Pistons too tight?

[rcb130]

Hello to all,
I am helping a friend do a complete rebuild on a 95 Johnson 150 Hp V6. Here is my question: How tight should the new piston/ring assembly be in the bore? Should we be able to push the piston to the bottom of the bore(with rings installed) with one hand or does it require a rubber mallet to tap it down to the bottom? Piston ring gaps were all inside of the allowable range of .011-023. Pistons without rings could be pushed to bottom of un-oiled cylinders when inserted upside down.
Thanks
rcb130

 

[boobie]

Re: Pistons too tight?

How did you check the piston ring end gaps ??

 

[rcb130]

Re: Pistons too tight?

Hi Boobie,
Put ring into bore, took piston upside down and pushed ring down approx 1 inch. Measured gap with feeler gage. Did this for both rings and on all cylinders with pistons and rings dedicated to a particular cylinder.
Rcb130

 

[phillnjack2]

Re: Pistons too tight?

sounds very strange

sounds like the rings are for over sized pistons or completely the wrong ones.

take a ring off the piston and try placing it in the bore to see if there is a gap !!!!
then measure the actual thickness of the ring compared to original specs.

what make are the pistons and rings ?
has the engine been re-bored ?
if yes did you get the pistons and rings from the engine borers ?


phill

 

[Faztbullet]

Re: Pistons too tight?

If cylinders and pistons/rings are dry it will be tight feeling pushing it up/down bore...make sure cylinder are well oil when installing.

 

[boobie]

Re: Pistons too tight?

You checked the ring gap correctly. As Fazt said, use plently of oil.

 

[dtj]

Re: Pistons too tight?

Ring gap is good per spec..

Is piston diameter to bore diameter per spec.?

If so, you are good to go, lube the piston and bore, and on to the next step...............Don

 

[rcb130]

Re: Pistons too tight?

Phillnjack2,
I did measure ring gaps for all cylinders and gap was within spec.
Pistons and rings are WSM and are .010 over as well as the block bored a tight .010 over standard.
Thanks
rcb130

 

[rcb130]

Re: Pistons too tight?

Don,
Pistons are supposed to have correct diameters for a .010 over size bore. Also to all who are answering or attempting to answer my question. I am doing this in an ambient temperature range of 32-50 degrees not in a heated area of 70 degrees. I imagine the cast iron sleeves would shrink some in diameter but I would expect the pistons to shrink the same or more in diameter. Yes or no?
rcb130

 

[orbanp]

Re: Pistons too tight?

Hi rbc130,

A factory manual should have the clearances listed for the engine. If you do not have it, here are some data for reference, this is from a loopcharged Johnson engine (60HP, 3-cyl) with 3" bore:
Cylinder and piston clearance: 0.0050 max - 0.0035 min
Piston ring gap: 0.017 max - 0.007 min
This should give you some ballpark data.
Cast iron and aluminum have different expansion rates, but the given clearance take this into account. Measuring them at room temperature is fine.

Good luck, Peter

 

[glenn property of pam]

Re: Pistons too tight?

you are using a thin oil for assembly and not a oil addative thats thick in the cold