Looking for info

I'm not quite certain that this is the best forum for this question, but I didn't see a more obvious choice so here goes.<br /><br /> I'm in the process of buying a used boat with a 1978 175hp Johnson. I'm looking for info on this motor such as whether or not it's a cross flow or looper, recommended spark plugs, charging system output etc etc. A condition of me buying it is a test drive this spring once the rivers are wet again, what should I look for that would indicate a motor I want to avoid? The model number on the mounting bracket is 175TL78C. I've also got some questions about the prop that the current owner is using, but I'll post those over in the prop forum. <br /><br /> Thanks for any sage advice you gentlemen can provide.

Re: Looking for info

I believe it's crossflow, I think loopers came out in the 80's. Book says Champion QUL77V, but that may be superceded. This motor is either 6,10, or 15 amp charging. I couldn't tell you which. And you get what you pay for....check into it like you're buying it for your kid to use. Have it inspected if you can. Test drive it, but don't rely on just running it on the muffs in driveway as the way to test the motor. The best prop is the one that gets motor at right RPM's at WOT. #of blades and what it's made of are solely up to owner.

Re: Looking for info

You might want to check the compression. Also, tap the LU drain screw and see what initially comes out.

Re: Looking for info

Compression should be 100+ psi and even on all cylinders.<br /><br />With the s/plugs removed, the spark should jump a 7/16" gap with a strong blue lightning like flame... a real SNAP!<br /><br />Gearlube should be "HiVis" (available at Wal*Mart, K-Mart, any marine dealership. It should look like heavy motor oil.<br /><br />Spark plugs should be Champion QL77JC4 plugs, gapped at .040 .<br /><br />Charging system (alternator) output would be 12 amps. It is a crossflow engine.

Re: Looking for info

Yeah, black and smelly means it's been too long since last changed. Milky looking means water intrusion. Be on the lookout for metallic particles. Compression when checked shouldn't vary more than 10% in each cylinder and good numbers are typically around 100 or higher, but 90-95 is acceptable.

Re: Looking for info

Thanks folks, those are all good looking suggestions. I have the boat in my driveway for the winter so I should be able to get around to looking at this of those things this weekend. Assuming the weather is decent for being outside, unlike the last week or so. 34 degrees and drizzle/rain does not a good time make.<br /><br /> Does anyone have a recommendation for a good tach? There's currently one mounted in the dash, but it looks like it's seen better days.

Re: Looking for info

make sure compression is taken on a warmed up engine with it in full throttle

Re: Looking for info

Originally posted by andy6374:<br /> make sure compression is taken on a warmed up engine with it in full throttle

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I'm glad you mentioned that as I wouldn't have thought to do that. Come to think of it, I have no idea how to actually do a compression test. Engine running or just cranking with the starter? If running, is that safe to do with muffs or should it be in a test tank?

Re: Looking for info

Get the engine running and warm. Kill the engine. Then remove all the spark plugs. Then pull the kill switch (no spark). Now individually measure the compression in each cylinder.

Re: Looking for info

muffs are fine.

Re: Looking for info

Originally posted by andy6374:<br /> Get the engine running and warm. Kill the engine. Then remove all the spark plugs. Then pull the kill switch (no spark). Now individually measure the compression in each cylinder.

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Kill switch? I'm assuming you mean something other than the ignition switch since that would be on as part of cranking the motor with the starter.

Re: Looking for info

I know I'm digging up an old thread here, but I wanted to wrap it up. As it turns out there was some drama with this motor and I ended up not buying the boat. I had a mechanic take a quick look over the motor to see why I couldn't get it to start. He discovered that the middle cylinder on the right hand side (from the back) was only reaching about 30psi. A quick look through the spark plug hole showed some pitting on the piston head.<br /> I subsequently arranged for the seller to pulls the head off for me and it wasa bit ugly in there. Not only the middle cylinder but the one above it as well showed significant pitting and gouging of the piston and cylinder heads. There was also parallel scoring of the cylinder walls. I could say for sure, but I'm inclinded to think a piston ring let go and broke up. The pistons seemed to have a little more wiggle to them than seemed proper. From what the seller said, he was unaware of this situation and had possibly run the motor like this for a year or more. I never was able to get it started either.<br /><br /> Now I have a new (to me) boat and some fresh questions for a new thread