Engine teardown - reed screws for lunch

[mn_reeds]

Quick background - engine is a 61x/62t that has 19 hours on the clock since a full rebuild with a new crank from JM.

Was out riding and dropped power but made it back to shore. Pulled it into the garage and started troubleshooting. Compression check passed initially (190/190), went through fuel system, one of the spark plug boots was marginal so I dropped in a new yamaski coil. I then pulled the head for a quick visual and both pistons looked good. Re-assembled the ADA with new o-rings and then proceeded to see if the new coil fixed it.

Ski started but was still not running properly. Back to compression test again and had issues front -190 and rear 170. Figured I had pinched an o-ring so pulled the head again and found a new ding from just the 30-45 second of run time :



Time for a full teardown to see what is going on. Turns out that both screws from a reed stop had backed out and went through the rear cylinder. Damage to top of piston and top ring.




The cylinder itself seems to have survived with no scaring or groves:




If the bottom end/crank checks out can I just get a new piston and be back in action? I do run a b-pipe but will flush that if I don't find the other screw in the cases.

The reeds came with the previous motor but I did check all of the screws prior to re-using them. What would have caused those screws to back out? Do I need to pull all of the screws and drop some blue loctite on them? Actually were they even assembled correctly since they already had the carbon fiber pedal limiter?

Any other insights or things to look out for?

 

[Sanoman]

Can’t answer your questions, but you got lucky on this one!

 

[long beach local]

I would definitely use loctite on those threads. The crank is probably ok i bet I have broken reeds before and ran it without doing a bottom end. But it’s up to you If everything spins quietly new pistons and back on the water.

 

[fastgtfairlane]

Very hard to tell from pictures alone but it looks like the there is a score in the bore on the rear cylinder. If you can catch your fingernail on the score mark ,then a new bore and pistons would be required.

 

[Sparkplug]

Depending your piston clearance. You can hone it with the proper type hone and slap a new piston and ring set in. I just did it to a motor and have put about 10 hours on it.

Just measure it and see how much you can take off and still be in spec.

 

[mn_reeds]

Appreciate the responses. I've double checked the cylinder and there aren't any places that catch a nail above the ports - just some scuffing. However it looks like part of a screw lodged just below the boost port and that definitely catches a nail but is raised and not a scratch.

You can see the little dot in the picture below and it is roughly 14.5mm down. Since it's below the port is that something that could be honed out? This 61x cylinder is on it's last bore at 84mm so would have to be re-sleeved.



Does anyone know what kind of reeds these are? I haven't been able to find a two stage carbon reed like this online. Was thinking carbon tech or boysen super stock but they don't seem to match up.

 

[aboarder]

Use red locktite on screws like that. If you tried turning the screws when you checked them, you could have cracked the hardened locktite. In that case, pull and clean all the screws, put a dab of new red locktite on, then reinstall. Red is best for screws on the reeds and carb butterfly, which won't be coming out very often and it's really important that they don't back out.

 

[long beach local]

Appreciate the responses. I've double checked the cylinder and there aren't any places that catch a nail above the ports - just some scuffing. However it looks like part of a screw lodged just below the boost port and that definitely catches a nail but is raised and not a scratch.

You can see the little dot in the picture below and it is roughly 14.5mm down. Since it's below the port is that something that could be honed out? This 61x cylinder is on it's last bore at 84mm so would have to be re-sleeved.

View attachment 439377

Does anyone know what kind of reeds these are? I haven't been able to find a two stage carbon reed like this online. Was thinking carbon tech or boysen super stock but they don't seem to match up.

If you’re going to hone it I would get that little burr smoothed out first roll up a small piece of wet/dry sandpaper 220 or whatever and make sure there is nothing to catch a ring and it’s all smooth chamfered etc take your time and be meticulous saving that cylinder.

 

[mn_reeds]

Thought I would post some updates on the cylinder. My first attempts to remove the piece of screw lodged in the sleeve with just sandpaper didn't even make a dent. I was able to make some headway with a tiny flat pick but there was still a little remaining that had to come out. It sounds pretty aggressive but I ended up using a carbide burr on my flex shaft and gradually removed the remaining bit under a 5x magnifier (darker spot under the boost port).


After that I hit it with a180 grit scotch brite buff to smooth the area. The screw was completely out and there were no nicks whatsoever but not ideal from a crosshatch perspective.


I didn't want to take any more material off the cylinder but also didn't want to wreck it with a cheap 3 finger hone. A Lisle 15000 would have been nice but that would have been more than 1/2 way to an entire new cylinder. Even though there doesn't seem to be alot of supporters for brush hones and 2-strokes I saw a few applications on youtube where they worked well. The price point was worth a shot so I ordered the 3 1/4" model even though it was listed as too small for the 84mm bore.

The results far exceeded my expectations. Not only did it restore the crosshatch from the minor scuffing it made the embedded screw location almost disappear.



New piston from JM shows up tomorrow so looking forward to seeing if operation cylinder rescue was successful.