Powerhouse Posted February 19, 2013 Report Share Posted February 19, 2013 Anyone know the oil clearance specs for a new wrist pin bushing? I know the stock pin should be from .8591 to .8593 in diameter. Can the clearance be figured out that way? I want to make sure the machine shop I use does it correctly. I am not sure the last guy did. Thanks all. Quote Link to comment Share on other sites More sharing options...
randroid Posted February 19, 2013 Report Share Posted February 19, 2013 Powerhouse, A straight answer is that no, I don't know the clearance, but I do have some information that might confuse the situation and that's when I'm happiest so here goes: It is generally accepted that an oil film is .0005 thick, which is half a thousandth if I got my decimal places right. Since that film is on both sides of the piece it totals .001. The clearance for heat expansion is generally .002, which give a total clearance of .003. Any more than that is too loose so logically any less is too tight, but these are figures to keep in the back of your head only to be used if the machinist says something like, "It's good enough". Hope somebody else can be more specific. -Randy Quote Link to comment Share on other sites More sharing options...
Joe Flanagan Posted February 19, 2013 Report Share Posted February 19, 2013 That figure is probably in your manual, if you've got one. Check under "specifications" at the beginning of the engine section. Quote Link to comment Share on other sites More sharing options...
Dave72dt Posted February 19, 2013 Report Share Posted February 19, 2013 The truck repair manual says wrist pins should require a tight thumb pressure to install when all parts at normal room temp.. Quote Link to comment Share on other sites More sharing options...
Joe Flanagan Posted February 19, 2013 Report Share Posted February 19, 2013 (edited) Yep, that's what my car manual says. The specs they give are .0000 to .0005. Edited February 19, 2013 by Joe Flanagan Quote Link to comment Share on other sites More sharing options...
mayflower48 Posted February 19, 2013 Report Share Posted February 19, 2013 I just did my rods. I have a Sunnen honing machine to do them on. They (Sunnen) call for .0003 to .0005 for a full floating pin of this size. You can not have .0000 clearance, it will be a press fit. Any good automotive machine shop will have this type of machine. Quote Link to comment Share on other sites More sharing options...
Dodgeb4ya Posted February 19, 2013 Report Share Posted February 19, 2013 More of the rod bushing press fit info out of the special Dodge Truck service bulletin dated 1951. Quote Link to comment Share on other sites More sharing options...
Powerhouse Posted February 19, 2013 Author Report Share Posted February 19, 2013 (edited) Thanks much all. Thumb press fit is mostly what I can find. I also read 55/64(.859375) bushing I.D. and the pin diameter should be .8591-.8593 So for pin clearance in rod eye bushing: .8593(larger spec given for a pin) + .0005(clearance)= .8598 But if the bushing ID is to be .859375 than that makes for no clearance. Is that right? I am no math guy. Is that not the same for the pin in piston clearance...or is that what they call the thumb press fit at room temp(70°)??? I tested my worn pins in my old pistons and they had to pretty much be hammered in. Randroid, I am a bit more confused now...but that's better than being stuck in neutral. hahaha Edited February 19, 2013 by Powerhouse Quote Link to comment Share on other sites More sharing options...
Powerhouse Posted February 19, 2013 Author Report Share Posted February 19, 2013 (edited) SO...since I am getting really confused...are the pins supposed to be tight in the bushing and move around in the piston? OR are they supposed to be tight in the piston and move around in the bushing? Which one is the solid fit? Or are they both supposed to move? Edited February 19, 2013 by Powerhouse Quote Link to comment Share on other sites More sharing options...
Plymouthy Adams Posted February 19, 2013 Report Share Posted February 19, 2013 per the book there are two test of the wrist pin..one, fitting to the rod only and another fitting to the piston boss less rod..if these pass the test..it is 'assmued' that the combination of the three items a matching combination suitable for assembly and use in the engine.. Quote Link to comment Share on other sites More sharing options...
Powerhouse Posted February 19, 2013 Author Report Share Posted February 19, 2013 Thanks. I am guessing they both move then? I'll have to check the book later. Any pointers till then are appreciated. Quote Link to comment Share on other sites More sharing options...
Plymouthy Adams Posted February 19, 2013 Report Share Posted February 19, 2013 yes..these are not interference fit...thus the retainers within the machined area of the piston bosses Quote Link to comment Share on other sites More sharing options...
Powerhouse Posted February 19, 2013 Author Report Share Posted February 19, 2013 so I guess that's what floating pin means. I noticed a bit of wear on the retaining clips due to the pins becoming too loose and banging on the clips. Quote Link to comment Share on other sites More sharing options...
Powerhouse Posted February 23, 2013 Author Report Share Posted February 23, 2013 has anyone evr had to hone piston to fit the wrist pins? I have a set of elco pistons and pins but the pins are too tight to press in with my thumbs. I actually had to tap the thing back out with a mallet and it was only in a bout 1/4 inch. Quote Link to comment Share on other sites More sharing options...
mayflower48 Posted February 23, 2013 Report Share Posted February 23, 2013 If the pistons are used there might be a small burr at the snap ring groove. This is common with round snap rings. If they are new pistons that has new pins and the air tempature is cold try putting the pistons in hot water for a few minutes. If that does not work, then you will have to have a machine shop lightly hone the piston to .0003 to.0005 clearance. Quote Link to comment Share on other sites More sharing options...
Powerhouse Posted February 27, 2013 Author Report Share Posted February 27, 2013 Thanks all. I will let ya know how it worked out. Quote Link to comment Share on other sites More sharing options...
Dodgeb4ya Posted February 27, 2013 Report Share Posted February 27, 2013 A good auto/truck machine shop person is one to be consulted on this issue as they deal with it day to day. Quote Link to comment Share on other sites More sharing options...
Powerhouse Posted March 1, 2013 Author Report Share Posted March 1, 2013 (edited) I found on a hudson website in the engine rebuild instructions that the clearance should be .003. Also found that rod balance for them was within 7 grams or .25 oz. link is here: http://home.comcast.net/~sarahdyoung/hudsonjetengine.html Edited March 1, 2013 by Powerhouse Quote Link to comment Share on other sites More sharing options...
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