largecar379

why did it let go?

tension wrong?

Please tell.......

--Russ

largecar379

Sorry, didn't look at the breakage thread--that sucks.

--
Russ

mark kibort

you put the heads on the engine, mount the cams and rotate the cams while a piston was at TDC, or did you time it out and rotate the crank and pistons?
I think the easy way would to just clay the piston and push down a valve .5", right? if you timed it out and clayed it, then of course it wouldnt hit, as we all know from timing the engine, 20degrees and the valve only depresses 2mm, and the valves chase the pistons from there, and this is why they might never touch the pistons. So, i wonder, how deep did you made the 968 valve cuts?
Its funny, after all the engine losses, you would think we would all know what clearance we would need to have a non interference engine.

im wondering why with the strokers, that with the custom pistons that are sometimes used, why cant the valve pockets be carved out a little deeper.

mk

daveo90s4

Mark, you said "Its funny, after all the engine losses, you would think we would all know what clearance we would need to have a non interference engine"

I agree, so I've developed the methodolgy for doing this. All I now need to do is 'calibrate' the computer model, and to do that just about all I need now is some end-on digital photos of the inlet and exhaust cam lobes. The model will cover all 928 model cam lobes, and will include the ability to mix and match.

So if anyone can send me some hi-resolution photos of cams (with proper labelling, e.g "1989 GT inlet cam") then I can complete the model.

My email address is
david.overington@rta.ae

Cheers

Vilhuer

Bulgaria starts to sould better and better. Dropped GTS heads to local shop. They said valve seats need to be changed and they would really prefer to use all new valves too. Estimate for intake seat change etc is $1200 plus possibly 16 exhaust and 7 intake valves more, $20 each. Too late to turn back now.

http://www.hicar.fi/cms/FC?link=hicar-frontpage-en

928SS

I wonder if the chicks are cheap too...

John Veninger

I clayed it timed.
Now why would I noe have bent valves if I did it not timed and didn't touch the clay


Have you really thought about what it would REALLY take for a non-interference 32Vengine??

I'll bet the piston is paper thin or holed to cut enough due to the valve angle. The 32V valve angle is much different than a standard 16V valve angle.

marton

About
&

look at the link; the Bulgarian girl who won the competition for looking good in "Sloggi" panties
http://tinyurl.com/yvbjz9

Marton

928SS

does she own a machine shop? could be a winner!

gotta admit, motor work on the 928 is a whole nuther game compared to 2 stroke stuff... kinda makes go cart racing or flying gyrocopters seem pretty attractive again after 2 OH's in 24 months for me. course, hitting something at 120mph w/a bumper seems pretty tame compared to hitting something w/my head. (I know, I know, my head is thicker)

mark kibort

Well, did you think about what you would really be doing by timing it out? what would that tell you anyway. the valves shouldnt touch the piston if it is in time.
if you use stock lifters, and not solid, you might also get some extra clearance if you were to rotate the cam with the engine at TDC.

Yes, ive thought about what it would take for a non interference engine on a 32valve. depending on the lift of the cam, you need what ever depth added to the piston pocket, above and beyond what it takes for piston to valve contact. I would guess it would be near .3" depth. (like a euro 2 valve piston)

the piston is not paper thin, as we could safely machine euro 86 valve reliefs, .175" deep in the 4 valve piston.

did you depress the valve and see how far it needs to be compressed to contact the piston? the valve reliefs on a stock S4 piston is near 2mm. they are almost non exsistant on the exhuast side for the 85 pistons.

from looking at the S4 heads, it looks like the valves travel toward the pistons a little less of an angle vs the 2valve set up.

mk

to answer you question. (i think), you would not have bent valves, if you didnt time it, and it didnt touch the valves because that would mean even at full lift, with the piston at TDC, the valves are not touching the piston.

John Veninger

Mark,
That statement would be from someone who really doesn't understand some principles of custom engine building.
Putting together factory parts lets you get away with not checking some clearances of your assembly. A stroker is not all factory parts.

Mike Simard

What does "timing it out" mean?

mark kibort

John, I understand that the stroker and alll clearnaces cant be checked, but valve clearances can be. You mentioned that you clayed the pistons, timed it up, yet it still it still bent valves. that is spoken by someone that doesnt understand what the valve clearances are actually used for, or how much clearnance you need to keep the valves from hitting the pistons upon a timing belt break. I asked some simple measurements. You didnt take them, so that shows me you were not really concerned with the pistons hitting the valves after a timing belt break. (or should i say, you were accepting of the interference qualities of our engine design)
again, with the 5 liter build ups, you can take quite a bit of material from the piston valve cut areas for 2 valve cust, and certainly you can do this with the 4 valve set ups. Now, areas that im not familar with, is that some of those valve pockets might effect combustion flows, or create hot spots. However, i do hear of engines that dont grenade upon a cam chain or belt breaking. I think we need this with out cars!

There are a few things i found on the engines i built, that were difficult to check for spec, so we rotated and checked for things that rubbed. found a few things! i depressed vavles, and found that even though the pistons had the identical to spec (or to the master template) cuts, they hit the reliefs and had to be dremmeled out. Point is, by timing an engine out, with clay, what are you really trying to find that you couldnt find by depressing the valves? I know in some race engines with high lift cams, those valves can travel down faster than the piston can get out of the way. I think in those situations, that would be a good reason to check the engines by claying it up. Dont take it the wrong way, im just asking if there was another think you were looking for by claying the pistons and timing the engine.

mk

mark kibort

It means, going through the effort to put the heads and gaskets on, as welll as installing both sets of cams, timing them, (no small task) installing the timing belt to tension and then, rotating the crank to see if anything hits.

I think this process would be dangerous if you are worried about valve clearances. you have to use a pretty big wrench and rotate the engine, and even a small problem could hurt a valve. that could be detected statically by just claying the pistons and depressing the valves.

Then, the entire assembly has to be disassembled and the clay cleaned off and re-assembled.

John Veninger

I fully understand. Maybe your speaking about yourself in this statement.


yes

So Scott's 5.0L build is non-interference?

yep