mark kibort

i know you are, but what am I??

Hey, I didnt mean to come accross condescending, but i really wanted to know why you are claying it up. Do all the strokers that get built having the engine clay'ed up?

second, when you gave the situation of you claying things up, and the clay was not touched, yet it still bent valves, basically it seemed to me like that was a qualifying test.

so, i get it that we all know our engines are interference. No, scots, even with the valve cuts, is certainly not non-interference. Im not sure about euro 82's though. However, my point was the fact that the 4 valve pistons have very shallow valve cuts. If the heads are such that the valves dont travel down as far as they do with the 2 valvers, maybe a deeper cut could be benificial. measuring valve depresssion to contact can tell a lot about this possibilty.

I think with some race engines, as you seem to agree, those cams might be so radical that they need to clay timed out, due to that accelerated valve distance

with our cars, and the stock GT or S4 cams, the spec is only 2mm valve travel for 20degrees of crank rotation. and we all know that the valves willl be open at full max at somewhere near 90 degrees. and the valve chases the piston at an angle. so, im sure you can roughly calculate it out to see if the max lift of a cam and valve will ever get to hit the face of a piston when timed out.

so, i ask, is it really needed to check the stroker engine build up, even with a cam like anderson has which is only 1mm more lift than a GT cam?


mk

mark kibort

i just measured the euro piston valve cuts (82). they are near .3" to .35"(intake) Now, since my valve reliefs on my 5 liter euro were .175". and nothing touched until the valve was depressed .3", it might be safe to say, that if the max lift is under .5", there is no way that a euro 82 can be an interference engine

Mk

John Veninger

I can't answer for others. This was my first stroker build and I was making sure I checked everything I could. As you know, a Stroker motor consumes a large bunch of cash. I wanted to make sure it ran when I turned the key (well actually pushed the button!).
My cams have more than an additional 1mm lift over the GT cams.

Here is a picture of the valve cuts during the first build:

mark kibort

wow, those are some deep cuts.

I know you were trying to physically check all factors that could lead to a problem.

With those cuts, im amazed how the valves hit. maybe they just barely hit

Those look like the cuts we made with the 2 valve 5 liter. I guess you might have been in the same situation, where the valves still hit at about .3 to .4". if you have more than the GT lift, or somewhere near .5mm lift, that is the reason. It would be interesting to know the distance between the piston and valve as it travels down. If it is anywhere near the 2valve design, it is near .175"

When is the next track event?

mk

John Veninger

Nope, they hit HARD!. I'm having problems getting a few out since the springs are so compressed that I can't compress more to get the keepers off!
I'll take some pictures soon

Well us winter folk have to wait until spring. Motor is on the stand right now.

mark kibort

ouch! well, those cuts look like .175" at least, so what is the cam lift you are using ?(or is that top secret?)

put that motor at TDC and lever down a valve until it hits (touches) I bet its got to be close to the .45" range. but i guess when the valve comes down and there is even 1mm of a problem its going to hit "hard"

mk

928SS

IIRC, there is a guy in CA that's having tim build a NON-Interference 7L motor. the pistons are custom jobs w/pretty big valve reliefs... seemed like a cool idea.. he was at sharktoberfest this year... maybe someone knows his name and he or tim m. might have a clue on how to do that... could be a real cheap mod that could save us a lot of pain...

mark kibort

So, i just was thinking more about this. You said you clay'ed it up , timed it and then turned it over. as we know, there is a pretty good chance that the pistons would never touch the valve pockets and thats what you found. Now, what did that proove? well, you have valves that dont touch the pistons while it is timed correctly. but what about checking the valve pockets? you will never know if those are correct, unless you push down a valve and hit the clay and pocket area? right? what if, for example, they were not done correctly, or were off like Scot's were? well, that would or could be an impact zone where if they were correct, you could have a non interference engine.

did you see any marks on the pistons resulting from the impact?

The entire point of what I have been talking about is seeing how much room the valve pockets buy you, and if they are done correctly. (meaning when the valves come down, they dont hit the edge of the valve reliefs and then bend valves if a belt were to slip or break)

so, excuse my ignornace if im off base here, but with all the checks of non stock parts, how is this critical factor checked?? claying and timing the pistons doesnt seem to address it at all. It seems obvious now that ive done a few of these, that checking the valve pocket clearance valves and alignment is a critical factor.

mk

mark kibort

Also, from the look of the pistons, it looks like the valve pockets are still not as shallow as the "valley" of the pistons. does there look like there is more room to take out a little more pocket area? does anyone know the depth of the "valley" or "dished" area? more than .2"?

again, what were your lift values on the cams?

and, by the way, did you loose only intake valves or exhaust valves in the failure? we all know that the lifts are usually differnt from exhaust to intake, and the stock 85 4 valve piston has differnt valve relief depths for intake vs exhaust.
mk

mark kibort

John, You got me thinking about the failure. Did you do any of these checks that i mention below?

Mk

John Veninger

No, I did not. Wasn't making a non-interference engine and claying the motor told me everything had enough clearance.

Yes, you can see the hits on the pistons in many places. Yes the exhaust hit, but not as bad.

mark kibort

But, the reason for the valve pockets is really for moving the cams when the belt is not on, and when a piston might be near TDC, or for a safety margin when a belt slips a few teeth like it did for me. Is there any marks on the edge of the valve reliefs? showing that they were not cut perfectly for the valve position?
again, if i had assembled scots engine without checking that, the engine would have been fine, until a belt or even during assembly process, when the valves could hit the side of the valve pockets for not being cut perfectly. Close, and exact replica of the cuts on the smaller pistons, but for some reason, just about .25mm off. thats all it takes to cause a problem, so i ground them down 1-2mm to make sure the valves wouldnt hit the sides of the pockets.

when i build up the stroker, im going to get that value of the distance of piston at TDC to valve touching the piston. I suspect its near .3" as well. Meaning, that with a stock GT cam lift of near .45 (i think) a deeper cut on the valve reliefs by .2, might make S4s non interference.

Am i way off base here being a shade tree mechanic/engine builder, or why wouldnt have the pro builders evaluated this before?

mk

kjurkic

What about piston & con-rod "stretch"? The length of these is dynamic through rpm & temp, but is it enough to cause impact?

Perspiring minds want to know!

K

Jim bailey - 928 International

Care to cite a source for this..."But, the reason for the valve pockets is really for moving the cams when the belt is not on, and when a piston might be near TDC, or for a safety margin when a belt slips a few teeth like it did for me."..... ???? Porsche instructs you to lock the 32 valve engine at 45 degrees off TDC BEFORE removing the belt , pistons halfway up or down and not move it until the cam timing is correct.

adrian928se

John V, when you checked the clearances, did you replace the hydraulic tappets with a solid/modified lifter set?

Adrian