1987 50hp Johnson problem

[Rad2101]

Hi all,

Trouble with a 2 cylinder 1987 50HP Johnson. Any advice please.

Picked motor up as a cheap motor needing some work. Seems to start and run ok, pumps water out the pee hole. After running for maybe 5mins on trolly in idle with muffs seems to be getting very hot. (cant hold hand on heads for more than 5 secs). Did a compression check when warm and found top cylinder 130psi, bottom cyclinder 110psi dry and top cylinder 145psi, bottom 125psi wet. So about 30psi difference between top and bottom in both cases.

Does this sound like multiple problems, head gasket, cooling problem or both? How hot should it run and would I get away with the compression results?

Is there a way to blow/clean out the water jacket, thermostat etc without removing the head?

Any further advice before I jump on in and remove head much appreciated.

Many thanks

 

[boobie]

Re: 1987 50hp Johnson problem

First thing to do is pull the head and check the head gasket and cyl's with the different compression you have. Next thing to do is replace the water pump impeller.

 

[bonz_d]

Re: 1987 50hp Johnson problem

Sounds to me as though there are stuck rings on that low cylinder. Also on mufffs it shouldn't get that hot. As advised pull head and check for blocked water passages. Then try a decarb after it's running again with SeaFoam.

 

[Rad2101]

Re: 1987 50hp Johnson problem

Thanks guys for your reply. Was hoping the commpression would be just on the edge and I might get away with blowing out the water channel. What is the spec for compression? I will drop lower unit and check pump housing and impeller, get the cylinder head off and see what I need. Can I do the head without removing the whole power head? (1987 50Hp model J50TLCUD).

Many thanks much appreciated

 

[Rad2101]

Re: 1987 50hp Johnson problem

Hey guys, Sorry to ask again but I had no further response. Can I remove the cylinder head without removing the whole power head? (1987 50Hp model J50TLCUD). What is the spec for compression on this motor?

Cheers

 

[bonz_d]

Re: 1987 50hp Johnson problem

Yes you should be able to remove the head only. As to compression there is no set point as there are way too many veriables. Gauge reading very a lot between different gauges even on the same enigine. Cranking rate/speed will have an impact as will temps. Though anything below 90psi is thought to be weak. More important is to see an even range between cylinders. Normally not more than 10% as that usually indicates damage or some stuck rings.

Now I just recently picked up a 1975 50hp Johnson that is reading 150psi on both cylinders. Almost new!

 

[JB]

Re: 1987 50hp Johnson problem

Please do not remove the head or anything else until after you have done a new impeller, a decarb and a full link 'n' synch. A 20# difference (not 30#) does not suggest a serious compression problem but there is a problem. It could be causing temperature control symptoms.

Non-invasive procedures should always be done before any dismantling.

Let us know what you get.

 

[Rad2101]

Re: 1987 50hp Johnson problem

Many thanks again guys. As advised I will check everything else before I jump in and dismantle. Got a feeling I will have to dismantle still but well worth doing the impellor and decarb etc first Better get a manual and a few parts and see how it goes.

Can you recommend a decent manual? I've read a few names this forum but not sure which ones were the good ones.

I'll let you know how I go. Cheers

 

[bonz_d]

Re: 1987 50hp Johnson problem

The best and only ones worth getting are the original OMC service manuals. Some times they can be found used on ebay otherwise through Ken Cook new.

 

[Rad2101]

Re: 1987 50hp Johnson problem

Thanks again. Ken Cook has the manual for my model unfortunatley the shipping costs to Australia are more than double the cost of the manual. $170 AUD. I'll see if I can find something locally. Are the Seloc ones any good if I have no luck?

cheers

 

[bonz_d]

Re: 1987 50hp Johnson problem

I still think ebay is the way to go and then have it sent through the post office and not UPS,FedEx or DHL.. Then if you can find a seller willing to work with you it's even cheaper to send through the post office if it is sent book post.

 

[carholme]

Re: 1987 50hp Johnson problem

To get you started until you get the OEM manual, here is a link to the condensed version of the Clymer manual. Download it soonest to your computer as the link is short lived.

Small Engine Repair Reference Center Home

Parts listing for J50TLCUD:

1987 Johnson/Evinrude 50 - OMC, Evinrude & Johnson Parts Lookup

Gerry

 

[Rad2101]

Re: 1987 50hp Johnson problem

Thanks again for all your input. I have downloaded this condensed manual and will keep an eye out for an OEM version locally. This might be enough to get me going.

If I have no luck in sourcing an original what would be the next best thing? Seloc? Clymer? Something else.

cheers

 

[Rad2101]

Re: 1987 50hp Johnson problem

Just an update on this old motor.

Got the manual, did the decarb, impellor, link and sync. No difference. Decided to pull the cylinder head. Check water jacket etc.

Top cylinder was all good, bore was smooth and no signs of wear. Bottom cylinder not so good. Signs of wear and scoring to bore. Time to pull the power head. Hoping a hone and new rings might be enough.

After much swearing and snapped bolts got the head off. Pulled it down, removed crankcase and pistons.


Damage was much worse than I thought. Top cylinder was very good Hardly any signs of wear and rings looked free and ok. Bottom cylinder however showed extensive damage to bore and piston. Bottom ring stuck bad and worn.

I have shopped around my area and can get the engine block bored and honed for a reasonable price. Will need to aquire at least one oversize piston and rings. So I'm planning to keep going on this.

What is the feeling about only doing one cylinder? What else should I be looking at replacing while I have the thing apart? Bearings etc?

Many thanks cheers

 

[Bosunsmate]

Re: 1987 50hp Johnson problem

Im not sure about doing just one cylinder, ive heard people say you have to do all. Im sure people do do just one cylinder though. I will be interested in what is said.
Id do the big end bearings and conrod screws. Also the upper and lower seals and check the upper and lower bearings for any play or a bearing that isnt quiet when spun.

Also after reading this post you said it was peeing. Peeing can for some people mean a dribble. If a motor isnt peeing like a dog on its first **** of the day then i consider there to be something wrong

 

[Bosunsmate]

Re: 1987 50hp Johnson problem

If you had a bit of spare cash to put into it id get new rings for the top cylinder too if you keep that piston and dont up size.

 

[Rad2101]

Re: 1987 50hp Johnson problem

Thanks for the advice once again. I will replace bearings and seals also.

Just looking through the manual and it does mention "it is permissable to have one or more oversize pistons in an engine". Obviously to keep costs down this is better. One bore and piston are very good still. Will still put new rings on both. Just wondering what the general concensus is regarding this. Is it better to do both? Is there any disadvantage in only doing one?

As far as the peeing goes, it does or did pee pretty hard when it was running. While I have it apart I will clean out the water channels and replace thermostat etc. Still dont know why it was getting so hot. Have been thinking the heat may have caused the failure to start with.

Another question. I will need to re bore one cylinder at least and I have found in the manual the first Over Size piston is 0.030". I have also found 0.020" O/S that appear to me to be the same and say they will fit from Sierra and Mallory etc. If I can get away with boring out to 0.020" would these pistons be suitable?

Thanks guys

 

[Rad2101]

Re: 1987 50hp Johnson problem

Before I go ahead with any of this machine work. Any further thoughts on doing one piston oversize. Or which size O/S to go to or piston manufacturer?

Many thanks

 

[Bosunsmate]

Re: 1987 50hp Johnson problem

I cant add anything more than to say if the manual says it ok then id take that advice pretty well to be accurate.
Ive used many Sierra parts so if you can get away with boring out less then that would be what id do. Get them to check the bore at the lower value to see if thatd do then order your piston.
Ive never used a Mallory part as my supplier doesnt stock them

 

[Silvertip]

Re: 1987 50hp Johnson problem

I didn't see if you pulled the thermostat to see if it was stuck shut which is a prime cause for overheating. After your rebuild be sure to replace it regardless of its condition. You are advised to also do a carb rebuild. Chances are the cause of the failure was either a lean condition due to a carb issue, or an overheat due to bad water pump or the thermostat. Yes -- you probably saw water exiting the tell-tale. But think about it. House water pressure was forcing water through the engine, not the water pump which also could have caused the failure.