removing rod from a 3 Ring Piston

[dodl]

Hello,<br /><br />As some of you know i try to rebuild my '76 Merc 500 the cheap way. I have 4 used pistons with rods from another engine, and since those pistons are in good shape, i'd like to use them. BUT, the bearing races of the rods are junk. Now i have 4 nice pistons with unusable rods, and i have 3 scored pistons with good rods. <br /><br />The Manual (Seloc) says, i can't reuse a 3 Ring Piston, once i pull the piston pin out. This means, no chance to change the rods??<br /><br />To be honest, i don't see the problem...<br />What's the deal with those 3 ring pistons?<br />Or is it my english and i got something wrong?<br /><br />Here are 2 pictures of the bearing races of the rods after polishing with crocus cloth. They would not last very long i'm afraid <br /><br />

<br /><br />

<br /><br />cu<br />martin

 

[Kenny Bush]

Re: removing rod from a 3 Ring Piston

never heard of that. I have seen a variation in the two ring pistons, in regards to ring thickness. Hopefully someone will chime in for you. I do not see how the # of rings would affect the use of the rod (unless its dimension is different, which I cannot see).

 

[dodl]

Re: removing rod from a 3 Ring Piston

Hi BushCat,<br /><br />It's not the rod. The manual says, you cannot reuse a 3 ring piston, as soon as you disassemble the whole thing. You have to replace the piston and the pin.<br /><br />It just says that without anymore information.<br /><br />I tried it on a scored one and it measures OK. If the statement from the manual is true, i need a whole rebuild kit. And that's too much for my old baby...<br /><br />cu<br />martin

 

[MortenH]

Re: removing rod from a 3 Ring Piston

Hi all<br /><br />In my project - 1984 115HP i6 rebuild - I have planned to replace all bearings and all the piston rings. I am therefore curious to know if this is true - do I have to replace the piston once I have removed the rings and the needle bearings on the wrist pin? I have never read anything about this, and have searched this site without finding any information about this.<br /><br />-M-

 

[Kenny Bush]

Re: removing rod from a 3 Ring Piston

Man I don't know. I have replaced rings on pistons before. I know how expensive it can get doing everything.

 

[dodl]

Re: removing rod from a 3 Ring Piston

Hello,<br /><br />Changing rings is not the problem. But as i understand the manual, you have to use a new piston as soon as you remove the wrist pin on a 3 ring piston.<br />I too hope, that i got something wrong here...<br /><br />cu<br />martin

 

[rodbolt]

Re: removing rod from a 3 Ring Piston

what manual is that? I have never heard of the throw away piston so I may get a chance to learn today. the piston circlips are throwaway one use items but I never heard of one use pistons. I have heard of pistons being destroyed cause the pins were pressed in or out from the wrong side.<br /> post the paragraph with the piston statement.

 

[dodl]

Re: removing rod from a 3 Ring Piston

Sorry rodbolt,<br /><br />I gave the manual to a friend and will get it next week. But yes, i will post the paragraph as soon as i get it. It's the Seloc Manual http://www.selocmarine.com/cart/product_detail.cfm?item__code=1406 and the paragraph is at "inspecting and cleaning" in the powerhead section. <br /><br />Is there a wrong side to press out the pin?? I pressed out the pins of the damaged pistons, and they seemed to come out in both directions with similar force applied.<br /><br />thank you<br />martin

 

[rodbolt]

Re: removing rod from a 3 Ring Piston

without consulting the factory manual all I will say is on the mercs I dont recall any particular direction of press just the reccomendation to heat with a heat gun for 60-90 seconds to aid pin removal and insertion.<br /> OMC did make some pistons that pin removal and insertion was from one side only. pistons had an L embossed on the loose side. I dont think I own that seloc but I may have a factory manual about someplace.<br /> but when you get your manual back I would like to read that paragraph.

 

[MortenH]

Re: removing rod from a 3 Ring Piston

I just read the entire "inspecting and cleaning" section of my Seloc, without finding any recomandation of replacing pistons, just a general advice to replace the wrist pin bearings. My manual covers 90 to 250 HP V6 and I6 engines, but I have seen that the pistons fram a 50 HP engine can be used in my 115 HP (or rather in the 90 HP i6?), so I guess this would apply on my project too.<br /><br />-M-

 

[dodl]

Re: removing rod from a 3 Ring Piston

Norway, i would be VERY happy, if i understood something wrong, or if the statement in my seloc is wrong. I currently have 4 Pistons lying on my kitchen table which i'd like to use.<br /><br />I hope to get my seloc monday or tuesday. Then i will post the paragraph. What i found out with my pistons, the pin came out not too easy. But now it goes in pretty easy, and i can rotate it with my finger once inside again. Don't know if this is good...<br /><br />cu<br />martin

 

[MortenH]

Re: removing rod from a 3 Ring Piston

Dodl - drop me a mail, so we can discuss this, and post the result: morten@dalehareide.net<br /><br />-M-

 

[Droll]

Re: removing rod from a 3 Ring Piston

Got the maual from Clymer ,did not find any notes about removing rods from INLINE pistons BUT found it on the early 3-ring V6 pistons .

CAUTION : Early V6 engines use a 3-ring piston that cannot be reused if removed from the connecting rod.<br />Unless the the piston, piston pin or connecting rod must be replaced .

They did not say why .

 

[dodl]

Re: removing rod from a 3 Ring Piston

Hello,<br /><br />Well, i found out, there were a lot of different pistons between 1969-1973. Don't know if the "no reuse" pistons are all 3 rings, or only the older ones.<br /><br />Norway, i'll send you a mail after work. <br /><br />thanks<br />martin

 

[dodl]

Re: removing rod from a 3 Ring Piston

Hello,<br /><br />@rodbolt, i got the paragraph from the manual now.<br /><br />It says: Piston service<br /><br />Critical words<br /><br />Never attempt to reuse a 3-ring piston once it has been removed from a connecting rod. When the piston is removed, from the rod, the piston is damaged and unfit for further service.<br /> <br /><br />Doesn't sound too good to me. To be honest, since i am on a really tight budget, i will try the used ones though...<br /><br />cu<br />martin

 

[dodl]

Re: removing rod from a 3 Ring Piston

Hello,<br /><br />OK, i got some responses at "John's old mercury board".<br /><br />They say "go ahead and use them", or "it's the seloc, that shouldn't be reused" <br /><br />Now that's what i wanted to hear <br /><br />cu<br />martin

 

[MortenH]

Re: removing rod from a 3 Ring Piston

Sounds great. Now I can reuse my 3 ring pistons without worry. Great!<br /><br />-M-

 

[Clams Canino]

Re: removing rod from a 3 Ring Piston

Agreed......... also it helps to get the pin in and out if you warm the pistons a bit.<br /><br />-W

 

[dodl]

Re: removing rod from a 3 Ring Piston

Hello,<br /><br />Well, so i wanted to reuse those pistons. Now my daughter built a nice tower - with my wrist pins...<br /><br />As far as i know, the pistons and pins are matched. I don't have a clue now, which pin was at which piston.<br />They all go in pretty easy. I can push them in with my thumb. I even wonder if they are too loose?? Now, are they really matched that exactly and is this critical, or can i just push them in and run it?<br /><br />thanks<br />martin

 

[emckelvy]

Re: removing rod from a 3 Ring Piston

Can't tell you how many motors I've rebuilt in the past and have swapped/changed many a rod/piston assy where the only thing done was replace the wrist pin bearings and wrist pin circlips. Never have I experienced a failure due to swapping out.<br /><br />And although they don't recommend swapping wrist pins I've done that on rare occasion without ill consequences.<br /><br />If you have access to a micrometer you might try measuring the various wrist pins to see if there's any difference dimensionally. I don't expect you'll see any significant difference.<br /><br />I've also seen some pistons that didn't have a real 'snug' fit with the wrist pin and that didn't seem to make a lot of diff either. After all, the hot-rodders run 'free floating' wristpins all the time. Not a direct comparison but it is done.<br /><br />OMC pistons typically have a real tight fit and you have to 'boil' them in water then use a press with special fixture or you'll break a piston. Most of the Mercs are a lot more forgiving than that.<br /><br />Back when I started working on Mercs, I did tons of the old 100HP inlines. Swapped pistons & rods right and left. I didn't know any better and didn't have a torque wrench for the rod bolts either. Just torqued by 'feel' and used a bit of red Loctite. They always ran fine! Later found out my 'torque by feel' was around 180 inch-lbs, fancy that!!!! lol.<br /><br />HTH and Good Luck with your engine build.