Mac .21 problems HELP!!

[Keebibear]

I bought a used Mac .21 from a fellow board member here earlier this winter and just today got a chance to run it.I put it in a Seaducer with a 437/3 and AB pipe at 8 1/4 inches and 60% Byrons fuel.Needle was the same start as my previous Mac was in that same hull.First run the boat ran good and got on pipe right away but fell off after 2 laps but still ran pretty good then died.We retrieved it and found the plug bad(which was new),pretty mangled inside the plug.Second run I richened it up 5 clicks and ran good longer fell off and died.**** was it fast.Plug was the same.Third run we went still richer ran really good 4 laps it stalled.It was retrieved and plug was the same again.I was told the pipe might be short so I went from 8 1/4 to 8 1/2. I went to start it and couldnt turn it over with the starter or by hand even with the plug out.It was able to turn with a wrench on the collet but after truning ot over a couple times still will not turn by hand.I dont think it was froze solid but definatly stuck.I had good flow from the water outlet and was not hot to the touch.I could hold my hand on the head after the boat got into the retriev boat.Any ideas?Bearings?Motor was smooth when I got it.Should I go after the seller?Not half a tank and the motors needing new bearings or sleeve/piston.Thanks

 

[warlokboats]

have you pulled it apart to "see" anything wrong? i have had the bottom bushing break apart. check the head clearance?

jon

 

[Don Ferrette]

Sounds to me like you had it waaaay too lean especially when you say it got faster when you fattened it up. Unless you can bring a boat back to shore running, what the head temp is by the time you get to it with the retrieve boat won't tell you much. You said you had good water flow, was this visible while it was running??? I don't think going after the seller is the answer, more like you just got it too hot & cooked it. Tear it down, check it over real good, & check for a piece of trash in your needle. :unsure:

 

[Dan_Cousin]

I'd put money on that its bearings. If they wern't cleaned (you did tear down the motor before you ran it and check didn't you?!?!) they could hve gotten corrosion or pitting and a good hard run is all it took.

I've seen bad bearings take out plugs before.

Seen locked up engines before.

Word of advice. next time an engine locks like that. Take the motor out and tear it down to see what is going on. I cringed when read you turned it over with a wrench. :blink:

You could really turn a small problem into a biger one doing that.

 

[Keebibear]

I used a wrench to turn it over since I couldnt get my fingers around the flywheel and did use little pressure. I have removed it and could turn it by hand with it out BUT after I opened it up the bearings are really smooth and look ok but I cannot move the piston up the sleeve all the way.Maybe half way and I dont want to force it .Is it junk now or a fixable problem?Ive always thought a over heated motor usually loses compression not make it.Yes the water flow was visible on the passes by the dock.

 

[Joe_Knesek]

Any time you burn a plug, the motor is not happy. If the element is missing, it can often be on top of the piston. It's a good idea to take the head button off and look for elements every time you burn a plug.

Unfortunately, it doesn't sound like that's your problem. I think Don hit it on the head. If the motor will not turn over by hand, you have to take it apart to keep from damaging it. Turning it over with a wrench likely damaged it even more than the original failure.

 

[Don Ferrette]

"Ive always thought a over heated motor usually loses compression not make it."

I've seen motors have the sleeve distort from getting repeatedly overheated in back to back runs.

 

[Jerry Wyss]

It's why they always say, "set the needle more than rich before you start",, and put "floatation" in your boat and canopy! :lol: :lol:

 

[Dan_Cousin]

I had a OS 15 that shrunk its sleeve when the engine ran lean and overheated. same symptons your are describing.

I'd take the piston and sleeve out and check the fit outside the engine. The turn the crank over without the rod.

Check the small end of the rod by taking the wrist pin out. Wrist pin ceasure can also case symotoms like yours.

Basically take it all the way apart. Lightly polish the wrist pins, crank and crankpins for the big end of the rod with 0000 steel wool or black scouring pad to remove any discoloration if there are any. Don't get too crazy of you'll change the fit, just knock off the discoloration. If there are heavy wear patterns (grooves) that can't be polished out, pitch it and get a new one.

Before you put it together. Recheck the head clearance and volume. Also take a good look at those bearings. They take a pounding when engine locks like that. Any dimple on any ball, gritty feel (it will be subtle), or discoloration of the balls. get rid of them.

Good luck.