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neilca's Avatar
 
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Piston Pin Clips

I am in the process of restoring the top end on my 2.4. When I first assembled it I could not install the J&E clips supplied with the pistons. I used some old Porsche clips instead. I didn't have a problem with these clips but since I have it apart I am revisiting these clips. The part number is 866-063 MW. This appears to be the correct part but I suspect they are too big.



I machined a tapered tube to compress the clip down the required diameter of 22mm, as you can see there is very little gap on this clip. This is about a 0.050 gap where the Porsche clip has about 0.250 of gap.

Is this what they should look like?

Old 11-17-2013, 01:19 PM
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I don't see how a slightly larger gap is going to be a problem. It is not like the clip expands more than the aluminum piston, is it?

Is the wire diameter of the Porsche clips the same as that for the J&E? I hate the J&Es. Despite having the Stomski tool I sweat getting them in. Removing them is even worse, and I can see from marks on the pistons of the motor I bought that the guy who built it had issues as well.

I don't understand why a square edged clip holder in the piston, and a common circlip with ears so you can use normal circlip pliers for install and removal, would somehow not securely hold the wrist pin in place. And no fuss R&Ring. Are the wire clips that much less expensive?
Old 11-17-2013, 08:17 PM
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My problem with the gap is that I cannot compress the clip to the 21mm necassary to use an insertion tool. The hole in the picture is just a fuzz over 22mm. When I tried the Stomski method the ends overlapped and the clip bent in the center where I pushed it down with the screwdriver.
Old 11-18-2013, 02:11 AM
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The clip is bigger than the Stomski tool but it will deform inside the tube but it still inserts properly and it sure is easier than any other method.
I have to agree with Walt, ears and circlip pliars would be easier.
Bruce
Old 11-18-2013, 04:27 AM
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I asked the same question why nobody uses inny style retaining rings. HawgRyder gave a good answer- see post #27

Most difficult engine building job........
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Old 11-18-2013, 12:37 PM
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Here is what Bob said:
"ID circlips have those little extra tabs which have mass.
If the clips are in the wrong position...as the piston goes up and down the weight of the tabs loosens the clip in the groove and lets the circlip fall out."

Bob has a lot of practical experience, and this connects the dots.

But while the tabs do have mass, it is hard for me to believe they have enough to counteract the "springiness" which holds the clips in place to start with. It would only be the extra mass of one tab in play, too, as the other tab's extra mass would hold its side of the clip more firmly into the groove - but not so much more firmly as to also distort things.

If I have some extra idle time, maybe I'll weigh a circlip, calculate the area of a tab, get a figure on how many Gs say 10,000 rpm might raise that figure. And then come up with a way of measuring the spring action, to see how much that extra force, in just the wrong position, would make one side of a clip move. That might be the hardest measurement to make, unless there are engineering specs for these things one could use.
Old 11-20-2013, 11:16 AM
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I sent this same picture to J&E and got a response yesterday. They say it looks normal to them and they do not recommend using an insertion tool. So I asked how the hell do you install these.

Either way I am not using them. I am going to use the Porsche clips. In my 40+ years of playing with cars I have seen one c clip come out of an engine while it was running. That was a Triumph 650 cc bike. I suspect my buddy just didn't install that one correctly.

I agree with Walt I do not see the mass of the rings on the clip to be significant enough to cause failure. I can believe someone built an engine where there was inadequate spring tension and it was blamed on nebulous physics.

Has anyone really seen a c clip fail? Have we attempted to fix something that doesn't exist?
Old 11-20-2013, 12:28 PM
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I would think that the piston makers like JE and others would use a time-tested clip like the internal retaining ring if it proved to work. Maybe its the square cross section that they don't like? I suspect the round section of the c-clip is easier to utilize in terms of machining the groove.
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Old 11-20-2013, 12:53 PM
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Back in the old days (really old) the wrist pins were secured by a bolt through the small end of the rod.
This ensured the centering of the pins...but made the pin/piston joint responsible for the bearing surfaces.
Full floating pins are the answer to the problem...which is how to distribute the bearing loads to muliple surfaces.
In an ideal situation...the pins would stay centered and the 3 surfaces would share the load nicely.
In drag engines...we found that putting Teflon buttons in the end of the hollow pins (to position the pin side-to-side) was the ultimate answer...no clips...easy to install...and no chances of cylinder damage.
With the design of most pistons...the Teflon buttons will need to have a long tail...with a small contact area to touch the bore...and be unable to be pushed out of place.
Even in some of the more radical designs of pistons...where the pin holes are "retracted" from the bore...this might still be possible.
If the Teflon buttons look like they are going to be too long...perhaps a design where the button itself is held in place by an exterior fastener or device might work.
I have looked at the overall problem...and for those types of pistons...maybe a block of Teflon that mimics the curve of the piston...with a tail going into the pin hole might work.
Bob
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Old 11-20-2013, 01:18 PM
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I did have a circlip failure, but it wasn't the kind we are worrying about here.

One of the two tabs on one clip broke off while the engine was in use. Because the piston had just a recess for the pin, the little broken piece couldn't just fall harmlessly down into the sump. Instead, it bounced around, etching the cylinder. And for grins, it would periodically travel through the hollow pin, and do the same on the other side. Which is why I have 5 perfectly good, albeit old, 90mm Arias pistons in my stash.

Why that tiny piece broke off, given that there are really no forces exerted on the tab, has always been a mystery. But no question, it did break off.

The pin, however, stayed put as intended - the clip did its retaining job just fine.

I think "slipper skirt" may be the term for the kind of piston where Teflon buttons won't work, leading to Bob thinking of an interesting way of doing that, albeit one where using a short Teflon cylinder to hold a larger piece of Teflon in place could be problematic as far as shear strength goes.
Old 11-20-2013, 03:10 PM
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Walt...I think you and I have the same thoughts...would a piece of Teflon...say round bar style...long enough to go from on side of the bore to the other...with a step on each side to capture the pin laterally..and obviously in two pieces for install purposes..be strong enuugh to do the job.
My thinking is ...if the Teflon touching the walls of the cylinder were small enough (to reduce the friction) then perhaps it would work.
There would be almost no side thrust to the Teflon to cause a break...and the steps in the piece would stop the pin from shifting sidways.
If the Teflon piece were built like those book screws (they have a male/female joint in the middle) it might work.
You would locate the pin on the Teflon bar...screw it together...and then push the whole assembly in to the piston.
Once the piston was inserted into the bore...no possible side shift could occur.
Bob
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Old 11-21-2013, 03:28 PM
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For non-slipper skirt pistons, I can see the buttons. Easy where the pin hole is continuous all the way out to the edge. And for pistons with a slot, so to speak, with the end of the pin hole down a ways into the slot, you could mold a piece with the radius of the cylinder to fit the slot, with a round piece sticking out into the pin hole.

But the slipper skirts have the pin hole what - maybe an inch in? I'd be reluctant to try to have a cylindrical piece (turned down to a smaller cylinder where it fits inside the pin) sticking out that far unsupported. You could form all this so it reached upward to touch the top of the piston, which would support it on the downstroke. You could even have it have the same kind of radiused edge as if there were a slot there. But on the upstroke I'd think you'd put a bending force on the small cylinder which sticks into the pin.

But wait, you could perhaps insert a steel tube, so it was what stuck into the pin center, and stuck out until 1mm or so from the cylinder wall. Maybe that wouldn't tend to bend.

But now for sure you are adding more weight than any kind of clip to the assembly.
Old 11-21-2013, 04:44 PM
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Don't ya just hate it when someone gets practical?
You are correct of course Walt...the weight is the problem.
I think we should start a movement to outlaw all slipper skirt pistons...that would solve the problem...LOL
Bob
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Old 11-22-2013, 08:43 AM
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Saw the QSC pistons in this lovely thread use internal retaining ring circlips

Pistons QSC 2,7
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Old 12-12-2013, 06:05 AM
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The weight of the circlip ear/tab end will slowly fatigue to the point of failure. The acceleration/deceleration of TDC and BDC puts tremendous strain on the entire piston assembly including ring-lands which we see as a more common first point of failure when the more reliable ring clip is used. Kinda like the reason why you don't keep your ball in the trunk between bowling matches. If you drive long enough that bowling ball will work it's way out of the trunk.
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Old 12-12-2013, 06:53 AM
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When you say ring lands, I believe you're referring to the piston pin boss/bore section of the piston since in that same statement you're speaking of the more reliable round section pin clip? Ring land term is typically associated with the upper and lower flat areas of the piston ring grooves.

My bowling ball is in a carry case so it won't roll around.
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Old 12-12-2013, 06:58 AM
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I did mean the ring lands as the rings will have the same force at TDC and BDC and will work the piston along those flats. When overhauling an older engine with high miles it's a good idea to check the ring space in that gap (parallel with ring land) with a feeler to ensure the piston is not worn beyond spec. If it's beyond spec then the piston can crack.

But good point - there can be wear in the pin bore but not normally like you see where items are a bit looser. The surface between the piston and pin is usually sufficient enough to spread the load out and with lubrication keep things from wearing to a noticeable degree. Many higher HP engines such as turbocharged above 200hp per single 20mm pin will actually see the pin deform into a slight arch towards the cylinder head. It's another level of extreme that most won't see but is out there. The solution to increased power then becomes custom oversize diameter pins and related pistons/rods.



As far as running Porsche clips in JE Pistons - you might get away with it and you might not. The wires are different diameters and it may be inviting for the Porsche clip to sneak out of the wider JE groove. You'll probably also notice the pin will sloppier side to side once captured in the piston with both clips installed.

Here's how I was able to insert my JE clips with no hassle:
Specific Question - ARP Head Studs on 2.7 Magnesium case - Insane?

I encourage you to give it another go with the JE clips - you'll sleep better at night.
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“Of the value traps, the most widespread and pernicious is value rigidity. This is an inability to revalue what one sees because of commitment to previous values. In motorcycle maintenance, you MUST rediscover what you do as you go. Rigid values makes this impossible.”
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Old 12-12-2013, 08:03 AM
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I used the Porsche clips. The J&E system is just ridiculous. I may rethink this when I loose my first clip. They two clips are the same wire diameter.

BTW I did make a tool similar to the one in the post. Didn't work.
Old 12-12-2013, 01:31 PM
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I recently built an engine for my '71 Corvette. Used SRP pistons (made by JE).
The answer I got from the machine shop was "You just gotta find the method that works for you".
I put a circlip in one side of the piston, past the groove. Used a small screwdriver to rotate it close to correct orientation. Inserted wrist pin into far side of the piston, and pushed. The action would finish squaring up the circlip, which then popped into the groove.
The second circlip was a bit trickier. I would start a circlip into the bore, with one "end" of the circlip sticking out. We got a piece of some heavy walled SS pipe that was slightly less than the wrist pin bore's diameter, and about 12-14" long. We cut a notch crossways in one end of the pipe, kinda like cutting a wedge out of the pipe. Filed a face on the inside to increase contact area with the circlip. With the notch positioned on the free end of the circlip. I could rotate the pipe, which compressed the circlip, and pushed in on the pipe to install the circlip in the groove.
After the first two, I had the timing down on the motion, and assembled the rest of the pistons with relative ease. So it kinda ended up like the machinist said...we found the method that worked for us.
I don't have a good photo of the hunk of pipe, but you can see it in the pic below on the bench:

Hope this might help someone!
Carter
Old 12-13-2013, 05:28 AM
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Oh, and the 'Vette motor is a real beast: >500 horse and torque, all forged and lightweight. Spins up quick. Hyd roller cam done at 6500rpm. Shoulda gone solid!!

Carter

Old 12-13-2013, 05:31 AM
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