Tagless Big End Bearing Shells

Tagless Big End Bearing Shells

Author
Discussion

ukkid35

Original Poster:

6,138 posts

172 months

Thursday 1st December 2016
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I've ended up with some tagless shells, but the originals in my M160 Smart engine probably have tags.

It seems like there are a lot of tagless shells for sale, especially for smaller engines.

The brand I have is King, which seem to get rave reviews on some sites such as the US Scooby forum.

Should I just put them to one side, or perhaps just fit the lower shell if the upper looks ok?

Any experience of using King or tagless?

Mignon

1,018 posts

88 months

Thursday 1st December 2016
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Looking at their online catalogue they list CR333CP which have tabs and CR334CP which don't and also CR337CP which have three shells with tabs on the left and three with tabs on the right. They all appear to reference to the same engines but you have to assume there are differences in the engine machining during production. I'd see what you have fitted at present and stick with the same.

I've never come across tabless shells but it seems like a damn stupid idea for the sake of a few pennies. King bearings are superb though. I found their aluminium based material very durable.

ukkid35

Original Poster:

6,138 posts

172 months

Thursday 1st December 2016
quotequote all
Thanks, good to know King are well respected.

One thing I didn't mention is that I'm not doing an engine rebuild, I'm replacing the timing chain and need to remove the sump, so it's more of a WhileYou'reAtIt.

HJG

461 posts

106 months

Friday 2nd December 2016
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Tagless shells are more common now. It saves money on both the shell and the rod.

In the vast majority of engines, their only purpose is/was to control the shell's axial position during installation.

In high RPM engines, the tags are sometimes relied upon to prevent shell rotation where the interference fit itself is not enough. This only works if the slots are designed such that the tags butt up against a 'stop' (i.e. one slot per half of the rod, diagonally opposed to one another)

ukkid35

Original Poster:

6,138 posts

172 months

Friday 2nd December 2016
quotequote all
HJG said:
In high RPM engines, the tags are sometimes relied upon to prevent shell rotation where the interference fit itself is not enough. This only works if the slots are designed such that the tags butt up against a 'stop' (i.e. one slot per half of the rod, diagonally opposed to one another)
Presumably the slots are machined before the big ends are fracture split - or is that manufacturing process reserved for smaller engines like the Smart?

Would that design also not prevent the bearing spinning, does it have to butt up against a stop?

Mignon

1,018 posts

88 months

Friday 2nd December 2016
quotequote all
ukkid35 said:
Thanks, good to know King are well respected.

One thing I didn't mention is that I'm not doing an engine rebuild, I'm replacing the timing chain and need to remove the sump, so it's more of a WhileYou'reAtIt.
It's extremely unusual to find bearing wear on modern engines with today's oil unless you have some specific problem (noise, oil pressure etc) and if that were the case then the mains and a bunch of other stuff would probably need doing too. I'd leave well alone.

ukkid35

Original Poster:

6,138 posts

172 months

Friday 2nd December 2016
quotequote all
Main failure mode for the M160 Smart is stuck oil control rings causing burnt out exhaust valves (probably due to oil change interval or quality). I've repaired four of these and always replace the big end shells while the pistons are out, the lower shell is often through the top layer with copper colour appearing. This particular example hasn't burnt a valve yet (unless someone's been there before) but it is the filthiest engine I've seen yet, more burnt on sludge than I've seen since my Capris many years ago. I fully expect the lower shells to be worn through.

HJG

461 posts

106 months

Friday 2nd December 2016
quotequote all
ukkid35 said:
Presumably the slots are machined before the big ends are fracture split - or is that manufacturing process reserved for smaller engines like the Smart?

Would that design also not prevent the bearing spinning, does it have to butt up against a stop?
The fracture split occurs very early in the con rod manufacture. The bolts are then inserted and tightened to production torque before any big end machining. In cheaper engines with a single tag slot machining op (directly opposite on rod and cap) this is done with the rod and cap together. This does not provide a 'stop'.

In higher performance engines the two diagonally opposed slots is almost always done with the rod and cap separated

Mignon

1,018 posts

88 months

Friday 2nd December 2016
quotequote all
I'm surprised such a modern engine even has copper type bearings. The bearing manufacturers have been moving over to silicon-aluminium bi-metal bearings such as King have always made rather than copper-tin and and then a babbit layer tri-metal ones.

The Si-Al has some important advantages. You only need the one layer directly on the steel shell and it can be 10 plus thou thick so if that ever wears out then the engine is way past being toast in every other respect. It actually polishes the crank journal as it runs to reduce friction. The problem with babbit is although it has very good embeddability to absorb debris particles it can only be very thin or it loses its ability to handle load. Maybe half a thou thick up to perhaps just under a thou and then the copper-tin under that.

Many years ago a friend was building his own experimental engine and I supplied the bits for him. Glacier OE type tri-metal bearings of which he munched a couple of the big end shells trying to fit them. I could only get King aluminium bearings at short notice so the engine finished up with 2 Glacier and 2 King big ends as he didn't want to pull apart the rods he'd already got fitted ok. All sorts of things went wrong later including a pinhole in a bore so it ran for ages on mainly water in the sump. He managed to control the amount of water leakage just to get to work and back by running without a rad cap so the cooling system wasn't pressurised and then just driving slowly and it struggled on like that for ages. When it finally gave up the ghost and came apart the Glacier copper babbit bearings were destroyed. The King aluminium ones still looked like new. I was inordinately impressed. I stuck with King ever after.

GreenV8S

30,150 posts

283 months

Friday 2nd December 2016
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ukkid35 said:
stuck oil control rings causing burnt out exhaust valves
I'm intrigued - how does that cause that?

ukkid35

Original Poster:

6,138 posts

172 months

Friday 2nd December 2016
quotequote all
GreenV8S said:
ukkid35 said:
stuck oil control rings causing burnt out exhaust valves
I'm intrigued - how does that cause that?
Oil means it runs hot, exhaust valves don't stand a chance.

What I don't understand is why the spark plugs don't break down first.

227bhp

10,203 posts

127 months

Friday 2nd December 2016
quotequote all
Mignon said:
I'm surprised such a modern engine even has copper type bearings. The bearing manufacturers have been moving over to silicon-aluminium bi-metal bearings such as King have always made rather than copper-tin and and then a babbit layer tri-metal ones.

The Si-Al has some important advantages. You only need the one layer directly on the steel shell and it can be 10 plus thou thick so if that ever wears out then the engine is way past being toast in every other respect. It actually polishes the crank journal as it runs to reduce friction. The problem with babbit is although it has very good embeddability to absorb debris particles it can only be very thin or it loses its ability to handle load. Maybe half a thou thick up to perhaps just under a thou and then the copper-tin under that.

Many years ago a friend was building his own experimental engine and I supplied the bits for him. Glacier OE type tri-metal bearings of which he munched a couple of the big end shells trying to fit them. I could only get King aluminium bearings at short notice so the engine finished up with 2 Glacier and 2 King big ends as he didn't want to pull apart the rods he'd already got fitted ok. All sorts of things went wrong later including a pinhole in a bore so it ran for ages on mainly water in the sump. He managed to control the amount of water leakage just to get to work and back by running without a rad cap so the cooling system wasn't pressurised and then just driving slowly and it struggled on like that for ages. When it finally gave up the ghost and came apart the Glacier copper babbit bearings were destroyed. The King aluminium ones still looked like new. I was inordinately impressed. I stuck with King ever after.
Unless you've already seen it, you might like this: http://kingbearings.com/files/Engine_Bearing_Mater...
Particularly P7.
Glyco now make a 188 bearing which changes hardness through its life, it's soft when new for bedding in and conformity, but then hardens for longer life, it has copper and bronze in it, maybe that is what is used in this Smart engine.
I doubt it's using Sputter which is a bit expensive for a production car.

Mignon

1,018 posts

88 months

Saturday 3rd December 2016
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227bhp said:
Unless you've already seen it, you might like this: http://kingbearings.com/files/Engine_Bearing_Mater...
Particularly P7.
Very interesting. I'd certainly say the conditions my friend inadvertently created were "mixed lubrication" ones. A rather unpleasant frothy mix of oil and water. It's still the only car I've ever known where a normal maintenance operation was to drain a bit out of the sump when there was too much water mixed with the oil in there.

Those were the first King bearings I ever bought. Must be well over 20 years ago. They were crazy cheap, like a fiver a set to trade, so I figured they were crap but as the years have gone by it's been enlightening to find out they were actually better than the competition and now that material is becoming the norm.

ukkid35

Original Poster:

6,138 posts

172 months

Saturday 3rd December 2016
quotequote all
GreenV8S said:
ukkid35 said:
stuck oil control rings causing burnt out exhaust valves
I'm intrigued - how does that cause that?


ukkid35

Original Poster:

6,138 posts

172 months

Saturday 3rd December 2016
quotequote all
Pic from a previous M160, I didn't take a photo of the lower shells, I guess they looked OK to an amateur like me



Edited by ukkid35 on Saturday 3rd December 10:19

Mignon

1,018 posts

88 months

Saturday 3rd December 2016
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That's a very unusual wear pattern. Shells usually wear more evenly over their whole surface.

227bhp

10,203 posts

127 months

Saturday 3rd December 2016
quotequote all
Twin plug head, I like that. What do the pistons look like, are they flat tops?

That bearing failure is interesting too. I suspect it's specific to that engine, has anyone come up with a reasonable explanation as why they wear on just that area? First thoughts are rod distortion, but things are seldom that simple....

227bhp

10,203 posts

127 months

Saturday 3rd December 2016
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Lol, both posted at 10.35.

ukkid35

Original Poster:

6,138 posts

172 months

Saturday 3rd December 2016
quotequote all
227bhp said:
Twin plug head, I like that. What do the pistons look like, are they flat tops?
This is what I saw the last time I took the head off my Smart - I'm sure there's something missing...


227bhp

10,203 posts

127 months

Saturday 3rd December 2016
quotequote all
ukkid35 said:
This is what I saw the last time I took the head off my Smart - I'm sure there's something missing...

Oh dear, did you find it? wink

The other pistons are displaying signs of det at the bottom there (probably caused by the oil contamination), is that det' opposite the corresponding squish pad on the head?