OMC Stringer Drive to Mercruiser Conversion

[Rich_V174SS]

Ok, did a compression test on this thing. Readings were around 175 psi on all cylinders except the 2 center cylinders #3 & #4 which were around 140 psi. Personally I don't think I need to dismantle this engine yet. When I start it up cold it runs great, it's only after the choke opens around 20 or 30 seconds later it's starts breaking down, missing and backfiring. I don't think it's compression related but think it's either my test ignition coil or a carburetor/fuel problem. I'm going to pick up a new correct coil for it and see what happens. Here's a new video:

[buckz6319]

Ok, did a compression test on this thing. Readings were around 175 psi on all cylinders except the 2 center cylinders #3 & #4 which were around 140 psi. Personally I don't think I need to dismantle this engine yet. When I start it up cold it runs great, it's only after the choke opens around 20 or 30 seconds later it's starts breaking down, missing and backfiring. I don't think it's compression related but think it's either my test ignition coil or a carburetor/fuel problem. I'm going to pick up a new correct coil for it and see what happens. Here's a new video:

sounds a lot better!:)....how is the progress coming along?
subscribed, will enjoy watching you move forward with this project...it's a good feeling when an engine that you have been working on, fires up! puts a big grin on my face every time

[Rich_V174SS]

how is the progress coming along?

I've only had the engine for 2 days. What you just read and watched was posted today so you know just as much as I do at this point. 

Right at the 50 second mark in the video you can hear the engine start to break up. This is what I've got to figure out.

[Plugcheck]

     I realize there is no impeller involved, but I generally do not run marine engines without water, or maybe I just did not see it in the video.   Generally speaking, if the engine stumbles when the choke comes off it is a sign of lean condition, and I've found a good carb rebuild can clean the fuel passages out to restore the flow to correct levels. The idle circuit draws from the main, and the combination of varnish and lowered fuel level combine to run lean.    Hope this helps., Michael. 

[Rich_V174SS]

     I realize there is no impeller involved, but I generally do not run marine engines without water, or maybe I just did not see it in the video.   Generally speaking, if the engine stumbles when the choke comes off it is a sign of lean condition, and I've found a good carb rebuild can clean the fuel passages out to restore the flow to correct levels. The idle circuit draws from the main, and the combination of varnish and lowered fuel level combine to run lean.    Hope this helps., Michael.

You are correct on all points. I didn't have water running but I wasn't running the engine for more than a minute or so and the engine didn't even get warm. If the new ignition coil doesn't fix the problem I will be going through the carburetor next. This engine had been sitting for quite a few years in a garage so I don't doubt there's going to be some corrosion buildup in the carb.

[Plugcheck]

      I have found engines placed in storage are the worst for developing the varnish since rarely does anyone ready an engine for storage properly.   The fuel was likely left in the bowl, evaporated, and now the main jets have the "film" on them.   Could just pull the top, check the fuel bowl, and give a few squirts of carb cleaner to the mains.   Also gives a chance to see the actual fuel level since it has a profound effect on the fuel mixture.  Granted worse in some models than others.   Otherwise the engine seems to run well, if no leaks I would consider it a keeper and install it.

[Rich_V174SS]

I'm with you on everything, that's my plan. But I don't trust the exhaust manifolds so I'm going to pull them off and check them out thoroughly.

[Plugcheck]

      What is wrong with them?  Not too familiar with marine exhaust, but do they corrode out, or do the gaskets wear out and leak.  I guess I always figured they were cast iron so they last nearly forever?

[Rich_V174SS]

Cast iron exhaust manifolds last on average 5-10 years, less when used in salt water environments because they rust and plug up internally choking off the water flow which can cause engine overheating. Also, the joint where the riser sits on top of the manifold tends to corrode through and you can get water leaking through the joint from the water jacket passages back down into the exhaust ports, the engine can ingest the water into the cylinders - not a good thing.

When I first started up the engine the other night lots of large chunks of rusted iron shavings came blowing out with the exhaust so I need to make sure the water jacket in the manifolds is not rotted through. Hence the reason for not running water through the engine at this time.

[Rich_V174SS]

Additional video below. In this video you can hear the engine starts off smooth but begins to break up at around the 5 second mark, backfires and gets worse until it stalls. I'll be picking up a carburetor kit to rebuild the carb.

[Rich_V174SS]

This arrived today from UPS. Snagged it from ebay for $300 plus shipping and it looks practically brand new, taken from an 80's freshwater boat. This transom assembly looks nicer than the one I used on my V174. It's going to replace the beat up one that I got with the engine for my conversion project.

[Jason]

nice! Even came with the $3 stainless nuts!

[Rich_V174SS]

It even came with the hardware to bolt it through the transom.

[Rich_V174SS]

It feels like spring is here, progress to report ...
Made up a cardboard template for the transom filler. Then cut out the piece of 3/4ths marine ply, trimmed and adjusted to fit. Splattered on some laminating resin, a few strips of glass mat, more resin, then clamped it in place. Will let it sit for about a week for it to fully set.

[Rich_V174SS]

Work resumes now that it is spring time. Winter didn't go exactly as planned.
I've removed the outside clamping board showing the inset plywood sealing up the hole. On the inside I began to do some grinding and made up a template for the second piece of wood that will be glassed to the transom.

[Rosscoe]

Looking good Rich.
Second piece? To get correct thickness, or are you overlaying the seem with another piece?

[Rich_V174SS]

Looking good Rich.
Second piece? To get correct thickness, or are you overlaying the seem with another piece?

Yes to give me the required 2 inch thickness to the transom for the Mercruiser assembly, and yes the second piece will be larger than the first to overlay the seam.

[Plugcheck]

      Looks like you do some fine work.   Kinda curious, will you build up the outside with cloth and resin to make the outside surface smooth or use some type of filler?   Just wondering how you cover the edge between the old and new areas and get it smooth.   Since my Z was Mercruiser before, I don't have the same issue.

[Rich_V174SS]

The outside will be layered with fiberglass to fill the hole so the surface is flush with the surrounding transom, sanded smooth and flat, gelcoated and then the hole will be recut for the Mercruiser. After I'm done you shouldn't be able to tell there was an OMC hole there.

[akaV153]

Lookin good Rich. Glad someone's making progress ...