Did I hit a valve?

[souljah702]

I have been coming here for all of my inquiries about my J30s. You guys have saved me plenty of times. Im really hoping you can help me with this one. So I started by changing the water pump, for some odd reason the crankshaft drive did not line up but the other 4 sprockets did. Im thinking it slipped during my attempt to take the bolt off of the crank pulley. I checked the fsm manual and that wasnt right but i was weirded out because the belt was never taken off. ANd the car ran fine before so i took a chance and left it and put it all together. Bad idea? I cranked it and it didnt start, i didnt hear anything like the pistons hitting the valves but i took it all apart again and then lined everything up and put a new belt but the cams did move around when the belt wasnt on, lined it all up then tried again . Nothing! Thats when i got scared. Number 1 piston has no compression so im thinking im screwed. So my next step is to take apart the engine and buy and reseat the valves. Thank god my next door neighbor is a machinist and does 30+ heads a day and can handle the head and valve part and what not. My question to you guys is if its possible that the notch on the oil pump housing and the gear match up. Is it always on tdc compression or is there a chance its on tdc exhaust. If so, if i turn the crank gear 360 with out turning the others will that put it on compression. If there is no other option available, then imma start tearing it apart. But do you know where to find the info on how to take the intake manifold off cuz that sucker looks complicated. I know i can figure it out but im trying to cut time. Please help, all of your time is greatly appreciated. Thanks guys

[fogged306]

I'm more of a pushrod guy so as far as timing a OHC motor, I'm not the best to answer that.

I can tell you though, that yes there is a TDC on exhaust and on compression, you want the TDC on the compression stroke. No compression in cylinder no. 1 after leaving the cams loose like that is an indicator of incorrect timing. If you are a couple teeth off on the belt, the valve could be open now when it's supposed to be closed for the compression stroke and it will lead to a no compression situation.

[GerryO]

If so, if i turn the crank gear 360 with out turning the others will that put it on compression. If there is no other option available, then imma start tearing it apart. But do you know where to find the info on how to take the intake manifold off cuz that sucker looks complicated. I know i can figure it out but im trying to cut time. Please help, all of your time is greatly appreciated. Thanks guys

My gut feeling is to stay far away from this one. Turning the crank 360 just brings the pistons back to where they all started. The same for any of the four camshafts turned 360 deg. It's how they are all connected together and the timing of everything that's important. At TDC for a particular cylinder all the intake and exhaust valves are closed, causing compression of the air/fuel mixture and creating the proper time to spark/ignite it in order to force/power the piston downward. It's a four cycle engine, so the are the intake, compression, power and exhaust strokes for each cylinder. The interlocking piston driven crank and valve driven camshaft positions determine them for each cylinder, all in the repeating firing order sequence.

http://en.wikipedia.org/wiki/Four-stroke_cycle

Notice that the intake valve is open (closer to the piston top) when the piston is traveling downward during the intake stroke and that the exhaust valve is open (closer to the piston top) when the piston is moving upward during the exhaust stoke.

I don't know if you stand to loose much by just putting the timing belt back on correctly and first turning the engine over by hand and then cranking it with the starter to perform a wet compression test, provided things turn freely/quietly by hand.

I suppose you could try positioning a cylinder at TDC and gently turning/not forcing intake and exhaust camshafts in order just contact a valve with a piston top, just to get the feel of it. Maybe do it to a Z32 engine in a local wrecking yard? I really don't know how much interference there is between valves and the piston tops, but any amount of contact in a running engine would probably bend a valve and damage a piston top.

Or maybe you could do some sort of static leak-down test (a pump and gauge connected via the threaded spark plug hole) on each cylinder at TDC with the timing belt properly connected, that would tell you the general condition of the rings and valves for each cylinder.

Good luck.
Modified by GerryO at 6:14 PM 9/18/2008