Pulling the Pin
Posted: Mon Feb 17, 2020 9:09 am
Started a rebuild on a Mc 91 and the first thing I was met with was a bad rod. The rod problem is nothing new and it just backs up the thought that these old engines need to be taken apart and given a close inspection before they are run. You don't know what you got till you take a look inside.
Now here is where it got interesting. The piston, bore and rings were in great shape and could be saved so I needed to get the piston off the rod but the style of the piston was the solid bearing pocket out at the exhaust side and I had no access to pull the pin so I had two options, push the pin and the bearing out of the piston on the exhaust side, then re-install the bearing or try and tap the wrist pin and pull it out on the open end.
I didn't want to mess with the pushing the bearing out and then having to re-install it so I decided to pull the wrist pin out on the open end bearing and to do this I was going to tap the wrist pin to allow me to thread in a jack screw set-up.
First thing I did I measured the I.D. of the wrist pin and it was a good candidate for a 3/8" thread diameter. I knew the pin was going to be pretty tough just because of the nature of its use so if I was going to tap it I would need a good name brand hi-speed or cobalt tap and luckily I worked at a tooling distributor in the past and they were able to provide me with a 'Cleveland' brand 3/8"X24 4 flute tap. I went with High Speed Steel because they were out of cobalt, same with the 4 flute instead of 2 but I figured what the hell.
Next thing I did was pack some tin foil down in the wrist pin because I didn't want any metal chips getting into the closed wrist pin bearing as I was tapping, then I tracked down my trusty bottle of Castor Oil tapping fluid from a tech article from days gone by and I was ready to go.
Tap lubed, wrist pin lubed, give the tap a twist. When tapping you can tell right away if your cutting or rubbing and I was met with a nice cut. As I was cutting into the pin I kept very close attention to the flex of the tap and made sure I took small cuts that were very well lubricated.
The tapping procedure went very well and gave me over a 1/2" of nice thread to screw my jack down into.
O.K. first hurdle cleared now its on to building a 'jack' mechanism and I knew the easiest way to build the jack would be to utilize my existing wrist pin push-puller.
My wrist pin puller has a 1/2" inner diameter thread but my wrist pin was tapped to 3/8" so I wanted to sleeve down the inner diameter so I had a better fit on my jack screw so I found a old 3/8" pipe flare nut that had 1/2" OD thread and my needed 3/8" I.D. Next I found a 3/8X24 bolt and nut which would be the jack nut and I threw a washer in between just for good measure.
I heated the whole assembly in my second hand store toaster oven before I tried to pull the pin. Heavy gloves on, I pulled the piston assembly from the oven, threaded the jack screw into the assembly till it stopped turning then I started to turn the jack nut and it pulled the pin right out of the rod. Success !
There you have it, a low buck technique that worked very well however I would not suggest using the tapped wrist again.
See you at THE BIG ONE.
R.E.A.R.
Now here is where it got interesting. The piston, bore and rings were in great shape and could be saved so I needed to get the piston off the rod but the style of the piston was the solid bearing pocket out at the exhaust side and I had no access to pull the pin so I had two options, push the pin and the bearing out of the piston on the exhaust side, then re-install the bearing or try and tap the wrist pin and pull it out on the open end.
I didn't want to mess with the pushing the bearing out and then having to re-install it so I decided to pull the wrist pin out on the open end bearing and to do this I was going to tap the wrist pin to allow me to thread in a jack screw set-up.
First thing I did I measured the I.D. of the wrist pin and it was a good candidate for a 3/8" thread diameter. I knew the pin was going to be pretty tough just because of the nature of its use so if I was going to tap it I would need a good name brand hi-speed or cobalt tap and luckily I worked at a tooling distributor in the past and they were able to provide me with a 'Cleveland' brand 3/8"X24 4 flute tap. I went with High Speed Steel because they were out of cobalt, same with the 4 flute instead of 2 but I figured what the hell.
Next thing I did was pack some tin foil down in the wrist pin because I didn't want any metal chips getting into the closed wrist pin bearing as I was tapping, then I tracked down my trusty bottle of Castor Oil tapping fluid from a tech article from days gone by and I was ready to go.
Tap lubed, wrist pin lubed, give the tap a twist. When tapping you can tell right away if your cutting or rubbing and I was met with a nice cut. As I was cutting into the pin I kept very close attention to the flex of the tap and made sure I took small cuts that were very well lubricated.
The tapping procedure went very well and gave me over a 1/2" of nice thread to screw my jack down into.
O.K. first hurdle cleared now its on to building a 'jack' mechanism and I knew the easiest way to build the jack would be to utilize my existing wrist pin push-puller.
My wrist pin puller has a 1/2" inner diameter thread but my wrist pin was tapped to 3/8" so I wanted to sleeve down the inner diameter so I had a better fit on my jack screw so I found a old 3/8" pipe flare nut that had 1/2" OD thread and my needed 3/8" I.D. Next I found a 3/8X24 bolt and nut which would be the jack nut and I threw a washer in between just for good measure.
I heated the whole assembly in my second hand store toaster oven before I tried to pull the pin. Heavy gloves on, I pulled the piston assembly from the oven, threaded the jack screw into the assembly till it stopped turning then I started to turn the jack nut and it pulled the pin right out of the rod. Success !
There you have it, a low buck technique that worked very well however I would not suggest using the tapped wrist again.
See you at THE BIG ONE.
R.E.A.R.