Question Can 15 oversized rings be used on a standard piston? 70 Merc

[Maxz695]

I have cleaned and soaked the ring grooves and rings then reassembled and soaked the pistons in Premix before rinserting them into the cylinders. I have good pressure in those two cylinders with the spark plugs hand tight but not quite as much on the third cylinder. I have lightly honed the cylinders. I have a 115 piston on the way. It,s the same as the 70HP. My queston is would I have to get the oversized piston to use the .15 oversized rings or could I use the .15 over on the standard piston?

 

[Chinewalker]

Re: Question Can 15 oversized rings be used on a standard piston? 70 Merc

Racers do it all the time. Be sure to file the ends down to get proper ring end gap.

 

[Maxz695]

Re: Question Can 15 oversized rings be used on a standard piston? 70 Merc

Thank you very much for the info and the quick reply

 

[Faztbullet]

Re: Question Can 15 oversized rings be used on a standard piston? 70 Merc

could I use the .15 over on the standard piston?

I have never seen this successfully done on a Merc piston...if the cylinder is that worn it needs to be bored.

 

[Maxz695]

Re: Question Can 15 oversized rings be used on a standard piston? 70 Merc

This cilynder had good compression 140 psi when I took it down. The cylinder with the bad piston now has good pressure with very little blow by with one if the other pistons inserted. I,m waitng for my other piston to show tomarrow and will make sure it is well drenched in premix when inserting it. Like I said I busted the glaze lightly. My question was would a .15 ring work on a standard piston. If I over honed it slightly. It would make sense that .15 thousandths of an inch would already have been bored off the cylinder. It would also make sense to check the gap for the ring lock and adjust accordingly by filing it. The thing I wanted to know is can I use a standard piston withy the oversized ring or do I have to aquire an oversized piston. Testing compression at this stage is imposible as the motor is completely dismantled. I,m aware of what kind of pressure is acceptable. Even the bad piston held 120 compression and this is no worse than that one was.

 

[Dukedog]

Re: Question Can 15 oversized rings be used on a standard piston? 70 Merc

could I use the .15 over on the standard piston?

Only if your gonna sell it to your brother-in-law............who lives on tha opposite coast.

 

[Maxz695]

Re: Question Can 15 oversized rings be used on a standard piston? 70 Merc

LOL well being on a fixed income of less than 700 a month and besides I am gonna try the stock piston and rings when they show tommarrow. with the crank and stator If the piston feels as good as the rest it,s put it together time If Not It,s oversized piston and rings. This is not a boat i,m gonna ride out into the middle of the gulf of mexico. Just around the inland waterway within 7 miles Hell I could row to shore or even walk and then hitch home lol View attachment 169776View attachment 169774View attachment 169773 So I have 1 admiral saying yes and 1 admiral saying no. Then I have dukedog Hmmmm I hope i,m not the one confused here. I,m gonna keep everyone updated and I,m seriously considering having it check to bore .30 over with new pistons rings pins needle bearings wrist and connecting rods over the winter if things don,t look good tommorrow. Processed through USPS Sort Facility
1982 MERCURY 70HP CRANKSHAFT ASSEMBLY
Sep-25-12, 20:14 PM, TAMPA, FL 33605

Depart USPS Sort Facility

Sep-25-12, 00:00 AM, JACKSONVILLE, FL 32099

Processed at USPS Origin Sort Facility

Sep-24-12, 21:54 PM, JACKSONVILLE, FL 32099

Accepted at USPS Origin Sort Facility

Sep-24-12, 20:39 PM, JACKSONVILLE, FL 32205

 

[Dukedog]

Re: Question Can 15 oversized rings be used on a standard piston? 70 Merc

I'm one of those racers but retired (quite a few years now). Myself and everyone I know would not even consider doin' that unless it was a last resort and had to in order ta make another round with no reguard ta what happens to tha motor. But I will add, this is only on tha v6 merc/mariner. On tha inline ya might get away with it. Donno?..............jmo

Tha problem with tha makin' tha end gap right is the amount of material thats gotta come off ta make it fit. Whether it be Keyston or Rectangular end it still has ta fit tha pin. You lose tha tolerance around tha locating pin in tha piston so tha ring will not close as it should plus it changes tha ring "tension"...............

 

[Maxz695]

Re: Question Can 15 oversized rings be used on a standard piston? 70 Merc

Thanks for the input. Anotherwords Unless I,m going for a last hellride I should if the standard piston doesn,t fly tonight in the pressure test, to bore it out and get the oversized piston with the rings and cannot use the .15 over on a standard piston with any gaurantee. Thanks Thats what I asked in my question

 

[Dukedog]

Re: Question Can 15 oversized rings be used on a standard piston? 70 Merc

New standard piston and rings, even with lower compression, would run longer (imo) than what tha other way would............GL

 

[Maxz695]

Re: Question Can 15 oversized rings be used on a standard piston? 70 Merc

I believe you It may be ok. Like I said I have to check the piston coming tonight. I don,t beleive I over honed the cylinder as the bad one i honed works nicely now. I may not have lubed the cylinder enough when I put the piston in it and worked it after cleaning it with carb spray to remove all particals from the walls and drain out the spark plug holes.

 

[Maxz695]

Re: Question Can 15 oversized rings be used on a standard piston? 70 Merc

The piston showed today along with the stator and the crank The piston appears to be the best of them all after soaking in premix and inserting it. Great presure in and out. Bad thing is The Crank is froma 1982 mine is a 1979 both 70 HP I made a new post about this issue. If I line up #1 Journal on them both the #2 journal is in the #3 position and the #3 journal is in the #2 position. See new post as not to confuse the two posts. It,s about a coil swap from the switchbox to the cylinders to accomidate the new crank

 

[wired247]

Re: Question Can 15 oversized rings be used on a standard piston? 70 Merc

As an old-ish drag racer who has built hundreds of engines for myself and commercially I would never try using a .015" over ring on a standard bore. File to fit rings are just a few thou over. Not 15 thou and that ring will have a completely different set in the bore and will wear the cylinder prematurely. Bad idea.

 

[Maxz695]

Re: Question Can 15 oversized rings be used on a standard piston? 70 Merc

that idea has been trashed the standard piston and rings came today with good results. What about my crank issue though. The guy I bought it from said it can be done. Did Mercury molsd a new crank so that unknowing people couldn,t use older switchboxes on the newer engines to sell more parts? firing order would be 132 instead of 123 thats the only difference