1990 OMC 4.3L No-Start Condition :*(

[franklynwsmith]

Morning,
I recently just purchased a 1991 Sunbird Corsair 185 boat. Has a 1990 OMC 4.3L on it (I paid almost nothing for the boat).
It came with a ton of different problems, which should be expected on a super cheap thing.
Took me a while to get wiring all fixed up and working and then tried starting the engine and had no-starts due to bad heads (blown head gaskets and stuck-open valves)

I've never actually dealt with a pushrod motor before. Which caused "lots of fun" when I torqued down the rocker arms.... lol.... Had to untorque them and try to get them back up to the procedure I later found.
But I am getting mixed answers on whether or not the pushrods are all the same length. Some places have said the intakes are slightly longer, some are saying they are the same length.
Does anyone know?
Or could I have just done the rocker arms incorrectly again?
A few of the cylinders are showing 30PSI on a compression test, and 25ish with a cylinder leakdown test (and sounds like air escaping the exhaust valve)

Thanks a ton!

Franklyn

 

[Scott Danforth]

first, welcome aboard

next, step back and put the wrench down

yes, all the pushrods are the same length. and you set the valvetrain by 1/2 to 3/4 turn past zero lash. zero lash is zero up-down movement by your two fingers, not the zero ability to spin the pushrod. you only want to collapse the lifter spring by about 0.050"

follow the GM manual procedure on this. if you have a haynes, Chilton, or Seloc manual. use that as knee pads or toilet paper and get a proper GM or OMC manual. https://outboardbooks.com/

after properly setting the valves, with any cylinders below 120 psi, you have a rebuilder.

head gaskets do not just blow and valve do not just rust on their own. they are murdered. most likely the one piece exhaust manifolds have failed and rusted the valves and cylinders and taken out the motor

@Lou C has a good writeup on updating the exhaust.

also, you will need to service your points long before trying to start

 

[Lou C]

Yep I did that same job, replaced heads in 2017, I had an overheat in 2013 which I'm sure damaged the head gaskets, they finally leaked in '16, but looking back I saw some salt water showing the oil sample as far back as 2011, so they had already started to leak before the overheat. Had water in one cyl just a mist of water in the other.
Pushrods are all the same size. You really need to follow GM's procedure for setting the hydraulic lash adjusters, it is a little confusing if you have never done it before, and if you've tightened them too much that can definitely lower your compression test results.
At the same time I converted mine from the batwings to the conventional 2 piece units, I used a Barr Aftermarket kit & bought Volvo Penta OEM 90* down pipes and rubber exhaust hoses. A little pricey because it was VP OEM but everything fit right and no leaks. I just checked the inside of the manifold/elbow joint with my inspection camera (fits right in the port on the top of the elbow, that is actually for an exhaust overheat alarm but comes with a square plug in it). I do this each fall now so I can see if they are not leaking inside or, if it's time for new exhaust.
I never had water in the motor from the batwings, in fact when I first got water in a cylinder I thought it was that, but tested them and nope, not that simple lol. I changed over to the 2 piece because those had 6 years in salt already on them. I do think from what I could see, that the wall thickness is better on the Barr units. So if you want it to last, a good idea.

 

[Lou C]

looks pretty good.

you can see the pipe plugs I used to do the inspection on the top of the elbows, there are also larger plugs on the sides that can be used for the same purpose. Those are for a type of vacuum break set up that they adopted after they came out with the Vortec engines due to there being more vacuum in the exhaust, they used a one way valve that let air into the exhaust but didn't let it escape, this helped in keeping water from climbing up the 90* down pipe. It wasn't necessary on the pre-vortec that I have.

look at the difference in the wall thickness from the Barr manifolds, and the outlet of the batwings.....