Rebuilt my m20 and oops???

[Bmr]

Almost looks like the timing belt jumped or the gear moved judging by the marks in the other piston(the one without the hole)
Timing belt was in the same spot as it was. I made sure everything was good. Triple checked all my timing.
sucks man

From valves touching pistons

"Had the head decked just below max clearance" + "Put my nice shrick 288 cam cam in" = "Carnage!!!!"

That is a big cam and would need the piston to valve clearance checked ;)

schrick 288 has about 1.5mm to 2mm additional lift at TDC and just eitherside compared to stock, there is a reason why certain members always recomend checking PtoV clearance..........

With a thicker head gasket and the cam adjusted with the cam gear i was sure valve clearance was good. I had checked out of car and valves lined up perfect. Like i said i triple checked.

Since the engine ran fine for a while, my guess is that your adjustable cam sprocket moved. Which is something I've seen happen before. I won't use one and if cam timing needs to be adjusted I'll make an eccentric bushing to go into the cam sprocket. There is no way that can slip.

^ I got the cam gear online and honestly I think its a pile of crap now that i look at it.

could also be that it was so close that as things loosened up, timing belt stretched a little under load, even a lack of valve control caused a kiss, tipped it over the edge.

Did the OP check PtoV? what valve springs?

If you didn't check valve- to- piston clearance, that'd be my vote-

they CAN kiss for a while, then... well, my condolences, anyway, that sucks.

t

I don't know where you got those numbers, but they are way too big. If you deck the head to the max (bottom of the limit dimples) offsetting the cam sprocket index pin 3/16" will bring the cam back into time. That is way, way, less than 20deg.

I had the cam adjusted 5% degrees. That's about 3/16

[e30trooper]

I don't know where you got those numbers, but they are way too big. If you deck the head to the max (bottom of the limit dimples) offsetting the cam sprocket index pin 3/16" will bring the cam back into time. That is way, way, less than 20deg.

http://www.e30tech.com/forum/showthread.php?t=110839

this goes for eta block with a decked 885 head.

[nando]

did you *measure* the valve clearance?

lining up the cam spocket doesn't matter. even if the head hadn't been decked, it's likely the 288 would have had valve clearance issues.

the first thing I thought of before I read the 2nd post from the OP, was that he hadn't measured PtV clearance and his engine blew up. :(

[Bmr]

did you *measure* the valve clearance?

lining up the cam spocket doesn't matter. even if the head hadn't been decked, it's likely the 288 would have had valve clearance issues.

the first thing I thought of before I read the 2nd post from the OP, was that he hadn't measured PtV clearance and his engine blew up. :(

I did not check with that putty crap or whatever its called. I turned it manual and inspected each cylinder. The car ran fine for 2 days straight.

[etxxz]

thoughts from an engine designer.

No other piston made contact with the valves suggest it wasn't either the surfaced head or the thickness of the head gasket.

If timing had moved, i can almost guarantee you would have seen another piston at minimum kiss the valves ie. cyl 3 or 4 (can't see exactly which - whichever goes up at the same time). I say something let go. How are the valve hats/retainers for that cyl?

When you mess with an engine this much, i take no chances and use a timing wheel to degree the engine with gauges the old school way. I'm sure the manufacturer also gives you the appropriate max lift at engine degree spec for that camshaft. Time the engine that way. Second. measure PtV using a weak spring in place and the gauge as you rotate the engine. Closest encounter will be well after TDC as the intake valves enters the camshaft ramp. You want to be min 1.5-2mm away at the worst Anyways. That's why there are engine builders and driveway mechanics. I was the latter for many years and have also broken an engine because i didnt know what i know now. Live and learn, i wish i could have given you some input before.

[Bmr]

thoughts from an engine designer.

No other piston made contact with the valves suggest it wasn't either the surfaced head or the thickness of the head gasket.

If timing had moved, i can almost guarantee you would have seen another piston at minimum kiss the valves ie. cyl 3 or 4 (can't see exactly which - whichever goes up at the same time). I say something let go. How are the valve hats/retainers for that cyl?

When you mess with an engine this much, i take no chances and use a timing wheel to degree the engine with gauges the old school way. I'm sure the manufacturer also gives you the appropriate max lift at engine degree spec for that camshaft. Time the engine that way. Second. measure PtV using a weak spring in place and the gauge as you rotate the engine. Closest encounter will be well after TDC as the intake valves enters the camshaft ramp. You want to be min 1.5-2mm away at the worst Anyways. That's why there are engine builders and driveway mechanics. I was the latter for many years and have also broken an engine because i didnt know what i know now. Live and learn, i wish i could have given you some input before.

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?

[Bmr]

ill take a picture of the valves on that cylinder.

[jlevie]

http://www.e30tech.com/forum/showthread.php?t=110839

this goes for eta block with a decked 885 head.

I looked all through that thread and didn't see anything to support your assertion. The one calculation I did see (on the first page) is wrong.

If you move the head 0.010" closer to the crank center line the load side of the belt needs to be 0.010" less to retain correct cam timing. Which means the cam needs to be retarded so that the load side of the belt distance is correct.

The cam sprocket is darn close to 4.875, which means it's circumference is 15.31". Retarding the cam to make the load path 0.010" longer is .00644 of the circumference. Multiply that by 360deg and you get 2.32deg.

[Bmr]

this broke, would it make the valve hit? one cylinder is damaged, rest are fine.

[Bmr]

well..

[digger]

it probably broke on the impact when the piston smashed into the valve

[jeffnhiscars]

it probably broke on the impact when the piston smashed into the valve

^^ Once your rocker broke I dont see how the valve is going to hit anything since it cant move.

[nando]

I did not check with that putty crap or whatever its called. I turned it manual and inspected each cylinder. The car ran fine for 2 days straight.

I use a dial indicator and a flathead screwdriver to compress the valve (in the fork of the rocker).

if you didn't measure, you don't know, and I do know that the intake valve on the 288 has some pretty agressive lift at TDC. 99% chance that is your problem.

it ran fine because it probably had a tiny amount of clearance. that's why rotating it by hand is totally meaningless. minimum clearance is 1.5mm, if you had even 1.0 mm, it's not enough because as things heat up they expand, and that clearance lessens. Eventually whatever valve was weakest (or touching more due to slightly different clearance) fails and your engine explodes.

you wouldn't be the first person who had their engine "run fine" for a day or so and then suddenly explode, and you probably won't be the last.

[nando]

^^ Once your rocker broke I dont see how the valve is going to hit anything since it cant move.

if the valve is bent it's not going to close all the way and will still hit the piston, several thousand times a minute.

[Bmr]

I use a dial indicator and a flathead screwdriver to compress the valve (in the fork of the rocker).

if you didn't measure, you don't know, and I do know that the intake valve on the 288 has some pretty agressive lift at TDC. 99% chance that is your problem.

it ran fine because it probably had a tiny amount of clearance. that's why rotating it by hand is totally meaningless. minimum clearance is 1.5mm, if you had even 1.0 mm, it's not enough because as things heat up they expand, and that clearance lessens. Eventually whatever valve was weakest (or touching more due to slightly different clearance) fails and your engine explodes.

you wouldn't be the first person who had their engine "run fine" for a day or so and then suddenly explode, and you probably won't be the last.

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. shrick specs the cam lift is 7,3 and 11, 4 valve lift. valve clearance is 0,25 intake and exhaust. Head gasket thickness is .070 and with 18 thousand taken off from stock head height. Well within the limits of valve clearance.