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The REAL cost of partly-rebuilding an older engine (Johnson 85 1979)

M

Mz3bo

New member
Hello Friends,

As you saw in my previous post, my 1979 Johnson 85 is having 1 piston with low compression (90 - 120 -120 - 120) but is still running Strong ! I have read a many site about it's not worth rebuilding it because of cost etc.. some even approached a 2500-4000$ estimate cost to fully rebuild the motor.

My question is, as a DIYer, what can be the real, not exagerting cost of PARTLY- rebuilding such engine, especially for my personnal case. This is what I came with by looking at the parts diagram. Of course, I will be doing this myself

To my understanding, these parts has to be changed and cannot be reused:

1- 4 pistons with ring and wristpin and all clips (wiseco are $56 per kit per piston)
2- 4x rebore if necessary (not sure yet it will be necessary, maybe just rehone)
3- 4x wrist pin bearing
4- All gasket exposed while opening up the engine
5- few oring here and there and seals....

These parts, to my understanding, can be reused:

1- 4 Connecting rods
2- crankcase head bearing assemble
3- Nuts, bolts and washer that are not damaged
4- Crank ! (should be good)

Considering I have done all this so far during the last months:

1- Carbs rebuild
2- new starter
3- New CD2
4- New coils pack
5- New fuel pump
6- New plugs
7- New thermostat
8- New waterpump
9- new stator power invertor (can't remember the real name)


What do you guys think. Am I missing something Really big that can overcome my little project ? Any help would be greatly appreciated !

Thanks
Bo
 
#2 Today, 07:28 PM

I myself don't like the Seizeco pistons as they require extra clearance,need to go thru several heat cycles to temper piston and you have to allow engine to reach temp before WOT throttle operation but they do run OK in a worn hole. Go with a WSM piston as only $13 more and you will need a tube of gelseal and primer..Since your going to have to do block work just find a 140 block with pot belly and put the new pistons and you stuff in it. Then you have a good 115hp motor.
 
90 psi on one cylinder to me dont sound like rings it could be just a head gasket. I would just pull the heads and look at the cylinder walls for scoring. Pull the bypass covers and exhaust covers carefully press on the rings if a ring dont spring back its bad. If the rings are good and you dont see scoring on the cylinder walls put on new head gaskets and do the compression test again. A little over 35 bucks for head gaskets to find out if you need to do a ring job. You will see any damage to the pistons with the exhaust and bypass covers off. Take pics and show us what you find.
 
kimcrwbr1 said:
90 psi on one cylinder to me dont sound like rings it could be just a head gasket. I would just pull the heads and look at the cylinder walls for scoring. Pull the bypass covers and exhaust covers carefully press on the rings if a ring dont spring back its bad. If the rings are good and you dont see scoring on the cylinder walls put on new head gaskets and do the compression test again. A little over 35 bucks for head gaskets to find out if you need to do a ring job. You will see any damage to the pistons with the exhaust and bypass covers off. Take pics and show us what you find.
Click to expand...

Hi,

Thanks for the answer... the piston are damaged... check for my previous post and you will see the pictures links....
 
You cannot put it back together like it is. You may as well break it all the way down and make up a parts list on what needs replaced first and make your decision from there. Factor in the gearbox condition you may as well do a reseal as well if you put the time/money into the engine.
 
http://cgi.ebay.com/ebaymotors/Engi...214003?hash=item360a8c8033:g:A20AAOSwGzlTvUeP
After you pull the crank see how easy you can clean up the cylinders. Use lots of oil and get a nice cross hatch and take away any glazing. time the amout spent on all the cylinders the same put one of the old rings in the bore and measure the gap top middle and bottom. You may get away with standard pistons and rings
http://cgi.ebay.com/ebaymotors/3-1-...720210?hash=item51ee5245d2:g:uY8AAOSwwbdWLudl
Never use one of these hones on a two stroke it deforms the cylinders around the ports.
 
Ring end gap should be between .07-.17
Piston clearance is most important here .0045- .0075
According to my book the old pistons were prone to failure due to the short distance from the top of the piston to the first ring the new pistons should be about twice as far from the top of the piston.
 
1) You never use a spring hone as it will follow a out of round cylinder and diesel fuel is best honing fluid.. use a rigid hone only as it will show if cylinder is out of round or wear around ports as the worn area will leave a shadow.
2) A ball hone wont deform ports but the balls can break off and hide in a port which is reason cleaning is SUPER important. Merc/BRP use ball hones on their engines on Etec/DFI engines and so do all the engine reman companys and myself included. Most rebuilds fail due to improper cleaning of honing/boring debris and that hone listed wont work its not for a cast iron cylinder.....
3) You measure ring gaps with NEW rings not old worn rings after you mike the cylinders and find out what size piston/rings you need and you cannot put oversize rings on a stock piston no matter what you read, All ways use a ring expander to install them on piston and use a ring compressor to install them in cylinder not a screwdriver.
 
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The cylinder heads have small steel particles embedded within them. Believe me when I say that it is just about impossible to remove those particles. One small piece missed will result in having that speck of steel glowing like the glow plug of a model airplane engine, and this in turn will result in a pre-ignition situation (combustion taking place before the specified timing degree), which will, again in turn, result in melted pistons within a short period of time.

Bottom line.... figure on replacing those cylinder heads!
 
His pics from the other post show the pistons to have some sort of heat damage. There is serious reddish discoloration on one, and the other is sorta showing it.

So, I looked at the water deflector...and it looks good to me.

What, in you guys' opinion, is the original cause of this heat damage and ring failure on this engine?
 
Partly rebuilding means you have only partly inspected the engine. As suggested, you really need to break down the entire engine and go through all bearings and surfaces. Check end play on the connecting rods to make sure they are okay and inspect crank bearings. All new seals are a must as well as gaskets and deflectors.

As JoeReeves suggested, you really need to get new heads. You could possibly use a die grinder and smooth out all the high spots but any bits of steel left over could act as a glow plug.

Use WSM pistons for sure, not Wiseco. Also, before you buy any parts or hone the cylinders you need to mic them and check for roundness and taper. Get the cylinders right before you get pistons.

KJ
 
Would you not think that WISECO would make changes / improvements on their pistons ??----------How many years have they made pistons ?---------How many pistons do they make every year.--------I use them with no problems.
 
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