nm9stheham
Well-Known Member
Not sure how much this post is worth, as most who are skilled enough to do this sort of thing can figure it out or already know. So purely FWIW:
We needed custom length pushrods for our 340 build and decided to go with Comp Cams field cut and assembled pushrods instead of having someone else do it. This was both for expediency and to learn something new. The pushrod needed to be a ball and cup type, to use with adjustable rockers. The parts were:
Comp Cams K75805: 7.500" uncut length, heavy .080" wall, 5/16" OD, 5/16" ball on one end, hardened, qty=16.
Comp Cams 5C5P-16: 5/16" pushrod cups, hardened, qty=16.
Finshed pushrod weight with these parts is 55 gr, compared to 48 gr for a stock 273 ball and cup pushrod.
I won't describe the measurement to get the final pushrod length; we just used a measurement pushrod pair, and averaged the 2 results, taking care to make sure the cup depth differences were adjusted out(between the measurement p-rod cups and the Comp Cams cups). Then we added .040" for lifter preload.
Things needed to do this:
1. Tool for accurately measuring and marking final cut length of cut of pushrod body
2. Accurately grind the cut ends square and get to final finished length
3. Drill inside the cut end for right final ID size; this needed to be done to get the right interference fit of the cup's press-in stem
4. Holders for pushrods for rough cuts, finish grind, and inside drilling
5. Tool to press cup ends into pushrods
Comp Cams offers a combination bit that will do 1,2, and 3 above, but it is not cheap, and I have read one complaint of it being easy to break. So we bypassed that option.
Ideally, a long and reasonably accurate dial caliper would be good for length; you don't need to be accurate to .001";IMO, final accuracy of around .010" is OK for one's own use, with adjustable rockers. There are variables in lifters and other things which are that large, and the adjusters are there for that. 1 adjuster turn is in the range of .040" or .050", so will compensate a lot of small variations. Just get your target length measurements right to start with.
We did not have a long enough dial caliper and it was Saturday, so we improvised. A hard 1/2" copper tube was cut and finished to the final cut length of the cut pushrods, with the ends accurately squared. This was laid on a flat with one end butted square up against a flat surface. This made the tube an easy and quick go/no-go gauge. It was also an easy tool to use for marking the p-rods for cutting; we just used a single-edged razor blade up against the tube end to mark the p-rods. See Pix 1.
Once marked, the pushrods were put in a small pine block that my son cut, drilled, and slotted, that would grip the p-rod when put in a vice. The the p-rod was cut with a hacksaw and some oil about 1/16" to 1/8" longer than the finish cut marks. Easy.... Pix 2.
To finish the length and square the end, each p-rod was chucked into a battery powered 3/8" drill. The drill was run at about 500 rpm (low speed) and the p-rod end lightly pressed square up against a spinning fine grinding wheel. This quickly squared the ends and ground them to final length. (Thanks to someone here on FABO for that fine method! Wish I could remember who described that one to give them proper credit...) The final length marks around the p-rod could be easily seen while spinning with the drill and so the length could be accurately judged. Quick checks in the go/no-go gauge made it fast to see what adjustments needed to be made. Pix 3 and 4.
Once the p-rod bodies were cut to finished length, they need to have the ID drilled out to about 5/8" depth at the cut end, to get to the right ID for the interference fit of the cup ends. We set up a large, stable block of wood on the drill press and bored a deep 5/16" hole to hold the p-rods for drilling. Then the right drill diameter was selected and the ends drilled down about 5/8". Pix 5.
AN IMPORTANT NOTE ON THE ABOVE: We found the press-in stems on the cups to be quite variable in diameter. 12 of 16 were .172" as they are supposed to be, but 2 were small (.170" or .171") and 2 were large (.173" and .1735"). This is pretty crappy variance for something that has an interference fit of .002" ! So, we selected drill bits to best match up to the large, small, and nominal sizes, and step drilled a couple of holes. We also, sanded the stems as smooth as we could get them, as they are a bit rough. This size variation is a PITA, and is not good quality control on the part of Comp Cams. We adapted so we could get the job done and over with.
Finally, pressing in the cups was done with a deep vise; the ball tip was placed against a piece of soft aluminum to prevent any problems on that end. The cup end was put right up against the vice; the hard steel suffered no marks and the edge on the cup is not critical anyway. I guess you could use a hydraulic press, but the vice gave a better feel for
the operation. Pix 6 (using a 273 p-rod to illustrate)
Sanding the cups' press-in stems so they will go part way into the p-rod ID straight is important to getting a good press-in without any bending of the cup stem. We also beveled the ID of the open p-rod end after drilling to help. We used a bit of penetrating oil as a lube for the press operation. It all went well for 15, but the 16th (one of the oversized stems) was hell....I WON'T describe the torture we put that one through, but thank goodness these use hard steel and are thick wall rods!
So it went OK, and we are pleased with the result. Looks like we have one finished pushrod (2nd from the far end in the pix) that is about .015" long. That is <1/3 turn on an adjuster. No problemo.....Pix 7.
I would NOT say this was an operation a rookie BTW; some decent tools and an experienced feel for basic machine work is needed in this process. It took us about 4 hours start to finish, including cutting the go/no-go gauge and holders. Using Smith Brothers would cost us 1.5-2 weeks of waiting with ground shipping from OR to VA, so this was a good time saver for us. We can get the Comp Cams part shipped from stock in OH to us in 1-2 days tops. However, Smith Bro's is a good deal IMO; it would cost us only $40-50 more; add another $30+ for quick shipping to get them in a week. But, we decided to be 'Smith's Country Cousins' on this one!
We needed custom length pushrods for our 340 build and decided to go with Comp Cams field cut and assembled pushrods instead of having someone else do it. This was both for expediency and to learn something new. The pushrod needed to be a ball and cup type, to use with adjustable rockers. The parts were:
Comp Cams K75805: 7.500" uncut length, heavy .080" wall, 5/16" OD, 5/16" ball on one end, hardened, qty=16.
Comp Cams 5C5P-16: 5/16" pushrod cups, hardened, qty=16.
Finshed pushrod weight with these parts is 55 gr, compared to 48 gr for a stock 273 ball and cup pushrod.
I won't describe the measurement to get the final pushrod length; we just used a measurement pushrod pair, and averaged the 2 results, taking care to make sure the cup depth differences were adjusted out(between the measurement p-rod cups and the Comp Cams cups). Then we added .040" for lifter preload.
Things needed to do this:
1. Tool for accurately measuring and marking final cut length of cut of pushrod body
2. Accurately grind the cut ends square and get to final finished length
3. Drill inside the cut end for right final ID size; this needed to be done to get the right interference fit of the cup's press-in stem
4. Holders for pushrods for rough cuts, finish grind, and inside drilling
5. Tool to press cup ends into pushrods
Comp Cams offers a combination bit that will do 1,2, and 3 above, but it is not cheap, and I have read one complaint of it being easy to break. So we bypassed that option.
Ideally, a long and reasonably accurate dial caliper would be good for length; you don't need to be accurate to .001";IMO, final accuracy of around .010" is OK for one's own use, with adjustable rockers. There are variables in lifters and other things which are that large, and the adjusters are there for that. 1 adjuster turn is in the range of .040" or .050", so will compensate a lot of small variations. Just get your target length measurements right to start with.
We did not have a long enough dial caliper and it was Saturday, so we improvised. A hard 1/2" copper tube was cut and finished to the final cut length of the cut pushrods, with the ends accurately squared. This was laid on a flat with one end butted square up against a flat surface. This made the tube an easy and quick go/no-go gauge. It was also an easy tool to use for marking the p-rods for cutting; we just used a single-edged razor blade up against the tube end to mark the p-rods. See Pix 1.
Once marked, the pushrods were put in a small pine block that my son cut, drilled, and slotted, that would grip the p-rod when put in a vice. The the p-rod was cut with a hacksaw and some oil about 1/16" to 1/8" longer than the finish cut marks. Easy.... Pix 2.
To finish the length and square the end, each p-rod was chucked into a battery powered 3/8" drill. The drill was run at about 500 rpm (low speed) and the p-rod end lightly pressed square up against a spinning fine grinding wheel. This quickly squared the ends and ground them to final length. (Thanks to someone here on FABO for that fine method! Wish I could remember who described that one to give them proper credit...) The final length marks around the p-rod could be easily seen while spinning with the drill and so the length could be accurately judged. Quick checks in the go/no-go gauge made it fast to see what adjustments needed to be made. Pix 3 and 4.
Once the p-rod bodies were cut to finished length, they need to have the ID drilled out to about 5/8" depth at the cut end, to get to the right ID for the interference fit of the cup ends. We set up a large, stable block of wood on the drill press and bored a deep 5/16" hole to hold the p-rods for drilling. Then the right drill diameter was selected and the ends drilled down about 5/8". Pix 5.
AN IMPORTANT NOTE ON THE ABOVE: We found the press-in stems on the cups to be quite variable in diameter. 12 of 16 were .172" as they are supposed to be, but 2 were small (.170" or .171") and 2 were large (.173" and .1735"). This is pretty crappy variance for something that has an interference fit of .002" ! So, we selected drill bits to best match up to the large, small, and nominal sizes, and step drilled a couple of holes. We also, sanded the stems as smooth as we could get them, as they are a bit rough. This size variation is a PITA, and is not good quality control on the part of Comp Cams. We adapted so we could get the job done and over with.
Finally, pressing in the cups was done with a deep vise; the ball tip was placed against a piece of soft aluminum to prevent any problems on that end. The cup end was put right up against the vice; the hard steel suffered no marks and the edge on the cup is not critical anyway. I guess you could use a hydraulic press, but the vice gave a better feel for
the operation. Pix 6 (using a 273 p-rod to illustrate)
Sanding the cups' press-in stems so they will go part way into the p-rod ID straight is important to getting a good press-in without any bending of the cup stem. We also beveled the ID of the open p-rod end after drilling to help. We used a bit of penetrating oil as a lube for the press operation. It all went well for 15, but the 16th (one of the oversized stems) was hell....I WON'T describe the torture we put that one through, but thank goodness these use hard steel and are thick wall rods!
So it went OK, and we are pleased with the result. Looks like we have one finished pushrod (2nd from the far end in the pix) that is about .015" long. That is <1/3 turn on an adjuster. No problemo.....Pix 7.
I would NOT say this was an operation a rookie BTW; some decent tools and an experienced feel for basic machine work is needed in this process. It took us about 4 hours start to finish, including cutting the go/no-go gauge and holders. Using Smith Brothers would cost us 1.5-2 weeks of waiting with ground shipping from OR to VA, so this was a good time saver for us. We can get the Comp Cams part shipped from stock in OH to us in 1-2 days tops. However, Smith Bro's is a good deal IMO; it would cost us only $40-50 more; add another $30+ for quick shipping to get them in a week. But, we decided to be 'Smith's Country Cousins' on this one!
