know if I can help, Ray.

Thanks Ray, Thanks Greg.

That's the information I needed to know.

When I'm finished, hopefully the top end will be as close to the stock valve reliefs for depth as I can make it.

All I'm really asking for is: If I needed more valve relief by moving the cam a few degrees, how much extra clearance should I ask for when I have the reliefs cut.

[mawg]

Well you could use Eric's washers and modeling clay to determine where the new valve reliefs need to be,and .040 or 1.2mm does ring a bell for piston to valve clearence (at least on auto pistons).Rapid Ray, whos built a ton of engines is willing to share his knowledge with you.I hope you'll consider calling him and posting any results.Knowledge is power,after all.

[Mekanix]

I called Ray. He's interested in helping me out.

I know how much i should take out to make the new pistons the same as the stock ones. I just needed to know how much extra to take out in order to play with the cam timing.

.

[Mekanix]

Got a base gasket for a gs500 today. Its metal and .25mm (0.010") thick with a bore of 82mm.

Looks like this.


I got it just to see if it would be useful but I don't think I'll use it unless I need a small change in height.

It was only $7 after all.