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Thread: 2 cycle combustion chamber repair

  1. #11

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    Have you tried the old wood workers method of taping the back side of the finer grade sand paper with duct tape? This will help keep the paper cool, wear less and remain wrinkle free. Also, you might look into a different paper. Some of the ones I use are rather thick to begin with regardless of how high I go. I run up to 600 before I get into cloth. Hope this helps. Good. luck, thanks for sharing.

  2. #12

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    I'm liking the idea of gluing radial stops of whichever-grit-you-want cloth or paper to the resin form. Essentially making your own custom flap wheel. That's a great idea. Just copy the method all the big manufacturers use:; epoxy glue like JB Weld and emery cloth strips.

  3. #13

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    That is Detonation from using either Old Gas, or Low Octane Gas for your Compression Ratio used. What CR Ratio are you running? For most Stock 2 Strokes you need 91+ Octane, if it's CR has been altered higher you probably need an even Higher Octane. Did you do a Cranking Compression Test, if so what psi was it? Did you do a Squish Band test to see what it was, if so what?

    Pump Gas can loose 2 Points in Octane in as little as 2 Weeks. 100LL Aviation Fuel has a 5 year shelf life.

    There is different ways to fix your head.
    1. Weld up Chamber and re-machine.
    2. Machine Bottom and re-cut Chamber till cleaned up.
    3. Machine Head for Inserts like most Billet Heads use.
    4. Sell your Stock Head and Buy a Billet Head.

    I have bought NOS Billet Seadoo Heads off eBay for $29 to $75.

    Just my 2 cents!

  4. #14
    hemmjo's Avatar
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    hemmjo's Tools
    Quote Originally Posted by Armilite View Post
    That is Detonation from using either Old Gas, or Low Octane Gas for your Compression Ratio used.....
    Armilite.. Thanks for your input, but this damage it not from detonation. I am sure you will agree if you look close. I did do a compression test when I installed it, 120 in both, which is 30 pounds low. I have learned since this incident that the company involved cuts chambers to reduce compression to avoid warranty claims from people using cheap fuel.
    2 cycle combustion chamber repair-head-close.jpg
    You can see the perfectly round impressions left by ends of the steel pins. The irregular shaped impressions were caused by bits of aluminum that were scrapped from the crankcase as the pins were forced between the crank and the case during their violent escape out of the engine and into the lake!

    The damage was caused when two bearing alignment pics worked their way out of the crank bearings because the case halves were held apart by an oversized thrust ring that was installed by a big name PWC engine rebuilder. Whoever assembled the engine HAD to know they had something wrong as there was WAY too much sealant between the case halves.
    2 cycle combustion chamber repair-missing-pins.jpg

    I would not have even known the pins came out if one had not smashed the sparkplug closed. While it did run rough for a few seconds, I thought I had sucked up a stick or mud as I was running slow in the no wake zone. The second pin came out at speed and it instantly began running on one cylinder.

    I did contact that builder even though the engine was out of warranty, assuming they might want to know what they were installing incorrect parts. Thinking I might able to save someone else this aggravation. Due to their indignant response to the well documented obvious error, I will never purchase another part from them.

    The engine is from a 1998 TigerShark TS770L. It is one from a pair of identical boats that I bought from a guy who asked me to repair them. One had been run with no oil, the other had been damaged from improper winterizing. When I gave him the $4000.00 estimate to replace the engines and broken exhaust manifold in his boats, he sold them to me cheap. Since the complete rebuilt engine was only $20.00 more than all of the parts it would take to rebuild it correctly, I opted to purchase it rebuilt. My mistake!!! I rebuilt the second engine myself as it was not hurt as badly. It is running just fine and was in fact quicker than the rebuilt one.

    I always use fresh Sunoco Ultra 93 octane fuel in my boats, then use whatever is left over over in my truck at the end of the season.

    John

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    Thanks hemmjo! We've added your Combustion Chamber Polishing Tool to our Engine category,
    as well as to your builder page: hemmjo's Homemade Tools. Your receipt:




  6. #16

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    Quote Originally Posted by hemmjo View Post
    Armilite.. Thanks for your input, but this damage it not from detonation. I am sure you will agree if you look close. I did do a compression test when I installed it, 120 in both, which is 30 pounds low. I have learned since this incident that the company involved cuts chambers to reduce compression to avoid warranty claims from people using cheap fuel.
    Click image for larger version. 

Name:	head close.jpg 
Views:	45 
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ID:	18745
    You can see the perfectly round impressions left by ends of the steel pins. The irregular shaped impressions were caused by bits of aluminum that were scrapped from the crankcase as the pins were forced between the crank and the case during their violent escape out of the engine and into the lake!

    The damage was caused when two bearing alignment pics worked their way out of the crank bearings because the case halves were held apart by an oversized thrust ring that was installed by a big name PWC engine rebuilder. Whoever assembled the engine HAD to know they had something wrong as there was WAY too much sealant between the case halves.
    Click image for larger version. 

Name:	missing pins.jpg 
Views:	77 
Size:	322.9 KB 
ID:	18744

    I would not have even known the pins came out if one had not smashed the sparkplug closed. While it did run rough for a few seconds, I thought I had sucked up a stick or mud as I was running slow in the no wake zone. The second pin came out at speed and it instantly began running on one cylinder.

    I did contact that builder even though the engine was out of warranty, assuming they might want to know what they were installing incorrect parts. Thinking I might able to save someone else this aggravation. Due to their indignant response to the well documented obvious error, I will never purchase another part from them.

    The engine is from a 1998 TigerShark TS770L. It is one from a pair of identical boats that I bought from a guy who asked me to repair them. One had been run with no oil, the other had been damaged from improper winterizing. When I gave him the $4000.00 estimate to replace the engines and broken exhaust manifold in his boats, he sold them to me cheap. Since the complete rebuilt engine was only $20.00 more than all of the parts it would take to rebuild it correctly, I opted to purchase it rebuilt. My mistake!!! I rebuilt the second engine myself as it was not hurt as badly. It is running just fine and was in fact quicker than the rebuilt one.

    I always use fresh Sunoco Ultra 93 octane fuel in my boats, then use whatever is left over over in my truck at the end of the season.

    John
    =========================================================

    John:

    I agree the Thrust Ring looks over sized in the photo but they usually have a slit/gap where they compress once the Case is bolted together. Those Pins coming out of the Bearings is a Mechanical failure, and are for keeping the Bearing from Spinning in the Case and are Hardened Steel. Since you seem to know How to rebuild an engine, Why did you not take it back, once you knew there was a 30psi difference from what a New Engine should be at? If they did Mill the Head and not re-cut the Squish Band right you can still have Detonation issues even with 93. I agree a pin could have come through, but I think you still had some Detonation issues also. The Engine did make Warranty, what was that? You should have taken it back as soon as you new about the CR issue. What Brand of Bearings did they use? Did they rebuild the Crank or was them old Bearings? Lesson learned, always do your own work.

    Rich


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