HELP please! I tried starting, get loud bank like a big firecracker

[IGeeky1]

Last year this MCM (gm) 4 cyl 3.0L engine ran.

I had engine apart a bit, replaced cylinder head gasket, manifold gasket, carb gasket, fuel pump filter and gasket, water pump and gasket. Replaced starter brushes and put on new solenoid, cleaned wire contacts, put in new gapped plugs.

I did have to remove fuel pump and dizzy. I was careful when I removed the dizzy, took photos, marked lifter cover plate. Made certain not to move pistons while I had it out. I have double checked dizzy position with photo taken prior to removal and it as as close to original position as can be made by this visual.

Stern drive is still off, I tried to start just to see if it would start. Plan was to turn off as soon as it started. The starter cranked for a bit then BANG! loud crack and smoke out of exhaust. I turned off and pulled all plugs and every cylinder was smoking.

Cleaned plugs, checked firing order I think of it as 4 3 1 2 looking at plugs from rear of engine forward. This is just my way of thinking of a 1 3 4 2 firing order. Although I never removed wires from the dizzy cap, I double checked plug location at cap with manual and all is good. Tried again with same result.

 

[Don S]

Re: HELP please! I tried starting, get loud bank like a big firecracker

What are we working on?

 

[IGeeky1]

Re: HELP please! I tried starting, get loud bank like a big firecracker

Sorry, 1989 Mercruiser GM MCM 3.0L 4 cyl engine

 

[IGeeky1]

Re: HELP please! I tried starting, get loud bank like a big firecracker

To me it seems like some sort of timing issue and since I moved both wires and dizzy they seem like likely culprits. They look good to me but wanted to post in the event extra eyes saw something.

What else could be causing this loud firecracker bang? Backfire I'm assuming...

before dizzy pos View attachment 203169
after dizzy pos
after wire pos

 

[IGeeky1]

Re: HELP please! I tried starting, get loud bank like a big firecracker

And the after image rotated to line up and transposed over the before image...

After image is in the red box and has the lifter cover bolts installed




sorry about the attached thumbnail here, I don't know how to kill it.

 

[Don S]

Re: HELP please! I tried starting, get loud bank like a big firecracker

How did you adjust the valves after you replaced the head gasket?

 

[Eric 3.7LX Alpha 1]

Re: HELP please! I tried starting, get loud bank like a big firecracker

I have never tried to pull the dizzy and reinstall it exactly where it was so I have no idea how it will work out. I've always brought the engine to #1 TDC on Compression stroke, and dropped the dizzy so the rotor is at the #1 post on the dizzy cap.

It may work... but I have always been told to bring the engine back to #1. :noidea:

 

[IGeeky1]

Re: HELP please! I tried starting, get loud bank like a big firecracker

How did you adjust the valves after you replaced the head gasket?

I've a feeling I may be in trouble here...I simply reassembled. My manual show s they are hydraulic lifters... Or am I missing your point altogether?

 

[Don S]

Re: HELP please! I tried starting, get loud bank like a big firecracker

I've a feeling I may be in trouble here...I simply reassembled. Are these not hydraulic lifters? Or am I missing your point altogether?

Yes, they are hydraulic, but you still have to adjust them.

Here is how it's done.

View attachment Valve adjust 4 cyl GM.pdf

 

[IGeeky1]

Re: HELP please! I tried starting, get loud bank like a big firecracker

Thanks Don, the only engines I ever had the head off before were Jeep inline 6 and 4s. They just had you keep things in order, reassemble with lube and torque the nut on the rocker arm. No adjustment was even possible.

Thanks for these instructions, they are make much better sense to me than the ones I found in the manual I obviously ignored.

 

[IGeeky1]

Re: HELP please! I tried starting, get loud bank like a big firecracker

Don, that was definitely what was wrong. Now to put on the muffs and set timing.

Thank you!

I'd love to get you a couple beers

 

[ddrieck]

Re: HELP please! I tried starting, get loud bank like a big firecracker

Yes, they are hydraulic, but you still have to adjust them.

Here is how it's done.

View attachment 203178

Don, don't mean to hijack a post but do you have those instructions for a 165 Mercuiser?

 

[Don S]

Re: HELP please! I tried starting, get loud bank like a big firecracker

Don, don't mean to hijack a post but do you have those instructions for a 165 Mercuiser?

Nope, Just use the same info about finding TDC and how not to overtighten the lifters when finding zero slack, then just use the information in the manual.