[Rossco]

Just replaced the head on a g16b because the old one was cracked. I bought the whole top end (head and intake manifold) of the engine which I was told was reconditioned and looked clean. It was a straight swap to put it on, I only changed the head gasket.

Now, I can't get it to fire up. It has spark, fuel and air. The timing is correct, it has been triple checked by a mechanic. Just did a compression test and all 4 cylinders are at 90 psi. Is there anything I could be missing? And it my next move to take it back off and get it to a reconditioners?

[Scrawny]

I bet the timing is 180 degrees out

[Rossco]

negatory we have tried it both ways

[Scrawny]

Did you have the head gasket surface machined?

[Rossco]

I didn't, and this is where we think the problem is now. The head however looked reconditioned but I cant say if it had been machined. Loosing almost 100psi seems like a lot though for something that might only be off a few thousands of an inch.

[droverdave]

Put a teaspoon of oil down each cylinder and test it again.

[JrZook]

Since a new head was put on a previously running engine the rings etc should be good. For it to be down 100psi evenly across all 4 pots there has to be a common issue.

What alignment hole did you use on the camshaft sprocket? The I or the E? If you use the wrong one the cam timing will be wayy off causing a compression loss.

[Rossco]

Crank was at TDC and we used the E.

Could be valves not seating properly but everything looks new.

[JrZook]

Valve clearances set to spec?

[Rossco]

I haven't checked them, could that cause seating problems?

[JrZook]

Yup. If there is no clearance they will not close/seat completely and leak

[Rossco]

There is some valve lash because we check that all of the valves were closed at TDC on all cylinders. This would suggest that the valves were closing all of the way right?

[watermouse]

The valves might all be closed at TDC for each cylinder but is the inlet valve closing at BDC or slightly afterwards? If it is after you are pushing the charge back out, losing psi.
Check timing pulleys are mounted to cam and crank in the right spot. No slop on cam pulley?

[Rossco]

valves are operating as they should and I have set all of the clearances. Timing belt and cam pulley are good as well. I'm thinking its the valves not seating properly so its going to the machine shop this week.

[JrZook]

Be a pretty epic coincidence that every valve is not seated as such to get an even 90psi across all 4 cylinders. Headbolts not bottoming out by any chance?

[Rossco]

I know, it would be hey. well the head bolts I got from 4wd products were torx head. They started to round around 65nm and they should be done up to 70-75nm. I think it would still be a coincidence if the head wasn't torqued exactly to specification, that all the cylinders would have the same low compression within 5 psi.

[JrZook]

Its very odd what ever it is. Still seems to point to cam timing to have such an even loss over all 4. Be interesting to see what you find as the actual cause.

Was the comp test done at WOT?

[Rossco]

yup the accelerator pedal was depressed. I keep coming back to cam timing as well but I know the crank was at tdc and the e was at 12 o'clock on the cam pulley. Also all of the valves on cylinder 4 are closed at TDC which would support that it is done correctly. I'll talk to the engine shop tomorrow and maybe pull the timing cover off again to have another look.

[JrZook]

So I'm assuming you used the "E" slot on the pulley to position the cam dowel pin and used the "E" mark on the cam pulley to set the timing?

The cam has a heap of dwell when the rockers are on "the rock" so the assumption that the valve timing is correct because they are closed at TDC is not definitive. Thus, you could still have the valves closed on TDC with the inlet valve closing late and have a lot of the charge escaping back out the intake on the compression stroke, dropping the dynamic cranking compression pressure.

[royce]

can you do a compression test on another engine? make sure your gauge isnt stuffed and making you miss another problem

[Rossco]

Here is how I aligned the timing belt, not my engine but identical to what I did.





Interesting thought Royce I can tomorrow. However I will also add that we had a mechanic come round to help us with the timing and when we couldn't get it started. He commented that air wasn't "popping" out of the spark plug holes like an engine under compression does. He then lent us his compression tester and we found 90psi.

[Rossco]

ok had another go at it today and I still cant get it started. The cam timing is spot on now as per the pic below and the dizzy should be done correctly. We put it on number 1 and got it to 6 degrees BTDC with a timing light and then swapped it 180 degrees when that didn't fire. Neither position gave even a cough. There is a strong spark, fuel, and air. I don't understand how this motor wont even sputter when it drove in, the timing is correct, and it has fuel and spark.

quick side note, I humored myself and put a bit of oil down the cylinder, compression was 110 after that. I'm assuming that if I could get the engine warm it would be much closer to the 170 it is supposed to be.

I am completely out of ideas here, I am tired of dealing with this and I need my car back. Any other ideas before this gets put on a tilt tray to the mechanics?

[monley]

May sound like a stupid question, but what condition are your spark plugs in? Do they have the correct gap?

[JrZook]

That compression is quite concerning. I highly doubt that you would get anywhere near 170 warm. For reference my g16b with ~150k on it pulls just under 200psi cold.

So how did the engine run prior to the head swap? Burn much oil? Low on power? With ~100psi in all 4's it would barely run.

[jdk81]

You may need to pull the head again.
check the valves, gasket, bolts, etc
Possibly get the head pressure tested


Possible scenarios I can think of which havent been mentioned.

valve seats were cut and then head was partially assembled, and someone forgot to lap the valves and fully assembled it.

valve seats cut at wrong angle
Different valves, but assumed close enough..

[Rossco]

Plugs are brand newies, I have never seen such a good spark. The engine ran fine. It didnt burn oil ever but it dd seem a bit down on power. I attributed this to the cracked head, and I was taking it easy to avoid heating things up to much. In the end I agree with you jdk and jr. The compression is a problem and seeing as the cam timing is now correct I think it is time for the head to come off. My fault for assuming it would be alright and not having anyone look at it before I put it in.

[royce]

did you over heat it before you swapped heads?

squirt some carby clean in the throttle body and see if it will cough

[jdk81]

Aerostart down the tb while cranking?

[Rossco]

I never had boiling fluid but it did go to the top third of the temperature gauge. I know these aren't accurate but relative the the bottom third it used to stay in, it was above normal operating temperature. I pumped it full of "start fuck ya", didn't even cough. This is puzzling because I assume it would do at least something, even with low compression.

[droverdave]

Do you have a leak down test tool? That might help in diagnosing where the compression is going.

Not being an expert on g16 engines, is it at all possible you have the wrong head and piston combination? ie the head you have has more chamber volume compared to what you had and causing lower compression?