3.0 replacement piston?

[fngboater]

so i went to check out my block at the machine shop to see how the new sleeve looked and it looks nice.
i am only needing to replace the one piston in that sleeved cylinder. its supposedly a replacementfor the original but the skirts on the piston are longer and its got the teflon? coating on it. will that be ok to replace the original and be different from the other 3? should i balance it to match the weight of the others? sorry i didnt think of taking any pictures of the "replacement" piston while i was there.

 

[Bt Doctur]

Re: 3.0 replacement piston?

rotating assemblies should be balanced to each other to keep the vibration to a minimum

 

[Bondo]

Re: 3.0 replacement piston?

so i went to check out my block at the machine shop to see how the new sleeve looked and it looks nice.
i am only needing to replace the one piston in that sleeved cylinder. its supposedly a replacementfor the original but the skirts on the piston are longer and its got the teflon? coating on it. will that be ok to replace the original and be different from the other 3? should i balance it to match the weight of the others? sorry i didnt think of taking any pictures of the "replacement" piston while i was there.

Ayuh,... Is yer Machinest aware of this,..?? What'd he say,..??

 

[fngboater]

Re: 3.0 replacement piston?

Ayuh,... Is yer Machinest aware of this,..?? What'd he say,..??

yes he is aware of this and made sure to show me. he told me that it shouldnt be a problem. (probably stupid of me to second guess a reputible engine builder huh) Ill probably go with it but ill make sure to balance it as close as i can to the others. thing is i am trying to save money so ill be reassembling the motor myself. i might as well do some static balancing and mild polish the head while waiting for the rest of the parts to come. i am thinking the best place to remove weight from the piston is on the underside of the crown...is this correct?

 

[franktrav]

Re: 3.0 replacement piston?

when weight matching pistons.... "material removal" machining is done either under the piston pin boss with a special offset cutter, or it is done by drilling holes (very carefully) on the surface of the pin boss. You do this to both piston bosses, sharing the material loss. You DO NOT want to remove the material off only one side
goodluck

 

[fngboater]

Re: 3.0 replacement piston?

well i finally got the weight of the pistons and the old one is 612.35 grams and the new one is 635 grams which is a difference of 22.65 grams. can you take that much out of a piston? it is a replacement from engine tech.

 

[Don S]

Re: 3.0 replacement piston?

You need to get the correct piston from Mercruiser if it was an OEM engine and not some after market rebuild.

Go by engine serial number, not by the year of your boat.

 

[fngboater]

Re: 3.0 replacement piston?

You need to get the correct piston from Mercruiser if it was an OEM engine and not some after market rebuild.

Go by engine serial number, not by the year of your boat.

i guess ill try that and try to return the piston that i got. yeah the engine is all original never been rebuilt, standard everything . i did get new rings and new main, rod, and cam bearings and new brass freeze plugs. just waiting for the piston now to call it a short block

 

[fngboater]

Re: 3.0 replacement piston?

ive tried to look up the part number on the piston and cant find it. number on the piston is 14096629. the block s/n is f88371. can someone tell me where i can find a factory replacement standard piston for this thing.

 

[Don S]

Re: 3.0 replacement piston?

the block s/n is f88371

It's one number short.

 

[fngboater]

Re: 3.0 replacement piston?

It's one number short.

sorry bout that its f881371

 

[Don S]

Re: 3.0 replacement piston?

This is one option, google the part number. DO NOT get an aftermarket, or you will be in the same predicament you are now.

http://www.marineengine.com/newparts/part_details.php?pnum=MER733-810852&ptype=&Engine=&Model=

 

[fngboater]

Re: 3.0 replacement piston?

yeah those look the same as my originals. i think ill call them to see how much they weigh. i wish they were cheaper though. i did try to google the piston p/n and came up with nothing. as far as the replacement that i do have, which is 23 grams heavier, are we in agreeance that that is too much of a difference to run how it is

 

[fishrdan]

Re: 3.0 replacement piston?

23 grams is LOT, .8 ounces or 5% of a pound.

When I rebuilt my engine I didn't balance it, but weight matched everything, better than nothing... (From all the grinding marks on the crank and rods, it looks like it was factory balanced.) 3 of the pistons were close, within a few grams, but one piston/pin was way out, something like the difference you have. I asked the machinist and he said to take a majority of the weight off the piston pin as it would be removing too much from the piston. This was a set of pistons, no idea why 1 of them was so far off, but it was.

 

[fngboater]

Re: 3.0 replacement piston?

you say you took the weight out of the pin? i know out of the inside but where? maybe that ridge in the center of the pin? have any instructables?

 

[fishrdan]

Re: 3.0 replacement piston?

Right off the end of the piston pin, something like 1/4", with a vertical belt sander. Put some tape around the end of the pin and start sanding it, keep it cool with ice while removing material.

Ask your machinist if this is right for your situation.