CMB RS Style Wrist Pin Circlip Installation

[Timbo Whalen]

G'mornin' everyone....

We're having a devil of a time trying to install a new wrist pin circlip on a CMB 67 twin plug RS style engine.

Never had an issue on the 45 and 91/101 series RS engines...this 67 appears to have a steeper exhaust port floor that's making access more troubling.

In the past, we've made a plunger type apparatus from brass tubing and the plunger from music wire, slip fit into tubing.

The issue seems to be finding brass tubing with ID/OD config to get correct match with wrist pin bore in piston. Stock K&S sizes work for 45 and 91/101 engines, but this 67 seems to have a bastard size wrist pin, comparatively.

Any suggestions out there?....hoping Andy Brown sees this, as I know he's got plenty of experience with this particular engine.

Thank you all, in advance.

 

[Daniel's Racing]

Can you situate the clip in the pin bore carefully with curved hemostats as you roll the piston and kinda use the liner edge to push the rest of clip into the pin bore then back to get access again and carefully use something to pop it into it's groove.

I do not have expirience with the .67 you have and that isn't my normal way I have just heard of people doing something like that to get clips in.

 

[brad nichols]

K&S also makes metric tubing maybe that would work?

 

[John Beardslee]

Tim,
What’s the O.D. of the pin? SAE and International? McMaster Carr sells brass tubing in metric sizes
John

 

[John Beardslee]

Can you situate the clip in the pin bore carefully with curved hemostats as you roll the piston and kinda use the liner edge to push the rest of clip into the pin bore then back to get access again and carefully use something to pop it into it's groove.

I do not have expirience with the .67 you have and that isn't my normal way I have just heard of people doing something like that to get clips in.

Daniel, on these engines you have to work through the exhaust port to insert the wrist pin and the retaining clip. They are a bugger! When I came back racing ten years ago that was the one factor that made me buy 91vac’s instead of the RS 91’s. All it took was Stu explaining the process to me one time to make the decision.
John

 

[Timbo Whalen]

Can you situate the clip in the pin bore carefully with curved hemostats as you roll the piston and kinda use the liner edge to push the rest of clip into the pin bore then back to get access again and carefully use something to pop it into it's groove.

I do not have expirience with the .67 you have and that isn't my normal way I have just heard of people doing something like that to get clips in.

I tried doing that, with no luck....as mentioned, the exh duct cast into the case is unique compared to 45 and 91/101 scheme- tighter window to work within.

Bought some new materials today, so back to the drawing board with a plunger style intent.

This deal makes me wonder how they do it at CMB...if they use dedicated tooling, it would be logical to offer as a purchaseable service tool....Novarossi did that.

Thanks for the input, Daniel.

 

[BigChuck]

Timo... Joe Warren built a tool for this a few years ago. Check with him if he has a extra.
It is a not brainer with this.

 

[Timbo Whalen]

Tim,
What’s the O.D. of the pin? SAE and International? McMaster Carr sells brass tubing in metric sizes
John

Not sure, offhand, John....that's good intel regarding M-C....I knew they carried the K&S line.

Stu and I chatted about it today and I've used same methods he uses on the 45 and 91/101 series RS engines.

The cast-in exh duct is unique on the Evo 67 twin plug...the round outlet is positioned lower, on the vertical, relative to actual exh port, thus the floor in the duct is a steeper angle resulting in a smaller window to work within.

We'll get it!....the REAL issue is that patience seems to wane with age...lol.

Thanks, John.

 

[Timbo Whalen]

Timo... Joe Warren built a tool for this a few years ago. Check with him if he has a extra.
It is a not brainer with this.

Thanks, BC....yeah, it's a simple tool....we're making one now.

 

[ianfolkson]

Cmb factory do it by trapping clip in bottom of hole by lowering piston a little and then rotating crank to the chamfer on the top of the exhaust to push clip in with help of a non magnetic tapered thin rod. The staff lay out a whole line of motors ready for clips and Mauro goes along and puts them in. Each motor takes him a few seconds.

 

[Alan Elzer]

Tim
can you sand the end of k&s tubing to a taper outside in. Till it starts into wrist pin hole in piston thin I use 2 smaller sizes of tubing inside the tapered ended tube to push clip in. I'll look for a picture of what I use for the 45 EVO MOTOR

 

[Timbo Whalen]

K&S also makes metric tubing maybe that would work?

Hmmm, was not aware of that, Brad....on the sealed on a card 12" pieces of K&S, they do print the metric equivalency, and on the red storage tubes for the 3' pieces.

 

[Timbo Whalen]

Tim
can you sand the end of k&s tubing to a taper outside in. Till it starts into wrist pin hole in piston thin I use 2 smaller sizes of tubing inside the tapered ended tube to push clip in. I'll look for a picture of what I use for the 45 EVO MOTOR

Yes, Alan, that's exactly what we've done in the past.... there's something odd about the Evo 67 in comparison to the 45, 91/101 series.

We're making a new tool today from different size tubing we didn't have in stock.
For pin removal, we've just always used a thru tap...as long as it grabs a bit of the pin threads, you're good to go.

Roman the Russian made a video a few years back on bearing replacement in a 91 RS....however, he stopped short of illustrating the circlip reinstall. (See below)

On another note, it appears the OEM circlips have burrs on the snipped ends....when pushing down the brass tube the clips generate brass shavings and take them into the wrist pin pocket. We've learned to simply deburr the ends of the clip, and use a light weight oil in the brass tube.

Thanks for your input.

 

[Timbo Whalen]

Cmb factory do it by trapping clip in bottom of hole by lowering piston a little and then rotating crank to the chamfer on the top of the exhaust to push clip in with help of a non magnetic tapered thin rod. The staff lay out a whole line of motors ready for clips and Mauro goes along and puts them in. Each motor takes him a few seconds.

Thanks, Ian....indeed, seems like that falls into the category of 'practice makes perfect'....we had tried it from the opposite perspective- trapping at top (exh) first, then rotating toward BDC. Clip kept jumping out. As you mention, a non metallic rod with, perhaps, a little notch in the work end, would achieve greatest efficacy.

Can't tell you the number of times we've wondered, 'Hmmm, wonder how CMB does this in production.'

Again, thank you!

 

[Daniel's Racing]

Daniel, on these engines you have to work through the exhaust port to insert the wrist pin and the retaining clip. They are a bugger! When I came back racing ten years ago that was the one factor that made me buy 91vac’s instead of the RS 91’s. All it took was Stu explaining the process to me one time to make the decision.
John

Yes I realize how they up in the exhaust port. Had 3- 1.01 RS engines as my last hurah with nitro. I never had any trouble getting the clips in them but had the right size tubing to insert them with. There were guy's doing it the way I mentioned too so I thought if tubing size is the issue with that method on the .67 he could try that method.

I think he said he tried and just too tough on .67.

He is back to tubing hunt for proper sizes.

The 1.01 RS clip is 5 second install once clip is loaded in tube and ready.

Yes, Alan, that's exactly what we've done in the past.... there's something odd about the Evo 67 in comparison to the 45, 91/101 series.

We're making a new tool today from different size tubing we didn't have in stock.
For pin removal, we've just always used a thru tap...as long as it grabs a bit of the pin threads, you're good to go.

Roman the Russian made a video a few years back on bearing replacement in a 91 RS....however, he stopped short of illustrating the circlip reinstall. (See below)

On another note, it appears the OEM circlips have burrs on the snipped ends....when pushing down the brass tube the clips generate brass shavings and take them into the wrist pin pocket. We've learned to simply deburr the ends of the clip, and use a light weight oil in the brass tube.

Thanks for your input.

Those burrs on the ends need to be there to dig into the OD of the groove. It's stop's the clip from spinning in the groove. If a clip spins and the gap is not top or bottom (and never with clip gap in access gap you are asking for a bad day.

If it's gap is not straight up or straight down you risk the clip coming out.

Seems crazy but at he speed the piston changes direction and even though the clip is so light they have been known to come of and that is positively the reason. The clip collapes enough for pin to dislodge it. Ask me how I know. I lost a RS piston and liner by doing just that. Don't smooth the ends for sure.
Ever see a gas engine clip come out look at clip on the other side and you will always see they put gap at the side every time. They can/will come out.

You should actually try to spin see if clip will move in the groove with a small screwdriver or pick and it should never be able to be pushed by either end as the other end should be digging into the aluminum so hard it will not move at all. If you can move it the clip is trash.

You will always find that sharp burr of the edge of a wrist pin clip to hold it where you put it.

Surely they would come with rounded ends if it were for the fact it will cause them to come out.

Spiral wound clips are neat. Install easily with tube method and end locations do not matter.

https://www.designworldonline.com/smalley-spirolox-retaining-ring-vs-stamped-circlip/

 

[Timbo Whalen]

Yes I realize how they up in the exhaust port. Had 3- 1.01 RS engines as my last hurah with nitro. I never had any trouble getting the clips in them but had the right size tubing to insert them with. There were guy's doing it the way I mentioned too so I thought if tubing size is the issue with that method on the .67 he could try that method.

I think he said he tried and just too tough on .67.

He is back to tubing hunt for proper sizes.

The 1.01 RS clip is 5 second install once clip is loaded in tube and ready.


Those burrs on the ends need to be there to dig into the OD of the groove. It's stop's the clip from spinning in the groove. If a clip spins and the gap is not top or bottom (and never with clip gap in access gap you are asking for a bad day.

If it's gap is not straight up or straight down you risk the clip coming out.

Seems crazy but at he speed the piston changes direction and even though the clip is so light they have been known to come of and that is positively the reason. The clip collapes enough for pin to dislodge it. Ask me how I know. I lost a RS piston and liner by doing just that. Don't smooth the ends for sure.
Ever see a gas engine clip come out look at clip on the other side and you will always see they put gap at the side every time. They can/will come out.

You should actually try to spin see if clip will move in the groove with a small screwdriver or pick and it should never be able to be pushed by either end as the other end should be digging into the aluminum so hard it will not move at all. If you can move it the clip is trash.

You will always find that sharp burr of the edge of a wrist pin clip to hold it where you put it.

Surely they would come with rounded ends if it were for the fact it will cause them to come out.

Spiral wound clips are neat. Install easily with tube method and end locations do not matter.

https://www.designworldonline.com/smalley-spirolox-retaining-ring-vs-stamped-circlip/

I can't agree with that....the spring tension along with near net zero fit between spring wire gauge size and the annular groove in the wrist pin bore is more than sufficient....the circlip is going nowhere.

In the case of the CMB circlips it's all about cost.

 

[Timbo Whalen]

Cmb factory do it by trapping clip in bottom of hole by lowering piston a little and then rotating crank to the chamfer on the top of the exhaust to push clip in with help of a non magnetic tapered thin rod. The staff lay out a whole line of motors ready for clips and Mauro goes along and puts them in. Each motor takes him a few seconds.

Well, tell ya what....the Mauro Method is a no go for me. It would be interesting to see him do it, and especially the circlip orientation he starts with.

We did get the clip in....it took about 15 secs, and we could optimize the tooling with a hardened steel tube with proper ID/OD configuration, and a knife edge chamfer feature to lead-in and center everything up.

The tool is similar to one we made for the 91/101 engines, and also similar to the one Alan was so kind to illustrate.

A small set of hemostats (metal) is used to load the clip into the tube- less than 10 secs, and another 5 to tap the music wire rod, pushing the clip home.
It's foreseeable to load the tube with several clips if one were installing them on a production basis. With that concept I can guarantee one could do 25 engines in far less time than it would take using the Mauro Method.

When we get caught up here, we'll gladly do a video to illustrate....I do have a 45 RS EVO w/M1 Tuning Kit that we have to reassemble once some flow enhancements are complete on the sleeve.

A big 'Thanks!' to everyone for participating on this thread.

Tim

 

[David Ashcroft]

My Mrs is my go to for clip installation she installs them easily,save me any frustration..

 

[Daniel's Racing]

Hmmm, was not aware of that, Brad....on the sealed on a card 12" pieces of K&S, they do print the metric equivalency, and on the red storage tubes for the 3' pieces.

Tim,
There is no metric equivalent for most standard sizes. Some are close I am sure like 5/16" and 8mm. They would be real close but still bet they are off by a few thousands. It is a whole new bunch of tubing in the metric sizes. It all telescopes so it has to be exactly the right size in and out.


Metric is available same way in the short or long pieces.

https://ksmetals.com/collections/300-mm-long-round-brass-tubing
https://ksmetals.com/collections/meter-long-round-brass-tubing

 

[FloridaScaleBoater]

Tim, can you see the top of the exhaust port through the exhaust snout?