Floating Pins how to?

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bschubarg

bschubarg

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I am building a some what of an unusual stroker 318 and have a quick question with some more soon to follow since this is going to be my first engine build and leave it to me to make it a stroker.

Anyways, I have a set of 340 Rods that are bushed. I also have a set of pistons that are for either pressed pins or floating. The O ring gap is present on both ends of the wrist pin openings on the piston.

The pistons came with pressed pins but I want floaters. Is there machining involved to get the pins to float or do I purchase pins made to float?

What do I need to do to get this assembly to be a full floating rod piston assembly?

BTW, the block is a 318 with a Forged Stroker 3.51" to make my bored 0.030 a 341 CU. IN. It will also have Magnum heads and a Air Gap intake with a yet to be determined carb(leaning towards a Rochester Q-Jet). Most of the parts damn near fell into my lap(read cheap) so I don't want ot hear...."Why not just build a 360....?"

I plan on taking pics as soon as I get all the pieces together(bearings, machining, etc) before I assemble. I am hoping some of you guys can walk me thru this. Now just exactly, what is a torque wrench....? J/K
 
I cant help ya with the tech but keep us informed. Are you gonna dyno it when youre done? It would be really interesting in what that makes when youre done. good luck.
 
If the 340 rods are bushed already then it's just a matter of makeing sure that the bushings are in spec and your done. As the pins should just slide into the rod and then the locks are installed. The pins have to be the size that they are as they fit the piston and you make the rods fit the pin if any machining is needed to be done.
 
the pistons should have grooves on the outside end of the pin hole for locks, I like the spiral locks even though they are a pain to install. You can buy the locks seperate from Hughes engine, etc.
 
a torque wrench is what you will need to assemble an engine, as every bolt has to be torqued. Torqueing means to tighten a bolt to a certain specification. Almost all engine manuals or hotrodding book will have a page with all the torque specs for all the bolts on that particular engine. Torque is usually in ft.lbs.. This is the amount it takes to stretch the bolt a certain amount. There are different style torque wrenches, but the most common nowadays is the "clicker" style. You rotate the handle to what ever amount of ft.lbs. you need. Then you tighten the bolt until you hear the click, which indicates you have reached the figure you dialed in on the handle. You can buy at a parts store or can usually rent a a rental store. You will need one that goes from 10 ft.lbs. to 150 ft.lbs. Can buy a cheap one for around $60.00 or a better one will run about $125.00. Hope this helps. Hope I explained it well enough.
 
My engine guy said for a street motor that will not be torn apart every season press pins are the best. Seems like those locks get loose, well maybe even one could cause problems and you have 16 to worry about. He also said you really don't need it till around 7000 rpms.
 
I agree with dodge freak on the need for floaters as I have had some locks come loose before but I wouldn't go out of my way to dump them to go for the pressed fit either ...use what you have either way
 
All factory 340s and many 318s used floating pins...I have seen a couple factory locks fail, but it's rare. Much more common for a set of locks to not be installed fully or properly, and then things come apart...Floating pins can put up with more load and abuse..in addition to being able to be taken apart easy..
 
Being I spend 25 years of my past life in rental stores I would not rent a click style torque wrench ever! only rent a dial type. When I had the click style they were always being returned all turned up, I am also sure they were used as breaker bars and lord know what else. We use to get them re-certified and the report that came back showed that they were out as much a 15 ft lbs sometimes. Then the re-certing started to cost more that the rental so we got rid of them. I would invest in a good torque wrench of your own. If you are going to build one motor you will probably build another. If you take care of it it will last you for ever. Also like a paint gun don't ever lend it out for the reasons I stated earlier. If a buddy needs something torqued go over and do the torqueing for them. There are certain parts of a motor that if not torqued correctly can cause some serious uglyness.
 
B-Mod Dad said:
a torque wrench is what you will need to assemble an engine, as every bolt has to be torqued. Torqueing means to tighten a bolt to a certain specification. Almost all engine manuals or hotrodding book will have a page with all the torque specs for all the bolts on that particular engine. Torque is usually in ft.lbs.. This is the amount it takes to stretch the bolt a certain amount. There are different style torque wrenches, but the most common nowadays is the "clicker" style. You rotate the handle to what ever amount of ft.lbs. you need. Then you tighten the bolt until you hear the click, which indicates you have reached the figure you dialed in on the handle. You can buy at a parts store or can usually rent a a rental store. You will need one that goes from 10 ft.lbs. to 150 ft.lbs. Can buy a cheap one for around $60.00 or a better one will run about $125.00. Hope this helps. Hope I explained it well enough.
Click to expand...

You made my day. I was waiting for the punchline and when there wasn't any, you had me floored in laughter!!! I was j/k about the t/q wrench. I have a couple, one for ft /lbs and one for inch/ lbs.

My sense of humour doesn't come thru very well in these forums. But you did make my day.. thanks...

And yes, you did a great job describing what a t/q is and what it does...
 
So Moper... tell me, why is it very difficult to press in the pin thru the piston. I was under the impression that all that is needed to assemble the rod/piston assembly with full floaters is just a bit of elbow grease ans some spiro locks. The engine will night even come close to the 7000 rpm, more like 5500 max.

Just simply, I did all of the polishing on a set of 340 rods and would hate to give up all that work if I need new pins and pistons...
 
"Pressed pin" refers to the pin and small end of the rod. It has nothing to do with the piston to pin interaction. That's why you have pistons that can go either way. With full floating, the pin can float in the small end, in a bronze bushing. And the lateral (sideways) movement is stopped by clips that go in the grooves you see machined in the ends of the pistons' pin bores. With pressed pins, the small end of the rod has no bushing, and it gets heated in a rod heater to expand the pin bore. While it's hot, and the pin is room temp, the rod is pulled from the heater, slipped in the piston, and the pin is slipped thru the piston and rod. In a matter of a second, the pin cools the rod, and it shrinks to normal size, locking the pin in place. A seasoned guy makes it look like nothing. I've never done it successfully..lol. They never end up centered the way they should be. I pay the shop to do it. But that means the pin is retained by the press fit, so there will be no clips used in the groove in the pin bores, or no grooves present at all.
 
Careful on heating, have seen lots of engines come apart from bad rods. Lots of tricks to lots of things.
 
hi, the pins in your pistons will fit either float or pressed rods. the rod bores are the same inside diameter. the press style will be somewhat smaller in relationship to a floater. just make sure there is the correct clearence in rod bore. the pins will slip right in, install locks. A floater pin setup is the best way to go. pressed are a pain in the rear. your rods have bushings in them already, so floated is only way you can go.
 
Ive done hundreds of press pin installs...had a machine made to do it with a stop on it so all 8 would come out the same and in the right spot...and a special fixture for removing them in a press

the max heat for the con rod is 450F

make sure if you use stock type C clips on your floaters you orient them the correct way or they can come out
 
'C' clips should be installed with the 'gap' at the 12:00 position. Never at the 9:00 or 3:00 position. Inertia can cause the clip to compress enough to fall out of thier groves. Have seen some installed at the 6:00 position, but I wouldn't install them there. Floating pins are the way to go. Good luck, Terry.
 
Thanks again for the info. I was going to attempt the "moper" method, but I think I'll just let a competent machinist do it for me.
 
The "moper" method? That's how a shop does them. My metohd is, I pay my machinist to do them. The rod heater is part of every shops equipment list. And in my case, the guy knows to keep them "just warm enough". He's been assembling professionalil for over 20 years now. If the rod's pin bore discolors, it's too hot. I've seen some really blue examples..that's way too hot IMO.
 
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