Rebuilt my m20 and oops???

[nando]

okay, you're the one who didn't check it :p

as I said, rotating the engine by hand means nothing. it will clear with .5mm of PTV clearance but that is definitely not enough for a running engine. and yes one could fail before the others. since it ran fine for 2 days, you know it was very close.

where you at in bham?

I *really* doubt the spring failed.

[brianao34]

Still doesn't make sense. So your saying one cylinder failed because of clearance. I call BS, if your up here in bham come by and take a look. I think the spring failed, because that makes sense. It compressed and didn't return fast enough. But heh you guys can have your valve clearance fantasy stories. :P

Ha. Let's see that spring then

[Bmr]

okay, you're the one who didn't check it :p

as I said, rotating the engine by hand means nothing. it will clear with .5mm of PTV clearance but that is definitely not enough for a running engine. and yes one could fail before the others. since it ran fine for 2 days, you know it was very close.

where you at in bham?

I *really* doubt the spring failed.

Off elm street right down the road from the restore. I m just giving you guys shit honestly. If that's what it that's what it is. Rather than people just spew out random facts without backing it up makes me laugh. I would assume you have way more experience than me so i wasn't saying your wrong. Just want to make sure this doesn't happen again, lol.

[nando]

I do have experience directly with this. However, I got extremely lucky. my PTV clearance with my stock bottom end and the schrick 284 was right at the minimum (maybe slightly under). the valves were so close to touching the pistons that the carbon deposits were cleaned out of the valve pockets when I took it apart, but there was no metal/metal contact and nothing was damaged after ~15,000 miles or so. With even .1mm less clearance I'm sure it would have broken something.

[whodwho]

Also you may not feel any interference when rotating the engine even if there were touching as you have some leverage with the crank/cam ratio.

[BavBeater85]

so this was in no way caused by a loose or bad rod bearing? I had a 2.3 stroker turboed eclipse that at one time had the main rod bearing replaced, but none of the others...two months after i bought it the main rod bearing went (presumably due to different bearing clearances) and the number one piston kissed the valves, and bye bye expensive stroker

[structured]

Did you use stock springs with that cam? It could be a combination of what Nando is saying (not enough clearance) and the spring not being able to return the valve back to the seat in time. In other words, the valve is floating back to seat rather than riding the cam lobe. The floating issue is something which you can never tell by turning the engine by hand, but it can greatly reduce valve clearance while the engine is rotating. Stock strings are not good enough for such a high lift (and fast lifting) cam.

I had a 228 in my Seta "stroker" and I could rotate the engine fine by hand. When I finally measured, though, I found out that the valves were actually touching the pistons. I ended up swapping the cam for a 272.

Here is a post showing the clearance on my engine. I know that it is not the same as yours...

http://www.r3vlimited.com/board/showpost.php?p=2859806&postcount=1

[Bmr]

Did you use stock springs with that cam? It could be a combination of what Nando is saying (not enough clearance) and the spring not being able to return the valve back to the seat in time. In other words, the valve is floating back to seat rather than riding the cam lobe. The floating issue is something which you can never tell by turning the engine by hand, but it can greatly reduce valve clearance while the engine is rotating. Stock strings are not good enough for such a high lift (and fast lifting) cam.

I had a 228 in my Seta "stroker" and I could rotate the engine fine by hand. When I finally measured, though, I found out that the valves were actually touching the pistons. I ended up swapping the cam for a 272.

Here is a post showing the clearance on my engine. I know that it is not the same as yours...

http://www.r3vlimited.com/board/show...06&postcount=1

Where did you find that graph for clearance?^

I contacted shrick via vac motorsports about this and asked them over the phone told them what my car does and what rpms it runs at. They specifically told me only to get the springs if and only if i use this car for road race were its at high rpms all the time. The tech i talked to said for a street car and auto-x I wouldn't need to worry about and to make sure the timing was dialed in with a adjustable cam gear. He also told me they built many successful 288 cam e30s running on the street. same as my application with a head decked. So to answer your question yes they were new stock springs. When i checked the compression I was at 175 to 180 all the way across also.

[structured]

I made both graphs. The second one was made by measuring the actual clearance between my valves and pistons and plotting that against the crank rotation relative to TDC.

Your car would not have the same chart because your crank is shorter and the cam would never be in the exact same place. I just posted it to show how you would check the clearance correctly. Valve clearance depends on a lot of variables. It really needs to be checked when using such a big cam.

This may not have been your problem, but it certainly looks possible.

[Bmr]

I made both graphs. The second one was made by measuring the actual clearance between my valves and pistons and plotting that against the crank position relative to TDC.

Your car would not have the same chart because your crank is shorter and the cam would never be in the exact same place. I just posted it to show how you would check the clearance correctly.

Makes sense. What exactly did you go with then after selling the cam?

[etxxz]

Oh boy that picture of the rocker changes things.

I don't think clearance was the reason for the engine failure. First thing i mentioned in my previous post. What do your valve springs hats and collets look like for that cyl?

[Bmr]

Oh boy that picture of the rocker changes things.

I don't think clearance was the reason for the engine failure. First thing i mentioned in my previous post. What do your valve springs hats and collets look like for that cyl?

That pic shows it. I will try and take it off tonight

[CarsSuck]

Have you seen the build threads by Raxe and Accolella? You should definitely check BulletRide's, page 4/

[etxxz]

Damn, thank you, this makes sense now. Well the cam is still good so im putting it in another head and doing this. when you say 1.5 to 2mm you mean from piston?

and to clarify your question about PtV clearance.

You're at TDC, put the dial gauge on the valve hat, push down valve (this is why i use weak springs) till the valve touches the piston. That distance the valve moved is your PtV clearance. Turn engine a few degrees. Repeat. That's how you GRAPH your piston clearance as a function of crank angle. Doing one intake and one exhaust valve is all you need to do really.

The graph from cam manufacturer with the lift profile is how you time the engine. You find TDC with a degree wheel. Match max lift with the degree spec'd is the best way to time the engine.

You must first "FIND" TDC with the gauge through the spark plug hole riding on the piston. I normally measure 0.50mm lift before and after TDC and calcualte on the degree wheel where the middle, or zero (TDC) really is. Remember that near TDC, the piston doesnt move much up and down so its hard to find, you can be like 10 degrees off this way.

Anyways, plz pm me a lot when you put this sucka back together. i'd be glad to give you a hand with anything technical.


*waiting for analysis on the valve train for those valves... or am i looking at the valve stems still on the springs???

[structured]

Makes sense. What exactly did you go with then after selling the cam?

I never actually sold the cam. Not sure why, but nobody seems to want it. Right now I am running a generic 272 (similar to what Ireland Engineering sells I think).