'73 6HP Johnson blown head gasket? how to replace?

[orcahead]

I bought a 73 Johnson Seahorse 2 cycle 6R-73S, serial J3729766 late last year - my first outboard. It won't start except for an occasional bang and I think the head gasket is blown and I need info on how to change it and how much skills I need. <br /><br />First, here's the diagnosis: Everything was working fine last year for the hour I used it, and I winterized it. I started the engine up fine this year and ran it in a bucket & running water. Everything was fine w/o load. I put in new fuel mixed well w/ 50:1 Briggs & Stratton 2-cycle oil (West Marine guy said that was fine), and put it in the water. At forward idle it was fine, then when I put it up on plane it suddenly cut way back - below idle speed. I put it into neutral and the engine revved fine. I did this about three times with the same results. Gas was almost at engine height with a brand new hose. Finally it died. When I try to start it now it doesn't do anything for many pulls and then goes bang! It has good spark on both plugs, new fuel mixed w/Valvoline marine 50:1, fuel squirts good into the carb, fuel from bowl looks good. Compression on both cylinders, however, is very low at 45 PSI. I verified the tester on my leaf blower (120 PSI). From a conversation with a shop it sounds like I may need my head gasket replaced. The old owner says it's never been replaced. He doesn't think I overheated it - he says the cylinder would have frozen. <br /><br />I have a Clymer manual which is very vague but I did find a picture of the head gasket & cover along with torque info (60-84 in-lbs) and tightening order. What I'd like to know is the folowing:<br /><br />1) Where do I get a head gasket? Can I get it from any firm dealing in outboards? Is this just a cork gasket - do I need anything special?<br />2) What skill level is needed to change one? I'm mechanically inclined and done auto maintenance, but never opened an engine before. The local shop wants $110/hr so I'm willing to learn <br />3) Can I replace the gasket without dissassembling the engine? The cylinder head is at the back of the engine and has the spark plug holes, right? There's plenty of clearance to remove the bolts without dissassembly. The bottom two bolts don't have clearance for a torque wrench for installation. I'm thinking I can just watch how much I torque the other bolts and do the same?<br />4) Anything need to be done to the gasket & surfaces besides scraping off the old one and applying a little oil? I see lots of info on gaskets inside the engine but the head gasket is glossed over.<br />5) Assuming this is the problem, what caused my blown head gasket? I read that overheating can cause it although I can't figure out how I did that except maybe I didn't run enough water in the 5gal bucket. I felt the water coming out of the engine and it was warm, but not scalding hot. Do these things fail of natural causes?<br />6) My spark plug wires look crossed but I'm not sure the wire mounting is supposed to correspond to the cylinders. How do you determine which wire goes to which cylinder?<br /><br />Many thanks in advance.

 

[REELSPORT]

Re: '73 6HP Johnson blown head gasket? how to replace?

If you have a manual and a little mechanical skills you should have no problem replacing head gasket. Motor does not have to be broke down to replace. you are correct the head is where the spark plugs go take your time and report back your results. By the way welcome to Iboats and good luck

 

[Xcusme]

Re: '73 6HP Johnson blown head gasket? how to replace?

Orcahead, Welcome to iboats! <br /><br />Replacing the head gasket is not a big job. Any OMC dealer should have one for ya. If you have a Nappa Auto Parts store out your way, they should have the gasket too. Some gaskets don't need any extra sealer, they are usually labeled. Getting the mating surfaces flat is a must, especially if you did have an overheat condition. Dress the head with emery paper on a flat surface(plate glass is good), using a figure 8 motion. With the head removed, inspect the cylinder bores for any heavy scoring. Clean the tops of the pistons of any carbon deposits. Clean out the cooling passages if needed too. Install the head and gasket. Install - tighten the bolts in a circular pattern starting in the center, working in a clockwise direction. Torque the head bolts in a series , first at 1/2 torque, then again at final torque. <br /><br />The backfiring could be caused from sheared flywheel key. Find a harmonic balancer type puller, it will have (3) 1/4-20 bolts to install. Pull the flywheel and inspect the key in the crankshaft taper. The flywheel key indexes the flywheel to the crankshaft and determines the timing of the motor. The flywheel key can shear from a backfire or from not being torqued to specs.. BTW, The front most coil is for the #1 (top) cyl. Check the point gap (should be .020) . Rotate the crankshaft until the crank key points to the rub block on the points (this is the high side of the cam) and check the point gap for .020. Inspect the coils, if either is cracked, replace them both. When you re-install the flywheel, don't use any oil on the crankshaft taper, it's a dry fit. Torque the nut to specfication in the service manual. Remember, Inch pounds are different from Foot pounds!<br /><br />Find a bigger bucket! A 5 gal. bucket is a bit small. You have to cover the lower unit and intake screen with water.<br /><br />Good luck and report back with your findings.

 

[BF]

Re: '73 6HP Johnson blown head gasket? how to replace?

Hiya & welcome!<br /><br />On my '75 6hp, the way the wires run through that strain relief loop do correspond with their position (top to top)... Of course yours might be different. Aside from looking after you pull the flywheel, you could use a timing light if you've got one... The fly wheel has 2 marks that are labelled T & B (top, bottom) and are 180 degrees apart (least that's how mine is). Connect to a wire, and pull it over, the mark that gets lit is where that wire should be going. If mark isn't aligned between the 2 lines on the timer base, than you've got big timing problem (like sheared key already mentioned).<br /><br />Hopefully when you pull the head off, the cylinders look OK... You might wanna pull it off before you go running around for a new gasket, just in case it has bigger problems (broken rings/scored cylinders).<br /><br />Good luck!<br /><br />Brent

 

[CF-DRG]

Re: '73 6HP Johnson blown head gasket? how to replace?

Xcusme knows what he is talking about.... Head gasket is probably one of the easiest gaskets to replace ( on a 2-stroke )... to answer your # questions...<br /> #1 you have to get a "head gasket" (it is not cork) from dealer or NAPA... you'll see it has 2 metal rings on it that seal off the cylinder and head from the water jacket..<br /> #2 Skill level....... we'll you have it.. <br /> #3 Yes... all I can add to this is when tighting the head bolt I go in a criss-cross pattern.. so if it were a clock face start with 12 and snug it, then 6 snug it, and then 1 and 7 2,8,3,9 ect till there all done, than start to torque in that same pattern building up the torque too the specified amount(usually about 3 cycles of the pattern)..as far as torquing those two bottom one's, you can go by feel...just remember they are SS bolts into Alum...<br /> #4 Both surfaces have to be "clean"... as Xcusme said go with the "glass and emery paper"<br /> #5 Your head gasket could of blown because of age...Its a hard call, but sometimes they just go..<br /> #6 has been answered<br /><br />You didn't mention if this was a fresh or salt water engine, just that salt build up in the Head water passages can cause a gasket failure...

 

[Paul Moir]

Re: '73 6HP Johnson blown head gasket? how to replace?

The think about #6 is if the spark plug wires are crossed then the engine won't run and all you'll get is the occasional BANG.<br /><br />It cannot be a sheared flywheel key because on points systems that'll cause spark to be lost not bad timing. That's only for later outboards that use magnetic and optical pickups. Otherwise, Xcusme has givin you great info on tending the ignition system.

 

[Xcusme]

Re: '73 6HP Johnson blown head gasket? how to replace?

Nice catch Paul! I just gotta resist responding in the wee hours of the morning. Keeping point systems and CDI's seperate can be challenging at that hour.<br />Thanks again.

 

[orcahead]

Re: '73 6HP Johnson blown head gasket? how to replace?

Thanks to everyone for your information. Good news - I pulled the head off and found the head gasket had blown between the cylinders. It was original and did not have the metal rings around the cylinders. The cylinder walls are pristine.<br /><br />I found a local outboard shop who can order me a new one. I also found that my spark plug wiring was correct although the wires were mounted crisscrossed. A few more questions:<br /><br />4) Follow-up to gasket prep: I get the concept of glass and emery, but I don't have those. Do I need a rubbing surface larger than the entire head? Is emery paper the same as sandpaper - what grit? <br />7) Cleaning passages: The inside of the cylinder head is caked black. More concerning is that the passages outside the cylinder are caked with a white waxy deposit. This is a saltwater engine. Part of this is because the engine died in saltwater and I couldn't flush it, but some of this has been building a long time. A few of the passages look to have been completely blocked. What's the best way to clean these?<br />9) Thermostat: The clymer manual shows a thermostat plug screwed into the cover but mine has a triangular extension w/cover on top. One of its passages was pretty much blocked off by both salt and some big pieces of rust. I'm not sure which way is open or closed, but I tested it in 160F water and it didn't do anything, so I assume I need it replaced as well.

 

[orcahead]

Re: '73 6HP Johnson blown head gasket? how to replace?

Success at last! Once I had the right tools, lubricants, and parts it wasn't hard, but it did get much more complicated than I had originally hoped. (Hint: Get a 20-200 in-lbs torque wrench at HarborFreight.com item 2696 for $30, get a small can of OMC Gasket Sealing Compound for about $4 at your local marina.) I changed the head gasket and thermostat and boosted the compression to around 90 PSI in both cylinders. <br /><br />It still didn't start and kept going bang. The local shop guy said it must be my flywheel key but thanks to the posts here I realized it must be the spark plug wires. Sure enough, my spark plug wires must have gotten crossed at some point after it died. It started up on the next pull! However, I was getting no water out the exhaust port half way up the shaft. I opened the head gasket to inspect the inner passages and they were dry!<br /><br />I decided to go for the impeller replacement. I was a bit intimidated by the instructions, but it also wasn't that hard. (Hint: it's not necessary to remove the prop or drain the gear lube to change the water pump) The old impeller actually looked ok, but there was tons of crusted salt and calcium that I cleaned away. I did notice the impeller was loose around the shaft connection so it may not have been spinning.<br /><br />A head gasket, thermostat, switched spark plug wires, and a water pump kit later it started up and was spitting water out the back! Thanks very much for all your help and I hope someone else gets some benefit from this posting.

 

[byronjacobson]

Re: '73 6HP Johnson blown head gasket? how to replace?

hi,
i've been reading messages and have been learning a lot. can someone tell me how to start a new threat on iboats?

i am registered but have no idea how to start a new thread.

please send your answer to my email at jake331@charter.net

thanks.

 

[byronjacobson]

Re: '73 6HP Johnson blown head gasket? how to replace?

I finally figured out how to post questions. tomorrow i'm doing the head gasket on my 6 hp evinrude.
what is the answer to the emery versus sandpaper. are they the same, if not what grit is emery. how long does a person do this figure 8 pattern with the head.
also i have a torque tool in foot pounds. will that work just as well as one in inch pounds provided i divide the footpounds by 12, for example 60 inch pounds would be 5 foot pounds.