Merc 1150 connecting rod question

[monk-monk]

Say you had a set of connecting rods and wasn't sure the rod caps were matched correctly to the rod they came off of, can the cap/rod mating surfaces be milled and the rod crank bore be re-bored/honed back to factory specs?

 

[achris]

Re: Merc 1150 connecting rod question

No.... 2 stroke con rods have the bearing surface hardened to be a bearing surface. Conventional boring is only suitable for white metal type bearing liners.

Depending on the age of the engine, you may be able to rematch the caps with their rods, if you are really careful as they are 'cracked cap' rods. Each rod and it's cap match up perfectly, and the wrong cap will not match.... Worth a try.

Chris...........

 

[monk-monk]

Re: Merc 1150 connecting rod question

Yeah, thats what i thought, seeing how the bearing makes direct contact with the rod surface. So what do you mean by "cracked capped" ?

 

[achris]

Re: Merc 1150 connecting rod question

Automotive engine conrods are made by machine 2 parts, the rod and the cap. 2 stroke engine conrods are made entirely in one piece. Machined, hardened and then the cap is broken off the end of the rod. During the manufacturing process the rod has a couple of weak points machined in, along where they want the cap to break off. That way the cap lines up more accurately and there is less noise and wear from the rod bearing....

Chris......
Did you understand that because I knew what I was talking about and it didn't make a lot of sense to me.

 

[monk-monk]

Re: Merc 1150 connecting rod question

Yeah, i think i see what your saying...if you examine the rod and cap at the parting lines, there should be matching relief marks or casting marks between the rod and cap distinctive to each other? Correct?

 

[achris]

Re: Merc 1150 connecting rod question

Close enough... You may not be able to see them with the naked eye, but if you try to put them together you'll soon tell if you have the right one...

 

[monk-monk]

Re: Merc 1150 connecting rod question

I really appreciate the info! I was just examining these rods with my lighted 4X magnifyer. I do see some marks on the outer bolt bosses that are consistant between rod and cap on a couple of the rods. Im also studying the wear marks on the rods where they contacted the rod in the adjacent cylinder. This is a used set of pistons and rods that i purchased and i just want to be sure the person that disassembled it matched things up correctly.

 

[achris]

Re: Merc 1150 connecting rod question

Are they cracked cap?

 

[monk-monk]

Re: Merc 1150 connecting rod question

I don't think they are...the parting lines between cap and rod are very clean all around the mating surfaces. You know how automotive machinists mark the rods on the outer bolt bosses, a couple of the rods/caps show distinctive marks (like etching) that definitely match. But 3 others sets really don't show nothing. Im going to further examine them for wear patterns at the bearing surfaces.

 

[Faztbullet]

Re: Merc 1150 connecting rod question

The older inline rods are saw cut, machined flat, bolted together and machined to spec's. The older rods are not threaded and use a pass thru pad-bolt/lock-nut to hold in place. These also have molding "dash" and they must line up "dash to dash".

 

[Droll]

Re: Merc 1150 connecting rod question

The new style rods are the "cracked" type....


Arne Kjetil

 

[monk-monk]

Re: Merc 1150 connecting rod question

Thanks for the great info...really appreciate it!! My rods are the older press type bolt. I have a lot of experience with automotive engines, but this is my first with a needle bearing assembly...educate, prepare, and apply...makes things a whole lot easier...Thanks for the little tutorial on connecting rods!