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Johnson faststrike 150 rebuild

J

Jberry

New member
I have a 97 model fast strike 150 that has been a great motor, but a couple days ago I noticed a knocking sound while running. I did a compression test and the top 4 cylinders are around 110 but the bottom 2 are 85 and 95!! So I guess it is time to do something. How hard is it to rebuild one of these, I would like to do some of it myself to save a little money. Is it possible that it just needs a new ring job? Or is it most likely need to be bored out??just looking for thoughts!
 
Sounds like you definitely have a problem with the 85 lb. cylinder. These motors have staggered combustion chambers & compression is lower on #5 & #6. You might see as much as 10 lbs, but 25 is too much. I would suggest you pull that head & take a look. Not hard to do & the motor has o-rings instead of a head gasket. They are reusable. Just need RTV to seal the water passages in the block from external leaks.
Rebuilds are not hard if you are mechanical minded? The motor will probably need attention on that questionable cylinder. If the motor has never been over heated then good chance the cylinders are still round.
 
Thanks, I am fairly mechanically inclines, so I will prob attempt it myself, and I don’t think it has ever been over heated, could it just need new rings?
 
If you decide to rebuild the motor have the block pressure tested before anything. You need to rule out the casting flaw that appears in some of those blocks.
 
Should I get it pressure tested before I pull the head to look at pistons? Never had a pressure test on one before!
 
Yes find someone to pressure test the block. The V6 loopers sometimes have a casting flaw from bad mold alignment when they are cast. If you have one of those blocks it will be less expensive to replace it. Early blocks had it the worst but the flaw can show up in later blocks.
 
I would pull the head on the 85 lb side. I think you will see a problem with that piston. I do not think rings will fix this problem on that cylinder. All of the motors we pressure tested were always taken apart. They were being rebuilt anyway. You have to seal the head areas, bottom & top of block (where you add the air pressure). You filled the block with water & the 100 lbs of air cause the water to leak. You can see water so you know where the leak is. It is a straight forward repair at that point.
 
Just out of curiosity, when I pull the head, what are things that I will be looking for on those two pistons?? Burnt tops? Grooves in the cylinder walls? Trying to get prepared before I pull them.
 
I think the 85lb hole should be obvious. You could see any of the things mentioned or a dished top of a piston. I would expect scoring of the cylinder walls which would require boring, but you might get lucky. You still need to measure the cylinder for out of round or wear. This particular model is not bad for that unless it has been over heated.
 
So I took the head off and I really can’t seem to see the problem, the piston head is black colored, but the cylinder walls appear to be really smooth with no grooves? I took pics but I don’t know how to upload them? Any idea how to upload the pics and I will get them up
 
Click the icon with the tree on it
2DB220F3-5DCF-4EB5-9E30-5CAC903D06C4.jpeg
Click the tab that says From Computer then click Choose File.

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You should now see a screen that asks where to get the images.
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Go to your library, take a picture, or browse for wherever you have them, and select the picture you want. You’ll come back to the Insert Image screen and your photo should appear in the line next to the choose file button. Next click the words Upload File(s) and the photo should appear in the reply box. That’s kind of the odd part because on phones it’s not clear that you have to press the words Upload File. I think on the computer version that is a button.
 
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So I’m doing all of that, the photo does appear next to the choose file button, but when I hit the upload file button, the photo goes away and does not come up in the box?? Any idea??
 
Hmm, not sure. You might need to contact an admin. That is the exact sequence I used to post those screen shots and it worked fine.
 
Ok, I pulled both heads off, there is no visible signs of any problems! There is carbon build up on the pistons, but it’s equal on all of them. The pistons don’t seem to have any slack in them. But the bottom two cylinders are lower compression! Could this be a reed valve broke on that bottom carburetor?
 
Also I had a machinest buddy of mine miked the cylinder walls and he said they are within a thousandth of the standard bore and said there was no issue with the cylinders!
 
If its knocking and low on compression you have a problem...damage could be in skirt area you cannot see until piston is removed. I have seen several of these motors with cracked piston skirts that caused knocks.
 
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