150 miles on a new motor and this

I would never let a performance shop build my motor. If the apprentice dues not make sure the circlips are properly seated . . . ? - Even if you are a complete dud as a mechanic, you would probably take better care. With a Commando engine, the only tricky part is the valve gear. It is possible get a pushrod installed wrongly, but everything else is fit and check. The manual is very good, but I don't usually resort to using it.

comnoz said:

piston speed in an F1 engine reaches ~21 MPS.

A Norton hits 21 mps at 7050 rpm.

Click to expand...

Good grief. That’s scary !


@ Pete, hope this gets sorted with minimal fuss, stress and cost. Do keep us posted...

Unless the circlip lands are radiused, why would any design engineer spec wire rather than flat? I'm sure the lands were cut with a square cutter bit. Flat clips fit perfectly and can't possibly cost that much more than the flat types.

If you buy pistons with wire circlips, throw the junk away and get flat clips. Or wait for that giant "POP" and the heartbreak that follows. I'm amazed a "performance" shop doesn't know this.

Danno said:

Unless the circlip lands are radiused, why would any design engineer spec wire rather than flat? I'm sure the lands were cut with a square cutter bit. Flat clips fit perfectly and can't possibly cost that much more than the flat types.

If you buy pistons with wire circlips, throw the junk away and get flat clips. Or wait for that giant "POP" and the heartbreak that follows. I'm amazed a "performance" shop doesn't know this.

Click to expand...

Yep I agree
But we don't yet know if the performance shop fitted the circlips ?

OP said he took the head to the "performance shop that did the work". I guess they could have done the head and the owner did the pistons and rings (and crappy circlips) in which case, he's on his own nickle for the repairs. A hobbyist/owner doing his own work might not be aware of the issues with wire circlips, but any place calling itself a "performance shop" should have known better.

Danno said:

OP said he took the head to the "performance shop that did the work". I guess they could have done the head and the owner did the pistons and rings (and crappy circlips) in which case, he's on his own nickle for the repairs. A hobbyist/owner doing his own work might not be aware of the issues with wire circlips, but any place calling itself a "performance shop" should have known better.

Click to expand...

Yep I agree

comnoz said:

It's more just the fact that due to the long stroke and rpm potential of a Norton the piston speed is in the stratosphere. This means only the best circlips are suitable in a Norton. <...> A Norton hits 21 mps at 7050 rpm.

Click to expand...

A shortstroke (80.4mm stroke) will yield ~18.9 mps (that's m/s) at the same rev. Another reason to consider this configuration.

-Knut

to use flat circlips you MUST have square machined circlip grooves AND flat ends on the wrist pin. a qualty round circlip with the right wrist pin is fine when properly installed.

Danno said:

If you buy pistons with wire circlips, throw the junk away and get flat clips. Or wait for that giant "POP" and the heartbreak that follows. I'm amazed a "performance" shop doesn't know this.

Click to expand...

My pistons came with flat circlips. One set was fine, one set was undersized and fit loose.
It's a shame.

I don't know anything about EMG brand pistons, never having used any. But re round wire circlips...

We used a lot of Mahle, Wiseco, Vertex and other well-known piston brands in engine work. Round wire circlips were typically supplied with the pistons. We never experienced any problems with circlips (of any kind). As noted, you can't use flat circlips in round-wire circlip assemblies or visa versa. But the pistons come with the proper circlips so that should never occur.

If a circlip is mishandled/over-compressed on install, it may not seat firmly in the groove which could lead to 'un-seating' and the type of damage in the pics. Looking at the pic I'd say with confidence that a circlip was incorrectly installed. HOWEVER, I readily admit that Jim's experience with Norton motors is many orders of magnitude beyond mine. Perhaps there is some inherent characteristic with them that causes unusual load on a circlip which could cause failure in less robust circlips.

In the cases where an EMGO circlip in a Norton motor has "failed," how, exactly does it fail? Does the circlip itself break? Does it pop out of the groove? Does it break through the groove wall? Just curious!

I would bet a lot of money the circlip was never actually seated in it's groove.

I have used about 50/50 circlip and wire type, still zero failures with 23 engine overhauls done plus two additional top end jobs to install thin cylinder base plates to lower compression; so 25 top ends.

Without Jim's observations and comments, many of you would conclude that ALL circlip failure is "faulty installation", when it's probably more than one scenario for failures, but the frequency of those failures are caused by the factor Jim mentioned, the commando's piston speed at high rpms.

In my case, I had the wire circlips with the big tangs in the center used to compress them. I think those large tangs cause this type of circlip to compress at high rpms, giving them the potential to pop out of their groove.

Other scenarios can be cut circlips put in backwards allowing them to "walk" out of the groove under pressure from the wrist pin. Undersized circlips have been mentioned, and of course installer error can also a valid cause of circlip failure, but I wouldn't put all circlip failures down to "Installer error", like some of you seem to assume.

I've told my story before here. Mine popped at high rpm... high piston speed. Anyone can say, "You didn't seat the circlip properly and that's why it popped out", and all I can say is, "I think I did", because I'm not going to lie and say that I distinctly remember that I did. I didn't like the looks of the circlips I got, but at the time, I assumed the manufacturer wouldn't give me something that would fail and fuck up my entire rebuild.

The big picture is that it happens to commandos enough that the piston speed could be the reason that lesser quality circlips fail sporadically.

Not to hijack this thread, because I think the Original poster has cut steel circlips, and I had the kind pictured below. I would argue that the circlips pictured below, don't belong in any commando... Jim Schmidt uses a wire circlip with NO tangs and has a bevel on the end of the wrist pin so there's no way the wrist pin can push the wire circlip out of the groove. Those wire circlips make sense to me, but not these...




*** edited to add. In the case of my failure, I'd take that bet Paul...

Plain wire circlips -with no tangs on the end are state of the art -as good as they get.
They require using a pin with a 45 degree bevel on the end that locks the ring into its groove.
It also requires a piston with a relief cut in the side of the pin hole to get a tool in to remove the ring.

Wire circlips with a tang are as bad as they get. They do not work with a beveled piston pin and have extra weight on each end of the ring to help unseat it from the groove.

The JCC/Emgo clips fail because they are soft and do not hold tension. If you can do this with a circlip just by squeezing your snap ring pliers you know it's not hard enough to do the job.

CP Carillo pistons use no tang wire circlips like Jim describes above, first paragraph.
I've got them in the 1360, 102mm stroke.
Piston speed is a fair bit higher than a Commando. It's a quick spooling engine, 6500 rpm comes pretty quickly.
I followed the CP instructions carefully, so far no problem.

Glen

worntorn said:

CP Carillo pistons use no tang wire circlips like Jim describes above, first paragraph.
I've got them in the 1360, 102mm stroke.
Piston speed is a fair bit higher than a Commando. It's a quick spooling engine, 6500 rpm comes pretty quickly.
I followed the CP instructions carefully, so far no problem.

Glen

Click to expand...

That's only 22 mps.

I think the record for piston speed was a 92 Honda v12 at 38 mps. It used buttons to retain the pins.
And it only lasted one race.

Now and then with operator error it will briefly touch the rev limiter at 7 k.
I try not to do this as the piston speed is a worry, but you only get about 2 or 3 seconds per gear if feeling boisterous.
Need to drink more coffee I guess

I wouldn't think piston speed has much to do with the load on a circlip since the force involved is up/down on the pin, not side load but I admit I'm no expert on the particular dynamics involved.

OTOH, depending on any 'out of square' alignment of the piston/piston pin/connecting rod/crankshaft and the bearings involved, there could be considerable side load. Hmmmm....

Thanks for the interesting replies. The circlips are wire without tangs. I installed the pistons myself. I can't swear that I didn't install them properly but I have done this job many times. That type of circlip is obvious when it seats in it's groove. The odd part is the fracture around the wrist pin hole. Never seen that before. I have found 1/2 of the circlip so far. I suppose I will have to split the cases. What started the disassembly was the oil burning and the plug fouling. I suspected an oversize valve guide installed by the shop. The head is there and they are going to remove the valves and inspect.

How was the crankshaft end play? If excessive it could result in unusual side-force on a piston pin/circlip. A bent/twisted con rod could do the same though that doesn't seem likely on a precisely machined motor like a factory Norton!

Yes, I'm being sarcastic! I can't imagine how a bolt-together crankshaft and the phrase "precision machining" could co-exist.

This has happened too many times. If a company sells faulty goods - avoid them. There are higher quality pistons for Nortons available with the best option wire clips (see below).




Some of them are available in low expansion alloy such as the 4032 alloy Wiseco Norton pistons as shown below.




Or Wossner 4032 alloy Norton pistons.



Or Billet 4032 alloy Norton pistons



CP Carrillo and JE also make good pistons with wire clips but only in 2618 alloy which expands a little more but is less likely to crack under detonation. I don't have photos of the Carrillo pistons but Worntorn has a pic in his post above.