75hp Starflite Pistons and Rings

[yorab]

So I'm looking at the factory service manual. In the powerhead disassembly section it says,

"When wrist pin is to be removed, LOOSE side of piston must be up and driving tool must be applied to loose side. 'Always drive from loose side to tight side'".

In the reassembly section is says,

"When installing the wristpin, drive from the side marked 'LOOSE', using a fixture to guard against distortion".

This doesn't make sense to me. It seems to me that the pin should go into the loose side and come out the loose side. Am I thinking into this too much?

Also, the manual says not to use an automotive ring compressor when installing pistons into the bores. What do you guys use? What do you use to expand the rings to get them into their grooves?

Thanks.

 

[yorab]

Re: 75hp Starflite Pistons and Rings

By the way, I should note that I want to drive the pins out so that I can reuse the connecting rods. I've bought new pistons, rings, and bearings so I'm not concerned about the old parts.

I'm also thinking of picking up a ball-joint press from Advance auto. Free loaner. With various adapters, I should be able to press out the old pins. Or, if it is better to tap them out, I could do that. If anybody has experience with this, I could use some advice.

I just need to know which way to do this, out the tight side or out the loose side. I found an old post (http://forums.iboats.com/showthread.php?t=344630&highlight=piston+loose) that seemed to indicate that it makes a difference whether you are using a press or tapping the pins out.

Also, should I press the new pins in or should I tap them in?

 

[Dhadley]

Re: 75hp Starflite Pistons and Rings

If you're not concerned about saving the pistons then it doesn't matter. If the new ones still have a tight and a loose side then follow the book carefully. It helps to heat the tight side a little.

 

[yorab]

Re: 75hp Starflite Pistons and Rings

Okay, thanks Dhadley. I'll heat the tight side up a bit before installing the new wrist pins. Any idea if an auto ring compressor would work in a pinch to get the pistons in the bores? Can the rings be opened by hand to install onto the pistons?

 

[Dhadley]

Re: 75hp Starflite Pistons and Rings

The reason they don't want you to use an automotive ring compressor is that it's easy to move the ring(s) and get the ring over the locating pin. They're concerned someone will hit the piston hard enough to break a ring as it goes in the cylinder. Personally I've found it easy enough to tell by looking if the rings are in the groove before pushing the piston in. Plus if someone hits a piston that hard just to get it in a cylinder they deserve to break something. We've installed tens of thousands of pistons and all were with installed using an automotive ring compressor with the correct band (naturally). You can spread the rings by hand if you're careful but we use the standard ring expander.

 

[F_R]

Re: 75hp Starflite Pistons and Rings

The best kind of ring compressor is the factory one, a tapered sleeve. Lacking that, the next best way is just compress them by hand/fingers as they enter the bore. The bore is tapered on the end to make that possible.

Now about that loose side. The book is right. If you press on the tight side to remove it through the loose side, you will distort the piston. For the same reason, it is installed through the loose side, into the SUPPORTED tight side. If you go too far and can't get the snap ring in, you have to go all the way through and start over. Trying to "back it up" will distort the piston.

I've never tried a ball joint press, so can't give an opinion on that. The preferred way is with an arbor press. There is a special tool cradle to support the piston, but you don't need it if you use an arbor press and go the correct direction with the pin.

 

[yorab]

Re: 75hp Starflite Pistons and Rings

Thanks again for the info. One last thing: can I press the new pins in with a ball joint press or should I tap them in? If I had an arbor press, of course I would use that, but I don't have access to one. That's why I could try the ball joint press. I don't have a very good cradle to use to tap the pins in so I'm thinking that pressing may be better to avoid distortion while tapping the pins in.

 

[Dhadley]

Re: 75hp Starflite Pistons and Rings

The pin doesn't press into the wrist pin bearing, it presses into (maybe) one wrist pin boss in the piston. You're going to need a cradle for piston support if the new pistons do indeed have a loose and a tight side. They may be a slip fit on both sides but a cradle is still a good idea.

 

[F_R]

Re: 75hp Starflite Pistons and Rings

Unless they are a recent aftermarket or something, they do have a tight and loose side. It takes more than a "tap". They are a press fit in the tight side. Not having a cradle or press, I suggest it would pay you to take them somewhere for proper assembly. Cheaper than a ruined piston. In the hundreds of motors I've rebuilt, I've never had a cradle. But I did have an arbor press.

 

[yorab]

Re: 75hp Starflite Pistons and Rings

Okay guys, I've just removed the connecting rods. What a bi**h. I found out that a tap is not nearly enough. Even some good whacks with a 5 pound mini-sledge isn't enough. The pins must be pressed out, at least for my motor. It may be different for other motors.

For those who may be interested: the pins press out nicely with a ball-joint press but THE PISTONS WILL BE DESTROYED. So, if you are like me and don't need to reuse the pistons, the ball-joint press will do nicely. If you have an auto parts that has a free loan-a-tool program like Advance Auto, you can't go wrong.

I pressed out the pins both FROM the loose side and TOWARD the loose side just for sh**s and giggles. The pins press out much easier toward the loose side, but as F_R pointed out, the piston skirts can't handle the stress and crack. But if you're not reusing the pistons, who cares. Go the easier route.

I will take your advice F_R and I'll take my parts to the shop so that they can press the pins in with an arbor press. Hope somebody out there can learn from this.

 

[F_R]

Re: 75hp Starflite Pistons and Rings

Be sure your guy understands to get the rods right side up (oil hole). Since it is a V-4, two go one way and two the other way.

 

[yorab]

Re: 75hp Starflite Pistons and Rings

Yep, I even photocopied the pages pertaining to the oil holes in the rods and the directions for pressing in the wrist pins. I'm glad I did as the guy never heard of a loose side and a tight side. Maybe somebody else in the shop knows about the loose side but the particular guy that I talked to didn't. It may have taken a broken piston for them to communicate and figure it out. Also, it finally 'clicked' in my mind as to why the pins must be driven one way only. I now see how the piston is supported by pressing in from the loose side but will be unsupported in the opposite direction.