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Post by stepthrutuner on Jan 19, 2012 23:29:04 GMT -5
I went with a guy (Steve) I work with who is an experienced auto mechanic to look at a 150 hp 2.5l v6 Mariner outboard boat motor that had a seized #6 piston. We think the seizure was caused by a weak mixture from one side of the supplying dual venturi carb. The owner was quoted a repair price of $5000 which he thought was rather outrageous and decided to do the teardown and reassembly of the motor himself with the help of Steve. I just went along to see the innards of a V6 2t and offer a little insight into 2 strokes since Steve's experience was with four strokes. My curiosity was piqued by the shape and configuration of the exhaust ports. The shaded red area was a planar member approximately 3/16" thick that ran the length of each bank and appeared to be immovable to my cursory inspection. I first thought power valve but on finding the member immovable as far as I could tell I am at a loss to explain this configuration. Can anyone shed some light on what the setup is? The member in question is just a little ways (1/8" or so) from the cylinder wall inside the exhaust port. Attachments:
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Post by 90GTVert on Jan 20, 2012 12:43:43 GMT -5
It's a shame lauderdaleboats isn't around lately. I sure have no clue what that would be if it's really unable to move.
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Post by jmkjr72 on Jan 20, 2012 15:30:38 GMT -5
ive got a 2 stroke boat engine but i have never had to realy do any work on it
it needs some carb work before it can go out agian but i couldnt tell you anything about the insides
but mine is also a 70s johnson 150hp 4cyl
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Post by stepthrutuner on Jan 20, 2012 21:21:23 GMT -5
It almost has to be a movable power valve. I just didn't see the actuator. Yeah, laderdaleboats woulda known for sure. Sure wish he was still around I was looking forward to his build.
Each crank chamber is isolated from it's neighbor by a large piston ring looking highly polished isolator that compresses when the crank cradle is bolted on. Circular plates with grooves for the trapped rings are spaced along the crank. The rings, of course, stay stationary while the plates revolve. The intake manifold is bolted to the crank cradle cradle. On the other end the exhaust ports dump into a manifold in the interior of the vee and there is an upright 'wall' (I don't think it exactly completely isolates each bank from the other but keeps the high pressure exhaust pulses from shooting directly across to the other bank) down the middle of the length of the exhaust manifold.
The connecting rods had capped bottom ends and the roller bearings there had split plastic cages.
The 2t oil (at least part of it) is injected into a transfer port of each cylinder.
Seeing the intricate crank, etc. it's not hard to see why these things cost so much and last so long.
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Post by stepthrutuner on Jan 20, 2012 21:42:14 GMT -5
The underside of the intake manifold had reed valves for each throat (stainless.... one was chipped)
The piston tops were lightly dished but flat across the dished area. The combustion chambers were inverted pie pan shaped (trapizoidal) and were pretty deep (over 1/2 inch as I remember).
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Post by stepthrutuner on Jan 28, 2012 0:26:11 GMT -5
Well, I don't know where I got the idea that the piston tops were slightly dished. They are, in fact, flat as you can see from the picture of the damaged piston. It happens the owner of the motor is named Steve also and I found out that his sister used to be married to one of my third cousins who have the same last name as me. I went over to see him tonight and learn a little more about marine outboard 2t motors. Things I learned tonight and by doing a little research on the net and from a repair manual that Steve bought: The fuel pump is a pulse type and gets it's diaphragm actuation from cyl. # 6 (lowest) crank chamber. There is a fuel/oil scavenging system that recirculates that fluid from recesses machined at the lowest points of each crank chamber. Through a system of tubing the mixture is forced under primary compression through a check valve and then dumped in the transfer ports of all the cylinders. This is necessary due to the sluggish movement of air/fuel/oil at idle speeds.  The infamous piston and newly sleeved cylinder to the rt.^  The even numbered bank. I believe the newly sleeved cyl. is on the left.^  The curiously shaped ex. prts. I've yet to figure out.^ Note the mar to the rt. of the ex. prt. where the rebuild shop person let his burr slip while chamfering the prt. Unfortunate but inconsequential probably.  The ex. manifold with central separating wall that fits within the vee.^  Intake manifold. I'll be aiding in reassembly early next week probably. Try to get more pic. |
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Post by 90GTVert on Jan 28, 2012 0:39:03 GMT -5
Thanks for the pics and info Reg.
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Post by 190mech on Jan 28, 2012 6:19:29 GMT -5
Possibly a "compression release"?I know some of the big MX bikes have a hole drilled drilled above the Ex port to relieve starting compression a bit...
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Post by stepthrutuner on Jan 28, 2012 8:42:28 GMT -5
Possibly. I'll do some more searching.
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