Does this head look burnt?

[mostlysnow]

I have a '72 25 hp evinrude I just recently replaced the impeller (water pump) it went out in '07.
after putting back together I was able to run the engine in a barrel of water (mostly at idle) water was circulating good and it would start on the first pull I was real proud to accomplish this, so I decided to hook truck up to trailer take to the lake. I ran the engine there a little before even unloading it (while in the water) to make sure it still woud start yeah it started on first couple cranks with electric starter and water was still circulating so I decided to go ahead unload and take it to the peer, and put the truck up while I was doing so I left motor running (kind of to warm it up) got in the boat to do a little floating around just puting along, got it up to about 5mph then up to 9mph we got about 1/4 mile from the peer and she started to sound different, no screeching or anything just sounded like a bogging down motor. then she finally died and I could not get her started again.
Loaded her back on trailer brought her home noticed it looked as if it got hot...I have spark, I have fuel (fresh 50:1 mixture) just filled up before going out. The tank vent fully open... anyhow I can not get it to even cough so I did a compression check got about 50psi top and bottom 60psi. I am guessing this is not great but good enough to at least run.
I am ashamed I didn't change the thermostat but I am thinking this might have caused the overheating, but now it is said and done need help deciding if head looks shot or not, any ideas will be appreciated, Thanks in advance

 

[F_R]

Re: Does this head look burnt?

Yes, that baby's been hot. And 50-60psi compression is way too low. If you are lucky, it blew the head gasket. If not so lucky, you burned up the pistons.

Whatever, at a minimum, you need to replace the head gasket and exhaust cover gaskets. While you have the exhaust covers off, you will be able to see if the pistons are scored.

Don't be deluded into thinking you can get away without doing the exhaust. It is sure to leak, and may blow water into the cylinders.

Oh, and fix the cooling problem.

 

[crxess]

Re: Does this head look burnt?

Wow that head really got hot.
1/4 mile isn't very far. Once you pull the head, do a really close inspection of all the water passages. Looks like No water around lower part of the head/block at some point while running.

 

[1946Zephyr]

Re: Does this head look burnt?

That looks like a major OUCH. I've seen powerheads that had all the water passages completely plugged with corrosion, because they weren't flushed properly after salt water use. Small passages, such as where the thermostat is, are easily corroded up and the thermostat seizes up. I have ten bucks that says your pistons are shot. You'll most likely have to do a complete tear down and put new pistons and rings in it. Earlier this year, I had a 15 hp that overheated almost to this extent and each piston was scored in at least three places. Luckily, mine still ran good, but I know the compression was not as good as it should have been.
Well, I wish the best for you. I hope things turn out okay.

 

[mostlysnow]

Re: Does this head look burnt?

Hey thanks for the input, wouldn't there be some bleed down in my readings if the pistons were shot? Or even if the gasket had a leak? also when the water is going thru the head is it after the thermostat or before, (top to bottom or the other way around) I am just curious the direction of flow

 

[crxess]

Re: Does this head look burnt?

With that kind of discoloration you want to visually confirm any damage or lack thereof. New gaskets are cheap insurance and you will know exactly how everything is inside.

Water pumps through the pickup tube to the block. Across to the head/Thermostat. While the thermostat is closed,water bypasses through small passages above to allow circulation. Once the T-stat opens secondary passages carry increased water flow.

Definitely replace the T-stat while you have it down.
Check the head to make sure it isn't warped. Sand it to true if needed.

All this can be done in an afternoon with parts in hand.

 

[F_R]

Re: Does this head look burnt?

Hey thanks for the input, wouldn't there be some bleed down in my readings if the pistons were shot? Or even if the gasket had a leak? also when the water is going thru the head is it after the thermostat or before, (top to bottom or the other way around) I am just curious the direction of flow

"Bleed down"? Not without a leak-down tester. A compression tester has a check valve in it that will hold the pressure all day. Besides, compression is only part of the story and mostly is a result of rings and cylinder wall. What most people don't realize is that on a two-stroke, the piston skirt acts like a valve. If the skirt is all scored up, air is bypassed from the exhaust area, back into the crankcase (intake area). It won't run worth a hoot if that is happening. That is one reason I said to remove the exhaust covers and look, and replace the burnt gaskets.

Water flows through the powerhead thru two routes. One route is always open and the other one opens with the thermostat. BOTH routes flow through the cylinder head, so the thermostat was not the problem.

 

[mostlysnow]

Re: Does this head look burnt?

"Bleed down"? Not without a leak-down tester. A compression tester has a check valve in it that will hold the pressure all day. Besides, compression is only part of the story and mostly is a result of rings and cylinder wall. What most people don't realize is that on a two-stroke, the piston skirt acts like a valve. If the skirt is all scored up, air is bypassed from the exhaust area, back into the crankcase (intake area). It won't run worth a hoot if that is happening. That is one reason I said to remove the exhaust covers and look, and replace the burnt gaskets.

Water flows through the powerhead thru two routes. One route is always open and the other one opens with the thermostat. BOTH routes flow through the cylinder head, so the thermostat was not the problem.

After reading this it dawned on me about the check valve I was not thinking I guess thanks for pointing that out.

As for your diagram I like it and it sums a few things up thanks while looking at the diagram I am seeing a water outlet midway of shaft housing is it ok to run motor with this outlet below the water line? I am talking about three to five inches give or take below water level. Depending on the waves behind me.

Update ...I took thermostat out and while motor in barrel of water turned motor over no water came out of the thermostat bowl (don?t know what to call it) I was checking to see if impeller was still good? I put hand over and felt what I thought was puffs (pressure/ outflow) my brother put his hand over it and he felt vacuum (suction/ inflow) what is it supposed to be felt here?
We then poured water into the said bowl and it came out at the upper outlet hole midway the shaft housing don?t know if it came out the bottom outlet since it is still in the tank of water?I am guessing ports/water jackets are ok so far right?

After investigating this I went ahead took the head off since I have one ordered might as well get it apart to clean right? The head bolts were loose just barely had to use wrench except for two or three of them? possible compression problem (I hope keep fingers crossed)
Anyhow I was shocked to find piston tops were, in my opinion, not in bad shape and the cylinder walls still have signs of the hash marks made from when it was last either bored or honed, and no ring ridge at all? anyhow I took pictures but they didn?t turn out but you can see the pistons which I have posted pictures of them. I inspected the head just briefly and it looks clean (probably burnt what was on them when it got hot) anyhow no noticeable cracks (thank god) I looked at the gasket and didn?t find anything here neither (was looking for some sort of blow-by.)

As for the exhaust cover you mentioned is it on the side has about eight or ten bolts? Maybe twelve anyhow I will show you a picture?By the way I have a book ordered too just FYI should have bought one long time ago.

 

[F_R]

Re: Does this head look burnt?

mostlysnow, the following is a copy of the answer I sent you in reply to your PM:

Your pictures do seem to show some blackness on the gasket sealing area at about the 5 o-clock position, upper one being worse than the lower one. That, combined with the lower compression reading on the upper one and the loose bolts are all consistant with leakage due to overheating.

You are heading down the right path. Clean all that stuff up and install a new gasket. The cooling passages look pretty good. Don't attempt to remove the red sealant in them. But do look closely for any chunks of rubber from an old shattered impeller.

But you are not done yet. You still need to replace the gaskets on the exhaust cover--yes the thing that you took a picture of. If I am seeing it correctly, there is a bit of melted vinyl from the spark plug wires stuck from it. That thing has been hot to melt that vinyl. But not so hot as to burn the paint---a good sign. But it was hot enough to damage the gaskets.

And, I won't rest easy till you report that the piston skirts aren't scored. You have an engine that won't run and there is a reason it won't run. You need to find out why it won't run.

I don't think you can get that exhaust cover off without removing the powerhead, can you? So, the powerhead question becomes a moot point. When you do remove it again, use a new gasket.

Again, be on the lookout for any chunks of rubber.

Even with all this, unless you have found rubber chunks, you still haven't found the cause. You can test the thermostat in hot water. It should be open at 160 degrees.

If you still haven't found the cause, it is on to the water pump. Something is wrong someplace. It didn't "just happen".

Sorry, but there are no short cuts. A lot of work, yes. Hey, I never said it would be easy. But you will survive. I survived doing it every day for 24 years.

 

[mostlysnow]

Re: Does this head look burnt?

Daily update for those interested...I took engine back off boat placed on saw horses and took lower unit back apart...before seperating the units I looked inside the side cover where you have acsess to shift linkage, and found the copper tubing that goes from water pump to top of exaust housing was not in proper place so either I didn't have it in it's place properly or it came out (is this possible can they fall back out after engine is back together??)

anyhow I took the water pump back apart to make sure couple things...
1. to make sure impeller was not burnt up
2. to make sure impeller was facing right direction (see picture)
3. to make sure didn't suck anything unwanted
4. to make sure the "key way " for impeller was not warn out. or missing.

I inspected everything found all to be in working order, so now I am waiting on Head gasket and will keep you up to date.

I am including a picure of the cylinder wall I finally got a picture to turn out.

 

[F_R]

Re: Does this head look burnt?

or it came out (is this possible can they fall back out after engine is back together??) [/U][/B]

.

Ain't no way it can get out after being properly installed. Insert it into the upper grommet first, then you can see what you are doing as you install the lower unit and align the tube into the lower grommet.

 

[Rick.]

Re: Does this head look burnt?

While you have the head off you should resurface it. Get some 120 grit sand paper and a piece of glass. Lay the paper on the glass and keep moving the head over it in a circular motion until your getting signs that it is nice and true. This is important IMO. Rick.

 

[mostlysnow]

Re: Does this head look burnt?

Well here is a UPDATE for those who are following this thread...I got the side cover off tonight, and took a look inside and found only minor damage just a few scratches nothing to be felt. I do think I got very lucky!!!

FR if you read this can you look at the side cover that I have circled does it look as if it might have leaked one time or another? And is that why you can see the metal along that side better than the other? like the water was washing that side down. If anyone else has an opinion feel free to post them.

I went ahead and sanded down the head using 100 grit on a flat surface going in circles (I didn't have any glass or any 120 as suggested in earlier post)

Now all I have to do is wait for my gaskets for the side cover and then I am ready to put back together, all the passages/ports are clear enough I can see light through them... I would stick my LED pen at one end and look at the other and can see fairly well.

Now is there any last minute things I should look at before putting this back together?

I have new thermostat, head gasket,clean head, water pump still like new and side cover will be cleaned and new gaskets installed if you think of anything else I would appreciate your input, thanks for everyone's help I really do appreciate it.

 

[F_R]

Re: Does this head look burnt?

Yeah, you got lucky. The scratches you see on the pistons are from overheating. I have seen much worse.

Your exhaust cover gasket was leaking. It is hard to say if that is what caused the carbonless area on the plate. Maybe. Water + combustion heat equals steam--as in steam cleaning. The real danger of leaking gaskets is that the water can squirt into the exhaust ports, where it finds it's way into the crankcase and ruins all the steel roller bearings. Fortunatly you haven't gotten to that point yet. I'm glad you checked. Most people just ignore this old fool.

You did a nice job on the head.

 

[jay_merrill]

Re: Does this head look burnt?

Water flows through the powerhead thru two routes. One route is always open and the other one opens with the thermostat. BOTH routes flow through the cylinder head, so the thermostat was not the problem.

F_R, double check me on something .... I believe water does flow through the head when the t-stat is closed, but at a reduced volume as compared to when it is open.

If you look at the photos of his head (both inside and out) you can see the path of the water pretty well. When the t-stat is closed, the water goes through the top of the t-stat housing into the tube that runs down the back of the head. This tube is externally visible (see first set of photos) and runs from top to bottom. From there, it exits the motor at the midpoint of the exhaust housing.

If you look at the inside of the head (see post #13, 4th photo), you will notice two things. First that there is a square opening where the water exits the tube at the bottom of the head, which is not connected to the rest of the water passages. Second, that there is a short channel at the top of the head (to the right in the photo), with a "choked down" orifice at the end of it. This passage comes from the t-stat housing at a point above the t-stat, when in the closed position. It is through this small orifice, that the water circulates through the entire system, when the t-stat is closed.

What all of this means, is that you get a greatly reduced water flow through the circular passages in the head, as well as through the rest of the block, when the t-stat is closed. There is flow because of the metered orifice, but it is not the same volume as when the t-stat is open.

In this case, the obvious problem is the fact that the copper water tube wasn't in its proper place, but I wouldn't be surprised if you can overheat a head, due to a bad t-stat. I wouldn't think that this would happen at idle, but who knows? I don't "wrench" on enough of them to know this for sure, but it strikes me as a possibility.

Would that be consistent with your experience in takng them apart after heating problems?

This design, BTW, is shared on other OMC motors. The heads on my 6hp Johnsons work exactly the same way. In fact, other than the size difference, they look nearly identical to the head in these photos.

 

[mostlysnow]

Re: Does this head look burnt?

Hey I forgot to ask in my last post (number 13) I still have some grit from the sand paper on the head any suggestions what to use to clean that out with?, I don't want to use anything harsh I don't want to take any more paint off then already is... I was thinking of plain soapy water but was thinking I would be taking a chance on it rusting...before it was put back into service.

I was wondering what to use on the exhaust covers too?, the inner one has lots of carbon build-up, I dont think I would want to use wire brush. But I am going to need help getting old gasket and residue off. I don't have a parts cleaner, or steam service in the area that I know of. I was thinking of a machine shop might but they probably want arm and leg to do what I have.

And when I do put it back together can I repaint the head and outer cover with some engine paint without effecting heat transfer? I know there is already paint on it but was thinking this may have been put on by manufacture.

F R you said "I'm glad you checked. Most people just ignore this old fool."
I will be honest with you I didn't want to tear the engine down any farther than I had to but like CRXSS said here in this thread "New gaskets are cheap insurance and you will know exactly how everything is inside."
I am glad I did look from the looks of everything I would probably would be in deeper next time around.
I want to learn as much as I can about this because engines are not cheap and no one around here will work on anything older the 1980 not only that I don't think you would steer me wrong you have help me and I am sure many others and I for one really do appreciate what you do in this forum. I mean if I was to sit and talk with my parts man like I have in this forum they probably would not take as much time explaining things like you have to me. Thanks!!!

Lastly so do you think it would be safe to put back together now? Is there any last minute things I should check?

 

[F_R]

Re: Does this head look burnt?

Jay Merrill, your assessment is correct--sort of. But you aren't seeing the whole picture. Besides, you are testing my memory, since I don't have one here in front of me. But here goes:

If you look at the head, you will see a large round hole afout 7:00 o-clock from the end of the restricted passage. Unless I'm nuts, that comes out above the closed thermostat. In other words, water going through that hole bypasses the 'stat.

So, you may ask, where does that hole come from?

As I said, there are two flow routes through the powerhead. The first one is through the exhaust covers, through that hole we've been discussing, and bypasses the thermostat, then continues down through the vertical tube in the head. That means, there is always a healthy flow through the exhaust cover and part of the head.

The other route is around the cylinders and the area around the edge of the head. As you have figured out, that also always has some flow through the restrictor, and also has a heavy flow when the 'stat opens. The thermostat mostly controls this flow and the temperature of the cylinders.

So, two flows, one cools the exhaust and part of the head, whether the 'stat is open or not, and the other cools not only that portion, but also the cylinders.

 

[iwombat]

Re: Does this head look burnt?

Snow - soapy water will work fine. That head is aluminum, if you can get it to rust I'll be impressed.

 

[mostlysnow]

Re: Does this head look burnt?

Snow - soapy water will work fine. That head is aluminum, if you can get it to rust I'll be impressed.

I had a brain fart sorry should have known ...thanks though, it cleaned up nice I even used soap and water for the covers too they cleaned up good. Gaskets practically came right off after soaking them a while. So did the carbon build-up. Just had to use a little more elbow grease.

Just tinkering tonight I put the thermostat in the head, along with the rubber grommet thingy, whatever goes on top (it does go on top right or does it go below the stat?) the diagram on the parts page shows on top (look at the attachment part number 20 is what I am talking about), and then the gasket then I tried to put the stat cover on and the dang Grommet is too tall, any ideas? I even tried to put grommet in and then the thermostat then cover and got the same results.
The part number they ordered was 310058 the dimensions are 1" x 1" x 0.27" the one I took out was flattened to about the thickness of about 20 pieces of paper so I could not tell exactly what it looked like before it was used. I do know the material the ?original? was made of seemed thinner more flexible, You might be able to see by looking at the picture. I am thinking about putting the old grommet back in there would that hurt anything you think?

 

[F_R]

Re: Does this head look burnt?

Well, there's a new one on me. I've never seen one like the one in the left in your second picture. The one on the right is a mangled version of what I know about. Notice the groove on the inside of it--the thermostat flange goes in the groove. There is a "skirt" on one side of the seal--the skirt goes downward.
OEM # 310058
Sierra # 18-0182
Mallory # 9-60002
http://www.iboats.com/mall/image/index.cgi?view_id=364554