1977 115HP V4, comp tests 125psi, 120psi, 115psi and Eeek! 50psi

[Greg Boswell]

First of summer after having sorted out my link and sync, I was happily running around the bay for days and weeks. One evening on a glass smooth bay, I hit something submerged at full speed. I believe it had to be a fish, a fairly large one because I never saw anything surface. It put a little ding on one prop blade, but otherwise I found no damage like I hit something solid, over 6 feet deep where I was as I put the paddle over the side to see if I hit shallow sand bar maybe, but nothing.

Anyway, the hit also caused my trim and tilt to crack the Tee fitting on starboard, so that got both of them pulled and cleaned and painted.

**Here is the problem** Now, this past weekend I'm seeing a little difficulty starting and some odd vibration at mid throttle, not really putting out full power, but still getting up on a plane and moves on.

Tonight, I do a compression test and get 120psi to 125psi on the starboard cylinders and 115psi and 50psi on the port cylinders. Last time I had pretty much all 125psi when I tested.

I borrowed an inspection camera and looked inside all 4 cylinders through the plug holes and all looked nice and clean, very little carbon, and most importantly, no hole in the low pressure cylinder.

I thought I might have a twisted crank, but it appears all four pistons are coming up tdc when they should.

Anyone have some other possibilities or thoughts on what I can check. Maybe do a leak down pressure test or it that feasible with a 2-stroke.

Thanks in advance.

Sincerely,
Greg

 

[F_R]

Whatever it is, it isn't going away by itself, so you might as well start searching. I'd pull the head first. May be a blown head gasket. If not, you probably can see what came loose. Surprising you couldn't see it with the scope though. You can also pull the intake and exhaust covers. Certainly you will have found it by then.

The whole story seems kind of unlikely. I can't think of any reason hitting something should cause loss of compression. I suppose you are sure there isn't some weird reason you are getting a bad test (?)

 

[Greg Boswell]

That was the last run of the day and I figured it was worth mentioning. It was running on all four at full speed.
Whatever I ran over caused the boat to come to an abrupt stop and it dented one blade of my prop, but no paint loss on a black aluminum prop, the outdrive came up, either the pressure on the Trim and Tilt or just age caused the hydraulic tee fitting to bust open and motor would not start back up right away. I did get it started up eventually, figuring the temp sensor had kicked in or a combo of instant shut down and speeding caused temps to kick in the auto stop feature. But, it was stumbling and idle was off, would die when put into gear. This was making me think I had twisted the crank assembly. I also found I had a couple of bad coils which was part of the reason it was hard to start back up I suppose. New coils, fresh plugs, checked link and sync, but did not think to check compression until today.

For sure, something weird is going on. Can a bad reed valve cause a low compression reading. The cylinder above the 50psi is down to 115psi from a prior reading of 125 psi. Both right (port) banks cylinders are within 5psi and still at or over 120psi. What would checking the exhaust side do?
I also figured I'd see some tell tale evidence of low compression with the camera, but granted, this camera does not let me see the cylinder walls and it could certainly be a ring has given up.
No evidence of leaking head gasket, but is also why I was thinking of trying a leakdown. At least that might give me and idea of where all that pressure is going.
I'll report back after I get that done. It should hold pressure as long as the piston is above the transfer ports.
I'm beginning to think it's rings. The inspection camera is 16mm and won't fit through the smaller plug hole, see if I can find a smaller camera too.
It helps to have you guys around to bounce off ideas or make suggestions.

Thanks,
Greg

 

[Greg Boswell]

Double post, deleted

Thanks,
Greg

 

[F_R]

Pulling the intake (bypass covers) and exhaust cover will allow you to see both sides of the piston and rings, through the ports. As for the reed theory, well sort of possible if the reed broke and went through the cylinder, destroying the rings as it went through the ports. But if it were me, the head would be the first thing to come off. Or maybe the bypass cover on the affected cylinder.

The crank in that motor would be next to impossible to twist and still rotate.

I still can't relate no compression to hitting something underwater. Please let us know what you find and not leave us wondering.

 

[emdsapmgr]

Any chance that the abrupt experience was actually an engine failure event? Maybe a ring let go and it got jammed between the piston crown and head. An abrupt lockup like that could make things interesting at WOT...even damage a tee. Agree, pull the low compression head.

 

[Greg Boswell]

Ahh!, well newby mechanic here. I see the logic in pulling covers off now. Thanks. Will have to re-read that section on engine tear down, completely missed it.
See if I can get on it here today or tomorrow.

Very thankful the crank can not be twisted. Not sure how an abrupt stop could cause it to all of a sudden have low compression either. The engine still runs goodish and will hole shot well enough, but is obviously not hitting on all 4 like it should. Inspection of the piston tops indicates it is firing in that cylinder cleanly.

I'm thinking that I was running it too hard and overheated it causing ring damage and just coincidence I hit something. I just never heard the overheating buzzer/alarm and motor never lost power requiring me to throttle back like it has in the past. I did run through some seaweed once a few years ago and it caused an overheat which made the engine slow down and buzzer sounded. I just had to slow down, cleared the seaweed, let it cool down and re-started. It was back to normal in a few minutes.

It will still start up out of water and rev to the moon, but in the water it is a little fussy. Just never heard it make any expensive noises and it still runs.

I'll check and report back, get some pics too

Thanks guys..
All the best,
Greg

 

[Greg Boswell]

Any chance that the abrupt experience was actually an engine failure event? Maybe a ring let go and it got jammed between the piston crown and head. An abrupt lockup like that could make things interesting at WOT...even damage a tee. Agree, pull the low compression head.

Pretty certain, I dodged a bullet on that possibility because it is still running. We ran all weekend, well both days with me trying to sort out why it was harder to start and dying when put into gear. Still, other than it not seeming to make full power, it ran well and did not leave me stranded. Not smoking either!

The stop was so abrupt, I thought I had run aground, but we were a hundred yards or more out in the bay and I am pretty familiar with it as it is our back yard. There are no secret sand bars. Maybe a submerged tree branch, but even then something should have floated to the surface. I'm guessing it was one of the Bull Sharks or a big Gar or Catfish, something with a hard head to dent my prop.

Can't rule out that it ingested a ring, but then there is the dent on my prop that was not there prior to the event of it stopping hard.
I want to do a leak down test before I try to loosen bolts and start breaking this thing down, as I am finding the old bolt heads can break due to advanced age of the motor. I looked at the rear cover plate and those bolts have not been touched in a long time. I removed and outer cover on the back of the housing over the weekend and one of the bolt heads twisted off and I was being very careful with them all. I will just have to be very patience and careful, use lots of PB Blaster.

All the best,
Greg

 

[Greg Boswell]

Pulled the back cover plate off tonite and busted off three bolts in a row. Kept going and two more broke off. Geez!

Anyway, its the rings or at least the ring on the #2.. Barely tell, but I can feel a definite crack through one of the exhaust ports on my fingernail. Engine still turns over smoothly by hand with all the plugs out.

Could not see that the upper piston has a bad ring, but it must not be far behind due to its lower compression than before. No apparent damage to either piston.

So, the only thing I can figure is that when I came to such an abrupt stop, the wave pressure that slammed into the stern must have pushed some water up the exhaust and caused the ring to just shatter. If that is even possible. It is just so ironic that one event and I am now experiencing this.

I have spent a lot of time and money on this one. Was taking an inventory of the overall age and condition. Just replaced the water impeller and gear oil while I was replacing the Tee on the trim and tilt ram, just replaced the steering tube, steering cable and steering wheel, along with new control cables last year. Rebuilt carbs, trim and tilt rams last year. New coils, rectifier, fuel pump kit, fuel lines...

The two main bolts that hold the steering arm on the engine were never replaced. Even the dealer has told me that once they go it's all over. But he was trying to sell me a trade in on a re-power which had worse corrosion on its arm. When I asked if they can be replaced, he said not possible without much effort.

Looked at rebuild kits at around $800 to $1,000. Plus would need to rig/buy/rent a hoist to pull the power head off and eventually take it to a machine shop for overbore/cylinder honing. Or, just buy a rebuilt power head. Probably not save much at this point on just buying a rebuilt power head over the luxury of doing it myself.

Then my project manager tells me to sell/trade/donate it and buy a new boat. Going to think about this turn of events. She knows our best boating weather is coming up between now and winter and even through winter, we have many perfect boating days. I know my schedule will not let me do a proper rebuild in time..

Don't beat me up too bad, but I think I'm going with her on this and tomorrow we go look at new boats. I kind of like that little Glastron 16...

All the best,

Greg

 

[emdsapmgr]

More likely the ring failure was due to internal powerhead problems. Such as internal overheating on that one cyl-such as problems with the water diverters (deflectors) in the cooling passages around the cylinders. Or problems with fuel delivery, causing a lean condition. Possible debris in one of the main jets-could cause a lean condition and insufficient fuel to keep the cyl cool. You need to go looking for an internal failure before you do any startup of this overhauled powerhead.

 

[Greg Boswell]

Yes sir! I remember you helping me get my carbs sorted out a while back. In my excitement to get in the water, I forgot to dob some grease around the throttle shafts. They are a little worn and could stand to be re-bushed. The grease was a little cheat I did to help keep that vacuum leak from causing al lean run.

Talk about shooting yourself in the foot. The power head will have to come off and gone through. I would have to do all four cylinders, bearings, etc. and make it a solid rebuild. Of course, it will entail going through everything and making sure the diverters are in place and not clogged. Getting carbs re-bushed. Maybe find a way to replace the corroded bolts holding the steering arm on. (side note, even 4 and 5 year old motors show corrosion in this area). Went to the dealer and looked and new and some used. Came home without one in tow.

First, I'll have to find a compatible rebuild kit if one even exists or cobble the parts together and make one. Seems like they only go back to 1978 and mine is a 76 or 77. Had a better look at ones I was researching other day and I guess I just need to call and ask some questions. Pistons appear to be flat top and I can feel them touch my little finger at TDC through the spark plug hole.

 

[emdsapmgr]

Don't give up too quickly on the rebuild. The factory still makes standard .020, .030 and .040 over pistons and ringsets for 1974 and up crossflows. Powerhead gaskets: 2-318358 head gaskets plus 1-388602 powerhead gasket set.

 

[Greg Boswell]

I am not sure that I am in a position to tackle a rebuild at this time. I have hand tools, torque wrench, ring expander and compressor etc. I rebuilt my VW's back in HS and college several times and for friends, understand need for balancing the rotating parts and matching deck heights, so not intimidated by it, but not set up with a work bench or hoist or time to do it properly currently. I need to get a good work area set up so if I walk away for a week or days it is not disturbed.

Thank you for taking time to research part numbers for me. I would imagine bearings are fairly universal. At least it didn't grenade on me and I have a re-buildable block.
All the seized and busted bolts that I'm going to have to drill out and tap. Not looking forward to that task, not at all. LOL!

Cheers!

Greg