Seems like this is perhaps my only option to make something "off the shelf" work. Is this an acceptable way to do things, is there any adverse affects on engine wear? My connecting rods have a diameter of .975, most of the pistons available with the correct diameter and compression height are .927. How is this done? bushing pressed into the connecting rod? What are they typically made of? Can you buy them somewhere or does it have to be done at a machine shop?
Any "competent" shop should be able to do this for you. Basically...done all the time to "full float" wrist pins that came from the factory as "pressed in". Many are bronze, pressed in and final honed (fitted !) to fit the wrist pin. The engine application and materials will dictate the oil clearance (normally in the .0007/.0009 range for a street engine). Mike
Full floating pins also require some way to hold the pin in the piston. Either a nylon button between the end of the pin and the cylinder wall (drag race stuff, probably not recommended for street use) or the piston needs snap ring grooves in the wrist pin holes to keep the pin from walking out. This usually means a more expensive piston.
Of course, Chevrolet did this with the original Z-28, 302 engines; only they did not bush the rod end. It was direct, slip contact between the rod end and the pin (you already have too much clearance for that to be done). As already mentioned, there has to be a way to retain the pin in the piston. You can get Speed Pro and KB pistons, both hypereutectic and forged, that work with pressed or full floated pins, fairly cheap. For the amount it will cost to rebuild your current rods, you could buy a set of after market Eagle/Scat/XYZ brand replacement rods, or even rebuilt factory rods, from that auction site we all know and love. Butch/56sedandelivery.
The back of the Sealed Power Engine catalog (and others) used to have parts listed in order of size. " Progressive size " listings. it was easy to look for pin bushings (or any other parts) that could be used for projects. I'd expect a replacement bushing already exists that can be used with minimal rework to be a press fit in the rod eye. 0.927" sounds like SBC wrist pin. The best way to finish the pin bore is align boring it parallel to the finished big end bore to create a 'straight" rod. Assumptions about accuracy of the rod side faces or the original pin bore are dangerous. It is desirable to have 0.020" or more material in bushing bore. With enough material it is possible to equalize the lengths of the rods too. Just finish honing the installed bushing follows the original bushing bore with no control of rod length or straightness. Tobin Arp is one company that made machines for align boring rod bushings. Ours had nicely made expanding mandrels that gripped the big end bore directly. http://www.rhynecompetitionengines.com/assets/images/db_images/db_shop_0221.jpg Probably should add some oil holes to the rod eyes. There used to be plenty of theories of right and wrong ways to do that. Original 426 hemi had no holes as I recall.
Just another opinion; Unless you plan on taking the pistons off of the rods often, there is no advantage in having full floating pistons. With each additional clearance point, you give the piston more chance to rock sideways in the bore. You could just have your rods honed to the correct size to fit the .927 pins and have the pins installed as a press fit.
Yea for sure honeing it smaller is a damned good trick. Bushing the rods is fine when done by a competant machinist, take them to the machine shop and have them bushed and fit. Done deal.
I realy like to se that machine that can hone down the hole from 975 to 927 must be some new fantastic invention
Wow, you've got a magic hone that can make holes smaller? The OP has rods has a small end diameter of .975 and he wants to bush them to use pistons with a .927 pin diameter.
I have found a rod that has a .912 diameter end, whats your thoughts on honing/boring them out to .927? 15 thousandths.
It would depend on how much meat you have to work with. If I looked at it and it was not going to be any different than a bushed rod and I had them to use I would just hone the rods and run with it. The thing is that what you are talking about is a floating wristpin, correct? the pistons have keepers? If that is the case it is not a press fit and you will need to give yourself some clearance for the wrist pin so it will be more like .017 and not .015.
This is the HAMB, and you know we like photos. But in the absence of that, at least fill us in on some details! What engine combo are you trying to build? Just really curious!!!
Hey, I wear glasses fer a good reason, also my reading compression isn't up to snuff on all occasions either. That was one of my dumber reading errors. By the way, I used to run a Tobin Arp rod boring table back in the 70's so I know how hard it is to shrink a hole.
LOL, I don't have any pictures.......I am trying to piece this thing together before taking the plunge and spending the money. I am building a Ford 300 inline 6. Rather than use the stock 300 rods, the plan is to use longer 240 rods and a shorter piston, a small block ford stroker piston (331 or 347). That will give me a nearly identical compression distance and improve the rod ratio, reduce wear, and maybe gain a little more torque while I am at it. The 240 rods had 2 options, .975 and .912 wrist pins depending on years. I can find .912 stroker pistons that are forged......I just don't think the extra money getting them is worth it. Hyper's are cheaper and should hold up fine for what I am wanting but most come with the more common .927 pin.
Without having the rod in my hand to measure the ends, that would be foolish to speculate. However, yes possible to hone them to pin fit for a pressed pin. You will generally run into a issue with integrity and strength if you try and make them floating and open up the small end for the O.D. of the appropriate sized bushing. In the old days, some engine builders would run a non bushed full floating rod end, but this after careful placement of oiling holes and only generally for short track use.
Ok, nobody flame on me for digging up a four year old post but... I am doing the EXACT same thing and attempting to locate a wrist pin bushing to fit the .975 rod so I can use small block FORD size pistons/pins @ .912 and every major hot rod company caters nearly ONLY to chevy parts... not dissing chevy, I just do not want anything chevy in my Ford! TLMARTIN84 - did you ever solve the issue? What did you come up with? or anyone else that has done this please chime in, unless you're dead set about convincing me to do something else then please no comment. Thanks for any help!
Hahaha! Don't be silly. All he needs is to stick the .975" pins in a lathe and machine down both ends to .927
Ford 240 and 300 rods in the 60s used .912 sbf pin size later went to .975 early rods will easly go to .927 sbc chevy size. plus by offsetting the pin you can change the length a little. A 350 6" rod piston would be close. Or if you want to use a bushing a Y block bushing could be made to work.
Using the 240 rod on the 300 crank there is only 1.2153 CH left, I was looking at using the ford stroker pistons but I wanted floating pins... hence the reason for the bushing and the .975 rod so reaming isn't hopefully not needed as much to run the .912 pin (leaves more meat on small end of rod). Whole idea is to reduce piston weight/size and longer rod less angle (stronger) especially when running higher compression and high duration bumpstick. I just need to find a company that lists all their floating pin bushings by size, find the right one or close and buy. If this was a smallblock V8 that would be easy... but it is not. I have a set of the early rods, but I want floating pins and the early rods are a lot thinner at the top than the late 240 rod, plus the added bonus of having the oil squirter for the cylinder walls (controversial, some say no hole more oil to crank). Anyhoo, I guess I am left with just keep digging. Thanks.
I bushed my olds rods for Chevy wrist pins that were smaller. I full floated them and used bushings that were for a Wisconsin engine, found by size. They fit the rod and needed honing on the inside. Gary
Thanks roadster1927! Never thought about looking into the stationary engines! I Finally found some last night! 272/292 ford V-8 bushings, their a tad on the long side but id/od is correct! Hopefully they'll work out.
The Jalopy Journal
