15 hp - no compression on one side

[jbjennings]

Re: 15 hp - no compression on one side

Had my son-in-law over today for Easter dinner. He is a farmer and a ticketed diesel mechanic and a boater to boot. He looked at the head, and has a good theory as to the cause of the break. He suggests the motor was not drained properly and then stored with the head down. There was likely a pocket of water formed at the bottom of the head and then froze, breaking out the water jacket at that point. That would explain why the broken area was very clean with no carbon marks. Could be right. Anyway, will try to get a replacement head and report back. Thanks again.

I think it is a good hypothesis:

This would explain why the guy said the motor was good and it ran well before he set it up (or down????).

The chip could have been in the cylinder and after all the attempts at cranking, might have passed out the exhaust port.

I have found that it's rare for a person of reasonable intelligence not to spot a liar right away, or in most cases, steer clear of them altogether based on careful observation of the liar's surroundings. I'll bet the guy was truthful. The weirdo head problem with no cylinder scuffing seems to point to this.

Later,
JBJ

 

[bison716]

Re: 15 hp - no compression on one side

Picked up a used head today along with a new head gasket. It now has compression on both cylinders, the dead cylinder has a good pop against your thumb and the recoil has an even pull. Will have to borrow a compression tester for a reading. I will try to fire it up tomorrow. Fingers crossed.

 

[1946Zephyr]

Re: 15 hp - no compression on one side

Well, there's a good sign. You didn't get hurt too badly on this motor then.

 

[bison716]

Re: 15 hp - no compression on one side

Fired her up this afternoon, 2nd pull. Seems to run nice but I still need to do a compression test. However, there was no water coming out the outlet, even after a minute of fast idle, then I shut it down. Shouldn't there still be a stream with the ear muffs on? Guess now it's time to pull the bottom end apart. Progress at least.

 

[bktheking]

Re: 15 hp - no compression on one side

You asking about the telltale stream? Probably plugged up as they all seem to plug up over time, try cleaning it out before pulling it apart.

 

[1946Zephyr]

Re: 15 hp - no compression on one side

And if you can't get any water out of there even after trying, then remove the thermostat housing and see if it is pumping water really good to that point.

 

[bktheking]

Re: 15 hp - no compression on one side

Easy on these later motors to pull the stat, they finally got it right with that setup.

 

[bison716]

Re: 15 hp - no compression on one side

I dropped the lower unit tonight and it was very evident why I wasn't seeing the telltale stream when I had it running. The rubber boot connecting the water pump to the tube was pushed off to one side and was totally out of place. No wonder I wasn't getting water up to the engine. I will install a water pump kit while I have it apart. However, another issue came up. When I started to drop the lower unit, I found there was only 5 bolts instead of 6. Now I can look at the bottom of the housing, one bolt hole is filled in with silicone and you can see the hole is oblong so it is likely totally stripped out. Another bolt hole is broken out as you can see in the attached picture, but the bolt still threads in OK. What to do? Should I JB Weld the broken out hole and only run with 5 bolts? Is that enough? Looks like a ton of work to remove the lower housing and likely not a cheap part to buy. Any suggestions would be much appreciated. Thanks.

 

[bktheking]

Re: 15 hp - no compression on one side

Leave it, it won't hurt anything with one less bolt. Glad you found out the issue.

 

[bison716]

Re: 15 hp - no compression on one side

Borrowed the same compression tester again tonight. Readings were 90 on the previously dead bottom cylinder and 92 on the top cylinder. Likely on the low side, but even at least. I will run it like this for now and possibly re-ring for next season. I may try to use a different tester just to get a comparative reading in case this tester just reads on the low side. Waiting for my water pump kit now and hopefully the project is near over. Going to re-paint the hood with new decals. Thanks again all for the sage advise and quick responses.

 

[1946Zephyr]

Re: 15 hp - no compression on one side

Well, if the cylinders are within 10% of each other, you're okay. Your's are within 2 psi of each other and that's really good. I think once you run that engine for a while and get plenty of fuel mix worked in around those rings, things will improve. You could do a decarb on the motor, once you get it running good. Myself, with all the motors I've worked on, never did a decarb, but plenty of guys here would recemend it. I guess this stuff cleans out all the carbon build up from around the rings and stuff and gets it freed up good.

 

[bison716]

Re: 15 hp - no compression on one side

Got the water pump kit in and fired her up today, I get a good telltale stream now but there is water coming out at the front edge of the bottom end split. I had it running on the earmuffs so I'm thinking it's due to the water pressure. Block is warm but not hot, so I think all is well. Seems to run and idle very nice, have to wait a month or so for a lake test. Hood is out getting painted and new decals on the way. I think I'm out of the woods guys, so thanks very much again for all the good pointers and advise. Have a great summer.

 

[CATransplant]

Re: 15 hp - no compression on one side

pull start motors give the same comp reading as elect start motors, if not then you would have a very bad leak down problem it sounds to me like you have a bad comp gauge, all 2 cycle motors need a min of 88psi to make a fire stroke really im not making that up its the truth

Not so, on either count. If what you say were true, there are a whole bunch of old 2-stroke inboard motors that would never have run. Compression was very low on those, and they ran for years and are still running, at least some of them.

Also, it's hard on a pull-start to get the same compression readings as on an electric start.

I had a 1958 Johnson 35hp that never had more than 80 psi of compression. It ran like a top.

 

[CATransplant]

Re: 15 hp - no compression on one side

hahaha ok tell me why a pull start motor is going to have less comp then an elect start motor, ive been a cert omc mecanic for over 20yrs and been working on motors for 35yrs and they never told me in omc 1, omc 2, omc fuel inj school, or on my omc master classes that a pull start motor has less compression then an elect start motor, when you do a comp test on a motor every time you pull the rope the comp is gonna climp till it hits its max unless you have a 20 dollar harbor freight comp gauge that wont hold pressure, the only way you would get a diff reading is if you are checking a motor like a lawn mower that has a comp releese so its easyer for you to pull, no omc pull start motors have this on them. hahaha some of you guys crack me up no wonder we ended up with oboma for our pres

This is not a political forum. Save that for some other forum. And, besides, it's spelled Obama.

 

[torbjorn]

Re: 15 hp - no compression on one side

My nearest dealer is 80 miles away and they don't have a head in stock. One of my coffee buds reminded me there is a pretty good machine shop in this area not too far away and maybe they can weld it and mill it straight. Will talk to them next week. It's worth a try. As far as the other questions, I checked the cylinder walls again today and there is not a mark on either one. Smooth as glass. I'll see what I can find out this next week and keep you posted. Thanks.

Smooth as glass means worn rings, bad seal. You need to see a cross hatch pattern.

 

[bison716]

Re: 15 hp - no compression on one side

By smooth as glass, I meant there were no grooves worn in the cylinders. I could clearly see a cross hatch on the walls. It might need rings, but will lake test it first. It sure runs nice on the test stand.

 

[bktheking]

Re: 15 hp - no compression on one side

Did you end up buying the ebay head, I noticed it sold.

 

[bison716]

Re: 15 hp - no compression on one side

No I didn't buy that one. Found a used head at a Johnson dealer for the roughly the same price and much closer.

 

[bktheking]

Re: 15 hp - no compression on one side

Cool, now that's it's running check the head temp if you can with a laser thermo, make sure nothing happening temp wise.

 

[bison716]

Re: 15 hp - no compression on one side

Don't have a laser thermo, but I did do the "hands on" test. It was warm to the touch but not anywhere near hot. Just to be on the safe side, I have ordered all the thermostat parts and will replace them. The rubber bellows are on back order, hopefully not for long.