i cant get the pistons back in the bores

[fishingman220]

i am rebuilding my 350 merc and i have the bores honed and the new rings on the pistons, i cleaned the grooves on the pistons and made sure i have the right rings. i put just a ring in the bore and i have .022 gap. but i have tried 2 different ring compressors and it is still not going into the bore. what could i be doing wrong

 

[mla2ofus]

Re: i cant get the pistons back in the bores

Do you have lots of oil on the piston and rings, also plenty of oil on the overlapping part of ring squeezer?
Mike

 

[fishingman220]

Re: i cant get the pistons back in the bores

no, maybe i should try that

 

[fishingman220]

Re: i cant get the pistons back in the bores

i got one half way in and then took back out, and i seemed so tight that if i got all eight in i wouldnt be able to spin the crank. would it loosen up once it got all the way into the bore?

 

[ENSIGN]

Re: i cant get the pistons back in the bores

Do you have the piston rings on in the right direction? there is a dot on the ring which points up.make em slipery,lots of oil in cylinders and on pistons!!!

 

[bigskiohio]

Re: i cant get the pistons back in the bores

been awhile but you tap them in with the wooden handle of a hammer they will be snug but not super tight.

 

[Fishermark]

Re: i cant get the pistons back in the bores

Well, if you are using the same pistons, you can at least eliminate them as a source of the problem. It also sounds like you checked the gap of all the rings... so that leaves the install method you are using.

What type of ring compressor are you using? The type that tightens around the piston assembly or the tapered style? I usually have a coffee can full of clean oil that I dip the entire piston assembly into and then use the proper tool to install the piston into the bore. I use the handle of a mallet to tap the assembly into the bore. If it doesn't go smoothly, then the chances are good that the ring is getting caught - slipping out of the tool before it enters the bore.

Check to make sure you have the right sized tool and be sure it sits down completely on top of the bore.

Are you sure you cleaned the grooves well? Nothing keeping the rings from settling down completely in the piston?

 

[fishingman220]

Re: i cant get the pistons back in the bores

the tool i am using is a snap on ring compressor with a tapered band and a specal set of lock pliers that compress the rings, i am tapping on the piston with a mallet handle and they are super tight. i cleaned the pistons in a parts cleaner with a brass brush and used a broke piece of ring to clean the groves. i think like you said that it is slipping out of the piston right before it gets into the bore.

 

[dr_bowtie]

Re: i cant get the pistons back in the bores

I lightly oil the bore itself....

When you use the ring compressor tool make sure it is sitting squarely against the block...if it isnt and you dont notice the ring will pop out before it goes in the hole...and if you push it you'll end up with a broken ring and a hole that uses lots of oil...

I have an adjustable I use that I got at Ridge Auto parts and I have been using that same one 25+ years..but some day I am going to switch to the taper bore piston installers...

good luck

 

[fishingman220]

Re: i cant get the pistons back in the bores

thank you, i will try some oil i will work on it later and get some pictures if i cant get it back together. how long will break in take? i am using cast rings

 

[dr_bowtie]

Re: i cant get the pistons back in the bores

well what I do is run it to set the rings....if it has a flat tappet cam I will run it from 2,000rpm-3,500rpm and oscillate it...this does several things...1) lubes the cam...only thing that lubes the cam is splash...(what get thrown off the crankshaft)
2) it builds heat int he cylinders...you want the rings to get hot to seat them...I am not saying over heat the engine but I have had a few get up over 200degs in a closed loop...

I am honestly NOT sure how hot a engine would get in a boat with muffs or in the water so you may want to read up on that...

I will run one for 25minutes give or take than I will shut it down and let it Completely cool before it is refired...the heating/cooling process is what sets the rings...

I have never had an issue with rings not setting this way...

 

[fishingman220]

Re: i cant get the pistons back in the bores

after it cools, how much longer is the break in time before you can run it like nomal?

 

[rodbolt]

Re: i cant get the pistons back in the bores

look carefully at the tool. it MUST be oriented with the arrow up or it wont work.
same set I have by blue point and it works very well.

 

[fishingman220]

Re: i cant get the pistons back in the bores

mine says botom with an arrow pointing down, and says i think 3 3/4 to 4 1/8

 

[dr_bowtie]

Re: i cant get the pistons back in the bores

after it cools, how much longer is the break in time before you can run it like nomal?

after it cool break it in like you want it to run...! just watch teh temps...thats all..I have never blown an engine...ever

 

[fishingman220]

Re: i cant get the pistons back in the bores

ok cool, thanks

 

[Z71Man]

Re: i cant get the pistons back in the bores

I had a similar problem to this one rebuilding a 350. The new rings would go in with no piston, but with the rings on the piston there was no way to get the assembly into the bore. Turned out that the parts store had given us rings for a Ford 351 in spite of assuring us that they were for a 350. With the right rings it went together just how it should have!

You might double or triple check your ring part #'s.

 

[JustJason]

Re: i cant get the pistons back in the bores

May actually want to get a mic and a cylinder bore gauge and map it out to make sure the machinist did his job correctly. You need a Micrometer to fit the pistons and to double check your piston to cylinder wall clearence too.

 

[dr_bowtie]

Re: i cant get the pistons back in the bores

except he is using the same pistons and new rings...the pistons should fit with no issue...the only "variable" is the rings...

 

[sockos]

Re: i cant get the pistons back in the bores

I would recheck your oil ring set up.
Also was there a lot of cylinder ridge on the engine?
Ridge won't effect assembly but may have effect on top ring later on.