Weird JW compression test.

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Tubs
Posts: 1809
Joined: Thu Mar 12, 2015 7:47 am

Re: Weird JW compression test.

Postby Tubs » Fri Jul 13, 2018 9:41 pm

Crank shaft seals?
What is the motor were working on?
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cajuncook1
Posts: 606
Joined: Mon Mar 09, 2015 10:05 am
Location: DFW, Texas

Re: Weird JW compression test.

Postby cajuncook1 » Fri Jul 13, 2018 10:26 pm

Tubs wrote:Crank shaft seals?
What is the motor were working on?



Tubs, based on the title of the post, I think he is working on a Johnson JW 3hp. Year, not sure. Love working on those little rascals.

Cajun

Stanley
Posts: 265
Joined: Tue Mar 10, 2015 9:21 pm

Re: Weird JW compression test.

Postby Stanley » Fri Jul 13, 2018 10:30 pm

Yes a JW13.Simple reliable and easy to work on.I've rebuilt 3 others with no problems other than the usual.This one is a stumper.

FrankR
Posts: 3459
Joined: Tue Mar 10, 2015 6:32 pm
Location: Florida

Re: Weird JW compression test.

Postby FrankR » Sat Jul 14, 2018 3:23 am

Exhaust obstructions are something to consider. Especially the above-water exhaust relief ports. Those have a profound influence on starting and idle. That is one reason why a worn out motor may start on the stand but not in the water.

FrankR
Posts: 3459
Joined: Tue Mar 10, 2015 6:32 pm
Location: Florida

Re: Weird JW compression test.

Postby FrankR » Sat Jul 14, 2018 3:29 am

I had a Lightwin 3 that drove me crazy for way too long. Compression was acceptable but hard start, poor idle and less than normal power. Finally, I discovered the pistons were installed backwards by some previous owner.

BillW
Posts: 897
Joined: Sat Apr 11, 2015 6:35 pm
Location: Cape Cod MA

Re: Weird JW compression test.

Postby BillW » Sun Jul 15, 2018 6:03 am

I just had a 3 hp Lightwin that had some binding in the gear case. I noticed it before ever trying to start it; however, I was just thinking that if one of your 3s had more mechanical binding somewhere than the other, it could result in no/bad idle, hard start and even lower compression with an electric drill. Just speculating that maybe you're stronger than the drill, when pulling by hand, giving the slightly higher number? Dunno, just a thought.


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