Help me to re-ring my engine.

[crispins]

I am trying to understand my boat fully.

Can someone tell me what this part is (not my boat) ?

 

[racerone]

The " wet muffler " is what it is.

 

[crispins]

I am going to pull the other head off today, clean all cylinders, and take pictures with my better camera so I can get your opnions.

As of right now wore out rings is the only thing that explains the low compression that is unless the head gasket is not holding a seal correctly but no one has said that the gasket did not look good.

 

[racerone]

???---You need to understand / look at the type of piston ring in the top groove !---Those rings really wear out the groove in the piston !---And I have looked at those grooves with a microscope.----I have knowledge on these motors that goes way beyond changing sparkplugs.

 

[Tim Frank]

I am going to pull the other head off today, clean all cylinders, and take pictures with my better camera so I can get your opnions.


As of right now wore out rings is the only thing that explains the low compression that is unless the head gasket is not holding a seal correctly but no one has said that the gasket did not look good.

This is a bit like a paint job, which is only as good as the preparation that you do. People often want to get to paint application ASAP and skimp/rush the prep.
You are just dying to get at the rings and get this done quickly. My suggestion is : do the prep/diagnosis properly.

Post 8 questions the compression test and tester. That should be verified with a known-good gauge. An "autozone loaner" of "uncertain quality" should not be the very base block of a major project. At least IMO.

As far as assessing a head gasket from a picture....if you cannot assess it first-hand, I am not sure why you would expect it to accurately evaluated from a pic.

 

[crispins]

???---You need to understand / look at the type of piston ring in the top groove !---Those rings really wear out the groove in the piston !---And I have looked at those grooves with a microscope.----I have knowledge on these motors that goes way beyond changing sparkplugs.

So are you saying reusing the old pistons is not very likely?

Can you explain why?

 

[crispins]

I took the other head off today.

I removed the cowl which makes working on the engine so much easier.

Anyway the top cylinder has dents on the piston and head most likely from a piece of ring that got broke off. Cylinder is in pretty good shape with just one scratch in it.

Looking at the head gasket from the other side (port) I can see that the top cylinder gasket seal was blown.

So my idea is to replace the one bad piston and head and instal new rings.

Racerone I think is saying that the pistons cannot be re-ringed, does anyone else feel the same way?

Here are some pictures

BAD CYLINDER STARBOARD SIDE



SAME HEAD BOTTOM CYLINDER



PORT SIDE BLOWN HEAD GASKET



BAD PISTON



BAD PISTON BUT CYLINDER LOOKS GOOD

 

[Tim Frank]

So are you saying reusing the old pistons is not very likely?

Can you explain why?

That is what Racerone is saying.It is in his post.
The square milled grooves in the pistons tend to wear and the rings do not fit properly any longer. It is not easy to measure to see whether they are still within spec.

 

[jakedaawg]

Time for a complete teardown/rebuild. You will need to measure all bores and journals and such. Might as well do it right. Yes, you will want to replace the pistons. The head will be fine just use a magnet to make sure there are no pieces of ring imbeded in the Al.

 

[racerone]

???----If pistons are original it is the triangular groove for the top ring that is the problem !!----As I stated very clearly before , you need to have this motor apart on the work bench.----Then inspect / measure the parts.----Plan a repair.-----Guessing / assuming does NOT WORK on these motors !---------Most of all you need to find out why the one piston ran so hot !-------Fix that issue.-----------Or you will be doing the job a second time.---------Bonus, it will not take you as long the second time.

 

[77kingfisher]

Bonus, it will not take you as long the second time.

Or the third or fourth depends on your tool kit and mechanical aptitude.

 

[interalian]

The bad piston looks to have serious erosion on the deflector/crown area that isn't related to ring impact. Heat, water or a combination due to the gasket failure. But waterjacket and water diverter rubbers could have contributed. Regardless of what you're planning, this motor will need to be torn down fully in order to determine why it died (as stated earlier).

http://s139.photobucket.com/user/crispincrispin/media/Jet Boat/CIMG4647.jpg.html

 

[crispins]

Well this does not seem encouraging.

Full rebuild kit is around $1,400
Machine work I would guess $300
Misc tools / gaskets $300

We are at $2,000 already.

 

[flyingscott]

That rebuild kit is to high you should be able to rebuild that motor yourself for around $1100. Try this kit comes with everything. http://www.ebay.com/itm/Johnson-Evi...ash=item58b8ba9a70:g:c~AAAOxy4fVTBgwl&vxp=mtr

 

[crispins]

OK - the motor is getting a full rebuild.

Do aftermarket pistons solve the ring spitting issue these motors have?

Are there any easy performance increases to be had during the rebuild?

 

[interalian]

At 115, this engine is pretty much maxxed now.

 

[nanuk]

one thing I learned about 2stroke engines... standard auto compression testers do not work well, you need one that has the schrader valve at the plug end of the unit.

 

[crispins]

Well I brought the boat to a rebuilder.

I am getting the engine rebuilt, carbs redone, and the boat lake tested.

Cylinders bored, new Wisco pistons, all new bearings and gaskets plus a new used head.

Should be done in around 3 weeks.

 

[crispins]

I chose to have the engine fully rebuilt.

Was bored .0020 over, Wisco pistons, lake tested.

Picking it up in the morning

Can't wait to take it out, I know I need to break in the engine properly first.

 

[Faztbullet]

Run it for several RPM cycles and then shut if off and complexly cool several times to temper the pistons. Siezco pistons as soft till they temper up and make sure engine is at temp before running WOTeven after break-in