Engine RPM's

[V6 JOSE]

Yes the mains are in the way, you cant push a piston up through the bottom, but what you CAN do is to push the pistons (sans rods) all the way down the bores (but not so that the rings are no longer in the bores), twist the pistons about 45 degrees to normal orientation, then install the rod and pin from beneath.

This is how my race motor is assembled.

I suppose that is OK, but if you aren't putting floating pins in, you can't press fit the pin while the piston is in the block. As far as I know, the Chev 6 cylinder rods use presed pins, and I don't think there is enough material around the pin bore, to allow machining for floating pins. Am I wrong in my assumptions?

Jose

 

[Jim E]

Think you just answered the why on after market 6 banger rods.... sure they come press or floating.

 

[RootesRacer]

I suppose that is OK, but if you aren't putting floating pins in, you can't press fit the pin while the piston is in the block. As far as I know, the Chev 6 cylinder rods use presed pins, and I don't think there is enough material around the pin bore, to allow machining for floating pins. Am I wrong in my assumptions?

Jose

I use aftermarket (crower) and use teflon buttons instead of finagling ring clips in the pistons pin ends.

Not sure on the stock rods if they were pressed, but the design dims are so close to the V8 rods, I wouldnt think the technology would be any different.

 

[RootesRacer]

Think you just answered the why on after market 6 banger rods.... sure they come press or floating.

You got it, though another compelling reason are 7/16 cap screw fasteners and super light weight (as compared to the rootes rods).

 

[Jim E]

Stock rods are press fit pins.

 

[Tom H]

Ok, I've been trying to follow this thread and am now confused about pins. I am rebuilding my 1725, using Chevy rods (4-6 cyl) and custom pistons. The pins Venolia supplied are (for now) a press fit into both the piston and the rod. The block, pistons and rods are now at the machine shop and the plan is for the shop to hone whichever bore (or both) to achive the proper flex in the piston/rod. The stock Alpine rod has a bronze bushing in it and the pin floats in both the pin and piston. The big question is do I have the machine shop float the pin in both the Chevy (unbushed) rod as well as the piston? Or do I make the pin a press fit in the rod and float in the piston? Or vice -versa? What are the plusses and minuses of each choice? Is there much risk in either? I'm not planning to race the car, but do hope to put a lot of highway miles on it. I have a 3.89 axle and OD.

Thanks,

Tom

 

[jumpinjan]

Does the pistons have circlip grooves? If not, you have no choice but to press fit the rod to the pin.
The pin's fit into the piston is NOT a press fit. It may seem like it, but it you heat up the piston, the pin will loosen.

 

[Tom H]

Jan, Yes, the pistons have retainer clips and grooves. And they deliberately made them "press fit" to give me the option to hone either the rod or piston or both to float.

My shop leans toward press fit in the rod and float in the piston because they are not so comfortable with a steel pin rotating in a steel rod- "like metal on like metal". BUt if I read what you and others have done using the Chevy rods, it seems you had the pins float in both, just like the stock Alpine, even without putting a bushing in the rod.

Or have I missed something?

Thanks, Tom

 

[jumpinjan]

The fit of the pin to the piston, should have been done by the piston manufacturer (Venolia). They have the machines & expertise to do it right. I really question this job done by "shop" personnel.
Just float everything. There's nothing wrong with the steel-on-steel joint. Its getting a supply of oil, the only thing to watch out for is corrosion, but that happens no matter what bearing is used. What is really important is your shop's confidence in getting the correct clearance. I have had parts come from a "shop" in worse condition, then when I brought them in. It happens!
Jan

 

[Tom H]

Thanks, Jan. The shop I am using builds racing engines, so I think they are competent and have the right machines. But I am trying to understand as much as I can myself.

You note that getting oil to the joint is the issue. On the stock alpine, how does oil get to the rod/pin interface? I see there is a hole in the bottom of each piston pin bore - I assume to let some oil splash in there. But there is no similar hole on the small end of the rod. I assume it relies on some splash as well.

Am I right that you floated the pins in both the rod and piston in the Tedder engine?

Tom

 

[jumpinjan]

Yes, the Tedder engine had full-floating pins.
I drilled an oil collection hole at the top of the Chevy rod, just like the Alpine's.

 

[Tom H]

Thanks Jan, I'll do the same. You call it "an oil collection hole". I guess it allows the oil that splashes up to collect in that hole and this allows it to seep into the joint. Had not thought of that. I wondered why the hole on top.

Tom