Sludge trap mod...

... or rather ‘sludge trap delete’...

I’m thinking that with modern high detergent oils, and with a quality paper filter in the oil system, that the sludge trap in a Triumph crank is a pretty redundant feature.

Add to that, that it’s probably the most common failure point for broken cranks on one piece Triumph cranks and my thoughts begin to wonder...

I’m thinking that removing it altogether and welding up the threaded plug hole would greatly increase the strength of the crank, and, if using good high detergent oil and a paper filter, I can’t really see a down side to this.

Anyone got any thoughts on this idea ?

The way I see it, if some crankshafts don’t need a sludge trap, then no crankshaft needs a sludge trap.

Do you know where the stress raisers are, that your crank fractures are starting from?

If the threaded hole for the plug is a stress raiser, I really would expect that your welded alteration will be a stress raiser too.

I don’t know the specifics of the stress riser location etc, but I do know the sludge trap hole is a common failure point.

Machining out the threads so the hole was smooth, perhaps with a taper, then welded up using laser welding (zero distortion) ‘seems’ to make sense to me.

Dave Degans somehow got hold of a batch of NOS un-machined Triumph forgings years ago, he machined them without any sludge traps, and they seemed unbreakable.

Hence the welding up idea, just seems like a low cost way of getting a stronger crank. But I’d certainly welcome a more informed opinion...

I asked this very same thing, on this very same forum years ago. The "consensus" ... was to keep it. (... so I did)


However, I agree with the Triton Thrasher statement of "The way I see it, if some crankshafts don’t need a sludge trap, then no crankshaft needs a sludge trap." I don't think I'll bother putting one in on my next Triumph rebuild; modern oils are just that ... "modern." I do like to hear "experts" opinions ... and whatever other owners think though.

Each Norton crank I've stripped was "fairly clean." --- While each Triumph crank I've stripped was, "fairly dirty."

Cheers, Pat

Posed this question to Geoff Collins, local guru whose known for fabricating offset cranks for old brit bikes:

"not worth the effort or risk, just plug it and use a spin on filter"

Last time I inspected my triumph crank the trap was clean, this was after an earlier rebuild where I installed a filter in the return line. Don't think I would bother cracking the plug off ever again

Triton Thrasher said:

The way I see it, if some crankshafts don’t need a sludge trap, then no crankshaft needs a sludge trap.

Click to expand...

I think that’s a super valid point!

The way I see it, the sludge trap is a throw back to a bygone age, an age when oil had no detergent in it and motorcycles (at least those produced at Meriden) had no meaningful filter in the system.

With these two factors present, the sludge trap is an excellent, in fact, rather ingenious idea. Without them, I think the sludge trap is a redundant relic.

Japanese centrifugal sludge traps, outboard of the main bearing, are even more ingenious.

You can fit one outside the engine.

kommando said:

You can fit one outside the engine.

Centrifuges (PPC) – Glacier Industrial Products

glacierindustrial.com

Click to expand...

If you’ve got oil pressure to spare.

I believe all the T140 crank breakages I have heard of happened on the drive side. If recollection serves me correctly the sludge trap plug is on the opposite side. If I’m correct, not sure what working on the right side of the crank does to strengthen the left side. Plus, there is the unpredictable effect of welding and localized heating.

Because this is a relatively common problem in high rpm, high hp, high compression T140s, I put a steel billet Nourish crank in my race bike in 1996. I raced it 21 more years with no problem.
And, are street T140s commonly breaking their cranks? I hadn’t heard that.

Interesting. I agree the PTO are is a more logical break point. But cracks through the sludge trap is what I saw most of. Maybe different stresses from different type of tune, ie torque stress vs rpm stress?

As to street bikes ‘commonly’ breaking cranks I think not. But even if they have a 99.9% ok rate, it’s not much help if you’re Mr .01% !

I have a slow project on the go which is a 750 Morgo lump which will have Spitfire cams, lightweight (JS Motorsport) Carrillo rods, and billet ‘squish’ MAP pistons. This will run best in the 5-7k rev range. And I want it to be safe doing so.

I‘ve run several Noursih cranks and love ‘em. Sadly no longer available. Even if they were, one wouldn’t suit this build as it’d be out of budget, and I want to keep the ‘68 spec lightweight crank.

Let’s save the light vs heavy crank for another thread. I like both. Different horses for different courses!

BTW, there would be zero localised heat from welding as I would have it laser welded.

But anyway, hopefully you can now see the logic, if there’s a low cost zero down side way to strengthen the crank, then why not. Even if it’s for placebo effect !