115 inlne 6 question for Clams and other xperts

[daveswaves]

Currently tearing down a 1974 inline 6, cyl 3 rings toast, no compression. All others 130 psi. After removing the crank/assembly there is evidence of overheating/ pre ignition on 3 pistons, 1,3,5 are melted tops and some skirt damage (3 has broken top ring) 2,4 and 6 are perfect, mildly sooted, no scores scrapes rings are free etc. Any thoughts as to why the odd numbered pistons cooked? All the bores look ok and will take a mild hone with the exception of 3 that has a little "transfer" on it. There is no visible evidence of anything "happening" to the motor and the crankcase had the factory seal on the bolt yet so nobody has been in there.

 

[lorax]

Re: 115 inlne 6 question for Clams and other xperts

I had a '73 115 that melted the #3 piston. I was told by a Merc tec that a faulty ignition trigger could cause that. I replaced the trigger and didn't have any problems for five years after I rebuilt it. Then one day I toasted the #3 again.<br /><br />I've always been told not to bog those motors. Make sure it's not overproped.<br /><br />Just my 2 cents

 

[jheron]

Re: 115 inlne 6 question for Clams and other xperts

1,3 and 5 are the top jugs on each carb so they run a little leaner. #3 is a classic melt down on the inlines maybe because the crank has some flex in the middle?<br /> To get rid of the "transfer" use a q-tip and muriatic acid. <br /> Search here for the lync and sync post by Clams, make sure max advance is set no higher than 21, burn mid grade fuel in her and prop it to do 5500 at WOT.<br />Regards Jon

 

[daveswaves]

Re: 115 inlne 6 question for Clams and other xperts

Thanks John, I had forgotten about muriatic acid to disolve aluminum. Good point on the top cyl for each carb, makes sense. I was already planning on 21 degrees as per clams. Got any pistons left from your rebuild? I am 1.5 hours south of you on Longpoint bay I,d be happy to drive up.

 

[jheron]

Re: 115 inlne 6 question for Clams and other xperts

I do have a couple that are salvagable but I would like to hang on to them How many do you need, all 3?<br />If it looks like it got hot I would pull the intake covers and make sure the little plastic restrictors are intact also.<br />Jon

 

[Clams Canino]

Re: 115 inlne 6 question for Clams and other xperts

Too much advance, crappy gas, overpropping. Any combination of the above can be lethal. The odd ones just die 1st is all.<br /><br />-W

 

[daveswaves]

Re: 115 inlne 6 question for Clams and other xperts

Thanks John, Clams, Ill do a rebuild with new pistons, When its on my bass boat it will never be lugged, never be run with crappy gas, never be overpropped, etc. Now, where do I hook that nitrous port

 

[Clams Canino]

Re: 115 inlne 6 question for Clams and other xperts

DON'T USE Wisco!!!! <br /><br />I personally reccomend Persan pistons. Check the Iboats site here to see if they sell them, If not.. get a hold of me. <br /><br />-W

 

[donutter]

Re: 115 inlne 6 question for Clams and other xperts

ive got a 1150 merc u.s model. i have melted one and three pistons twice. would a ignition trigger fix it or is it a fuel problem, please explain what WOT stands for. thank you donutter.

 

[tashasdaddy]

Re: 115 inlne 6 question for Clams and other xperts

wot is wide open throttle, go fast!!!

 

[Clams Canino]

Re: 115 inlne 6 question for Clams and other xperts

Donutter.... any combination of over-propping, too much advance and crappy gas can do this. You gotta set these critters up right to get them to last. And unless you know all is perfect, cruise it at 4000 and save WOT for getting out of the hole only.

-W

 

[donutter]

Re: 115 inlne 6 question for Clams and other xperts

thanks guys. donutter

 

[timmathis]

Re: 115 inlne 6 question for Clams and other xperts

Listen to Clams and make sure it is timed right! TDC also from the start at set up is important. Double check max advance 21 degrees total. I allways check it when it is runing after seting it at cranking speed. If it is set up right and taken care of you should get another good 30 years out of it. They don't build them like that anymore. The new ones are made of plastic and pot metal. They don't want them to last that long anymore.
Tim