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post #1 of 99 (permalink) Old 03-29-2012, 07:32 PM Thread Starter
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Pressure-side oil filter (T140)

Anyone out there have any experience with a Kirby Rowbotham oil filter conversion? This system modifies the timing cover oil galleries so that oil under pressure from the pump runs to a remote filter (typically fitted to the oil-bearing frame tube under the swinging arm), then back to the timing cover where the oil pressure warning light switch used to be. Oil reaches the engine in the normal way, by gravity via the standard tubing from the tank to the oil pipe block fitted to the crankcase and thence into the pump. This means all oil entering the crank and exhaust tappets has passed (via several feet of additional tubing) through a proper car-type paper element filter, under pressure from the feed-side of the pump.

The theory seems great to me (I've just bought one of these kits, but haven't yet fitted it). But in all the numerous posts/topics/threads on the subject of lubrication I have not yet seen any reference to this type of system: most aftermarket oil filters either go on the return line, or at the bottom of the frame-tank.

So, what are your thoughts - and preferably, your own experiences?
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post #2 of 99 (permalink) Old 03-29-2012, 07:59 PM
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I researched this issue and decided the return line filter is superior as it catches the oil at it's hottest, dirtiest condition straight from the crancase and filters all the bad stuff out before it gets pumped back to the oil tank and dumps sludge in there.

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post #3 of 99 (permalink) Old 03-29-2012, 08:41 PM
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I've not heard of that particular system. I must admit it sounds more like a Benny Hill or Monty Pyton character.

Not trying to start another oil filter thread, but this particular design adds a new twist. Putting the filter on the pressure side of the pump is a better idea than putting it on the suction side. But, I'm not sure I would modify the oil supply side of the lube system, which this appears to do. Personally, after reading all the pros and cons discussed here in the past, I agree with OCR and prefer the return side of the scavenging pump for the filter. It makes it a bypass system versus a full flow system and hence, at least in my humble, partially informed opinion, present less risk of oil starvation to the engine.

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post #4 of 99 (permalink) Old 03-29-2012, 08:54 PM
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Neither filter is actually on the suction side of the pump.They are both after the pump.and pressurised by the pump.
No doubt the feed-side filter will work OK,but it seems unneccesarily complicated.

If you only put clean oil into the tank,only clean oil can be pumped to the engine.If it gets dirty when it passes through the engine,the return filter will clean that out and return clean oil to the tank.
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post #5 of 99 (permalink) Old 03-29-2012, 09:04 PM
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I looked at this system when I put in my filter last year. I was turned off when I found out I would have to modify the timing cover. Went with a Tri-Cor instead. Simpler.
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post #6 of 99 (permalink) Old 03-29-2012, 09:24 PM
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Originally Posted by Mr.Pete
If you only put clean oil into the tank,
Hi Mr. Pete,
Clear, concise and correct of course,
Age and mis-adventures could spoil that concept quickly in service and use.
For the oil in frame; 'Charlies' filter anyone?
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post #7 of 99 (permalink) Old 03-30-2012, 04:56 AM
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Looks a lovely system actually but probably not for the purists.

close engine by drfene, on Flickr

Last edited by Dr Fene; 03-30-2012 at 04:59 AM.
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post #8 of 99 (permalink) Old 03-30-2012, 08:40 AM
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I've run a Charlie's filter for years with no problems but have a Norton type to replace it with .. one day. People have said that it's a bit safer to have the cartridge filter after the pump compared to the BSA in tank one.

Personally, I change the OIl probably more often than I need, and I wouldn't want to mod my system for the Kirby one, although he's well respected in engineering.
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post #9 of 99 (permalink) Old 03-30-2012, 03:48 PM Thread Starter
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Thanks for posting Kirby's link Dr Fene, I'd have done so myself if I knew how! Kirby is a very nice bloke who really does know his stuff when it comes to Triumph twins - not a Monty Python or Benny Hill character at all!

For many years I've been convinced that poor lubrication and, in particular, poor oil filtration are the main causes of premature wear and failur in British bike engines. It seems to stand to reason, the lubricant that's keeping metal from metal must be free of any abrasive particles or it'll act as a grinding paste. Not only that, but the particles will clog the oilways and the sludge trap, which can lead to complete starvation to the big ends. Look at any Japanes 4 stroke: they have proper, full-flow paper filters that stop even very small particles. And these Jap engines last a lot longer without major work than their British counterparts. If the only way to assist engine longevity in Brit bikes is to change the oil every 1000 miles, well that's just ridiculous, as well as very expensive. And it just shouldn't be necessary: oil lasts much longer than that if it isn't polluted with rubbish that should have been filtered out.

As far as I can tell, the Kirby Rowbotham conversion is a tried and proven ststem. I know someone who has had this conversion on their T140 for nearly 15 years, no problems, and cleaner oil. It makes sense to me, filtering the oil not only under pressure but in the line between the pump and all engine components. Any crap entering from the tank goes through the pump and straight into the filter: after that, if the filter's doing its job, only clean oil enters the crank.

The only drawbacks I can see are the fact that this system has several more joints and quite a bit more tubing, all of which could potentially lead to leakage and oil feed / oil pressure loss, if any joints or sections of tubing failed. Having said that, I don't see why the likelihoof of failure should be any higher than with the standard setup, as long as all pipes are carefully routed and shrouded from chafing, and as long as all joints are properly made.

I hope I'm right because this is what I'm doing on my TR7. Am I really the only person on this forum to be using this system?

Last edited by JohnA; 03-31-2012 at 07:14 AM. Reason: Got name worng 1st time!
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post #10 of 99 (permalink) Old 03-30-2012, 06:06 PM
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I had not even heard of it till now. It is interesting. Another advantage i think is that the oil gets a little cooling on its way to the engine. That can't hurt. The plumbing looks to be somewhat out of the way visually. Sure would like to see what is done on the inside of the cover.


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