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not sure what direction to take

S

ship wreck

Contributing Member
I pulled the 140 I've been fighting with for the past two seasons and tore it apart today. I was advised that the compression was a bit low and it was getting lower so I figured I needed to open it up. My hope was to do a refresh but I found it ingested something and needs a new piston and cylinder bored. The head I believe will clean up but if not that adds to the cost. Everything else in the motor checks. Crank measures spot on. Other cylinders are in spec no issues other than needing rings.

So choices are:
A rebuilt power head that runs 1500 to 2500 depending on the source and maybe a bit more if there is a core issue.
A rebuild kit which is around 900 plus machine work and a marine machine shop is not easy to find here.
Or purchase a boat locally for 1000 that has a 135 starflight.

This last option has all the pitfalls that got me to where I am with this Johnson as I bought it with a boat as well but I only compression tested it never ran it in the water My thought is if I can lake test the local boat that should tell me I have a good motor but you never know what might happen down the road.

Suggestions?
 
Most likely ring broke and if it has never been into ALL the pistons need replaced as they are the high ring style. You will need to take block to machine shop and have cylinders measured and bored before you order parts. Here is link to complete kit as I don't like Siezco pistons,as need extra clearance,extended break-in as pistons have to temper and need to be near operating temp before WOT.
http://www.ebay.com/itm/Johnson-Evi...Crossflow-Powerhead-Rebuild-Kit-/381056359024
 
motor check out other than the bad hole. I have .001 out of round in the other cylinders but if I'm going to bore one then I'll bore 4. Having a hard time finding a shop in AZ. Will have to do some calling around on Monday.

Anyone have a factory service manual for a 78 Johnson 140? My clymer lists the crankpin at 1.1823-1.1828 for a '73-'78 and 1.3757-1.3762 for a '79 to '84. Mine is a '78 but the crankpin is the "'79" size. Looking at parts lists I see the same bearings and rods for a 78 and 79 so I assume it is a misprint but other listings for rebuild kits have a break point after 78. Not sure what parts to buy.
 
Beware of the after market manuals on some of their details. The center main journal changed sizes in 1979, but the rod journals have been the same size since 1974. They were smaller in 1973. There is no need to bore a cylinder that is in good shape & within spec! This is not a car engine. We call this saving "Cast Iron" in the industry. You can't get it back. God forbid if you have a problem & the motor needed to be cleaned up on a cylinder again you won't have any left. This engine has pistons available in .020, .030, .040, & larger. It is the 350 Chevy of the industry. If you don't have a bore shop near you who does marine engines (they are different - blind holes) then there is one in Sparta, TN. Jays Block Shop. Shipping just the back half of your block is easy & affordable. Honest & affordable guy. Can sell you parts or you can get your own.

Dan in TN
 
Thanks Dan. I'll keep Jay's block shop in mind.

Looking at eh specs again I see I have .001 of tolerance. I'm within the max min spec on all cylinders even though I have have .0005 to ,001 of out of round. If this were a DD car motor I would not think twice about doing a glaze breaking hone and moving on but was not sure this holds true for a two stroke. The design is really foreign to me. the shape of the pistons is one thing and understandable but the top compression ring is super high and the bearing tolerances are super tight so was not sure if the bore size was super critical as well.
 
I said you didn't have to bore all cylinders, but you should change ALL pistons! You have high ring pistons that need to be changed. Pistons are the wear item in outboards because of the dow pins (locate the rings). These get loose in the pistons over time (especially if over heated) and fall out. The rings then can rotate. When they reach a port they get clipped. That is the number failure mode for two stroke motor till this day! Do not be tempted to reuse your old pistons. Someone who is familiar with outboard rebuilding can measure your motor & advise you as to what needs to be done.

Dan in TN
 
The motor is close to 40 years old if you do the rebuild correct it should never need to be rebuilt again anyways. My concern is not the bore but the weight of the pistons at 5500rpms can make or break a rebuild. Maybe take a dremel to the insides of the skirt on the larger piston to balance the crank. It don`t take much to shake the motor apart.
 
Also measure the bottom of the skirts. Piston to cylinder clearance is real important normally between .0018-.004 the tighter the better for crankcase precharge.
 
t2stroke said:
I said you didn't have to bore all cylinders, but you should change ALL pistons! You have high ring pistons that need to be changed. Pistons are the wear item in outboards because of the dow pins (locate the rings). These get loose in the pistons over time (especially if over heated) and fall out. The rings then can rotate. When they reach a port they get clipped. That is the number failure mode for two stroke motor till this day! Do not be tempted to reuse your old pistons. Someone who is familiar with outboard rebuilding can measure your motor & advise you as to what needs to be done.

Dan in TN
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Great information!!! This I'm sure is what happened on my one bad hole. Did a search for Jay's block shop and came up basically empty. I found a phone number on forum in a post from over a year ago. I'll have to call them to see what's doing as I'm having no luck locally.
 
kimcrwbr1 said:
The motor is close to 40 years old if you do the rebuild correct it should never need to be rebuilt again anyways. My concern is not the bore but the weight of the pistons at 5500rpms can make or break a rebuild. Maybe take a dremel to the insides of the skirt on the larger piston to balance the crank. It don`t take much to shake the motor apart.
Click to expand...

i can balance the pistons. Have the scale and tools. I've done this plenty with car engines. As long as there is some meat at the wrist pin it should be no issue. An advantage is it's a flat plane crank so the imbalance is not as pronounced as with a cross plane crank.
 
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