GTS Oilreturn

[jerry atric]

What's the consensus on what a decent oil return rate should be, please? my new GTS drips about three times every 2 seconds. A previous one I had, gave a constant high-speed drip. Does the membership think my pump is doing enough?

[RICHARD YAMANE]

The scavenge side just needs to pump a bit more than the pressure side to prevent wet sumping. The pressure side really being a gravity feed is going to be the determining factor. 

Rick Yamane
Importer of Vape/Powerdynamo ignition systems and Polisher of bikes at Motion Pro

On 10/29/2025 12:01 PM PDT jerry atric <baconsl...@gmail.com> wrote:

 

 

What's the consensus on what a decent oil return rate should be, please? my new GTS drips about three times every 2 seconds. A previous one I had, gave a constant high-speed drip. Does the membership think my pump is doing enough?

 

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[jerry atric]

Thanks for the reply, Rick. It doesn't wet sump or smoke when running but I'm worried that the feed is enough. I dont know of any way to check other than watching the return.😳

[Jerome Kimberlin]

Inside the oil pump, check the end clearance of the gears.   Much more than just adequate for turning without binding will lower the oil delivery volume.  The gears are steel and don't wear but the pump casing where the gears spin can wear.  End clearance can be adjusted somewhat by  remachining the fit of the pump parts.

JerryK

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[Andrew Nahum]

Personally I would be happy with that flow rate you describe. It would be enough to convince  me that oil is getting round. It’s a roller bearing engine, after all.  Not  a pressure-fed plain bearing engine. 

Don’t know where you live but few of us need sustained high throttle openings any more so old engines generally have an easier life on the kind of roads we prefer to ride on.   I don’t think there is any other way to check.  The delivery side pressure is probably in the region of 5 psi.   Hardly worth measuring.  

On 30 Oct 2025, at 20:36, jerry atric <baconsl...@gmail.com> wrote:

Thanks for the reply, Rick. It doesn't wet sump or smoke when running but I'm worried that the feed is enough. I dont know of any way to check other than watching the return.😳

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[pouma1954]

Pressure is virtually inexistant in a roller bearing engine. One must think in terms of flow with heat transfer to take into account   not only lubrification.

Paul

Envoyé depuis mon appareil Galaxy

-------- Message d'origine --------

De : Andrew Nahum <andrew...@gmail.com>

Date : 30/10/2025 22:03 (GMT+01:00)

À : guzzi-...@googlegroups.com

Cc : Singles Guzzi <guzzi-...@googlegroups.com>

Objet : Re: [guzzi-singles] GTS Oilreturn

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[Patrick Hayes]

On 10/30/25 13:52, 'Jerome Kimberlin' via Guzzi Singles wrote:
> nside the oil pump, check the end clearance of the gears.   Much more
> than just adequate for turning without binding will lower the oil
> delivery volume.  The gears are steel and don't wear but the pump casing
> where the gears spin can wear.  End clearance can be adjusted somewhat
> by  remachining the fit of the pump parts.
>

I once had a broken gasket for the large outside cap of the oil pump. I
fabricated a replacement ring gasket but didn't worry about thickness of
material. My oil flow went almost to zero! Turns out that the cap
gasket is also a control for the end play of gears against the cover
plug. I made a thinner gasket same as the original and all was restored.

Patrick Hayes
Fremont CA

[Patrick Hayes]

On 10/30/25 13:36, jerry atric wrote:
> I dont know of any way to check other than watching the return.

I once tested a pump. Removed from the bike. Set up a short rubber
hose on the pump intake side and sat the pump in a dish of oil. Ran the
pump shaft with an electric drill and watched oil shoot out through the
crank discharge tube. It was a visual test, but not a flow measurement.
Sprayed pretty good and regular.

Patrick Hayes
Fremont CA

[hicter...@scarlet.be]

The pump is actually a double pump: the gear pump sends oil to the crankshaft. 

The vane pump  in an eccentric , on the plug side, returns the oil to the reservoir .

If the return flow is low, either the seal is damaged, or the eccentric and  vane are worn , or the plug is worn.

Claude. 

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[hicter...@scarlet.be]

The user manual explains that oil is not only used for lubrication, but also for cooling the engine. 

The pump is designed to deliver 60 liters per minute (I assume at maximum speed of around 4000 rpm, not at idle speed!).

There is no mention of possible pump wear or minimum flow rate!

[jerry atric]

Many thanks for the informative answers, chaps. I have a spare pump which I will experiment on and maybe swap them over. But you have reassured me. After  25 years of riding a Scott, one can't help being a little paranoid!

[RICHARD YAMANE]

Aren't Scotts two-stroke?

Rick Yamane
Importer of Vape/Powerdynamo ignition systems and Polisher of bikes at Motion Pro

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[Dave Knaack]

As far as I know yes, I suspect there’s always concern of a two stroke going tight in the bore. We race a 6cyl 2 stroke in a car, it happens! 

Sent from my iPhone

On Oct 31, 2025, at 8:19 AM, 'RICHARD YAMANE' via Guzzi Singles <guzzi-...@googlegroups.com> wrote:



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[RICHARD YAMANE]

For some reason I thought the feed was gravity. Maybe the simplicity of the oil only going directly to the crank has me confused. 

Rick Yamane
Importer of Vape/Powerdynamo ignition systems and Polisher of bikes at Motion Pro

[RICHARD YAMANE]

But they are pumpless. 
With the Budfab LSR project we seized many topends but never put a rod through the case.
What engine do you run in the car? A friend used to race an ex-Fiat PBS in DSR running a Suzuki GT750.

Rick Yamane
Importer of Vape/Powerdynamo ignition systems and Polisher of bikes at Motion Pro

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[Dave Knaack]

We build our own engine based on a kohler engine. Kohler is our biggest sponsor.  Both 4 and 6cyl opposed 2strokes.  We race in the prototype class with scca  we won the national championship race this year 

Sent from my iPhone

On Oct 31, 2025, at 9:15 AM, 'RICHARD YAMANE' via Guzzi Singles <guzzi-...@googlegroups.com> wrote:



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[Rick Yamane]

Congrats! I’ll have to check it out.
It’s been a long time but I think we still hold 3 world records. Our main goal was the 50cc. We used an Aprilia engine with Metrakit topends. John would usually have 6 or so kits in the truck leaving for Bonneville. We got good at changing them. LOL!
We also ran Honda CR80 for the 100cc and CR125 for the 125cc classes.

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[jerry atric]

The Scott engine is lubricated via a Pilgrim pump which was designed for 4 stroke engines so not the best thing for a. 2 stroke. Scotts are capricious bikes; beautiful when they are in a good mood but if they sulk (and they really seem to) they can be awful.

[Andrew Nahum]

The problem with the Pilgrim oil pump in the Scott is that it is running at crankshaft speed - not at half-time timing gear speed as generally in four-strokes.  So you have to screw the regulators down a long way to nearly closed. So they are vulnerable to natural variability and debris. I’ve had a couple of Scotts and they are great fun.  But even so, if it wants to tighten up and seize however much oil you put through them won’t help. You have to get the piston clearances spot on all the way down the piston from top land to skirt. (Several dimensions).  I used the ones advised by Roger Moss, great engineer and Scott racer and finally got the bike to haul. It seems at first sight such a simple engine but really it’s very demanding and has to be put together extremely precisely.  

On 31 Oct 2025, at 20:28, jerry atric <baconsl...@gmail.com> wrote:

The Scott engine is lubricated via a Pilgrim pump which was designed for 4 stroke engines so not the best thing for a. 2 stroke. Scotts are capricious bikes; beautiful when they are in a good mood but if they sulk (and they really seem to) they can be awful.

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[RICHARD YAMANE]

Almost smokes as much as my GTV. (When cold)

Rick Yamane
Importer of Vape/Powerdynamo ignition systems and Polisher of bikes at Motion Pro

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[Andrew Nahum]

It was when I collected the bike and found the motor tightening when asked to pull up hill at 50 MPH.  Sadly between them the Po - the rebuilder - and the cylinder bore outfit had, between them, got it wrong.  This is me screwing open the Pilgrim feeds to try and get home!

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[jerry atric]

Were going off at a tangent here but running synthetic oil made it much more socially acceptable whereas a friend of mine runs his on castor. The smell is gorgeous but you can't see anything behind him for the clouds of smoke😂

[RICHARD YAMANE]

Oh no! An oil thread!

Castor and race gas! It’s two of the greatest aromas ever. The best place for them to come together is a road race course. It’s the reward for being a backmarker. Lol!

Rick Yamane
Importer of Vape/Powerdynamo ignition systems and Polisher of bikes at Motion Pro

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[Mac Dennis]

I rode with a guy who put a spoon full of castor oil in the gas tank of his Indian. The smell was

mesmerizing to say the least.

Mac

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[RICHARD YAMANE]

I used to add some premix to my lawnmower. It doesn’t take much. Sure made mowing more fun.

Rick Yamane
Importer of Vape/Powerdynamo ignition systems and Polisher of bikes at Motion Pro

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[jerry atric]

I still have a dribble of Castrol R in a pint tin (that dates it!) from the good old days; all my mates used to add a drop for the smell. Aaaahh.

[Turboguzzi]

Castrol oil is cool until you have to remove old deposits and stains from parts....

[RICHARD YAMANE]

Castor is a vegatable oil. It laughs at most solvents but is easily cleaned up with dish soaps.
I ran Oilzall or Maxima 971 for around 25 years in all of my 2T dirt bikes. Never had one engine failure. You do need to take precautions with possible separation issues. 

Rick Yamane
Importer of Vape/Powerdynamo ignition systems and Polisher of bikes at Motion Pro

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[Andrew Nahum]

I don't know if it's the change to modern gasoline, or whether the castor oil formulation has, but I did a test with some mix in a glass jar, and the oil did not separate out over a week. The oil was Castrol R, formulated for motor sport. Pump gasoline 95 octane.  I wanted to use it because I'd come to feel that modern two-stroke oil was too thin to give my Guzzino adequate crankcase compression - it started to lose power at low revs.  I'm using 50/50 modern synthetic two-stroke oil and Castrol R now and it seems to slog better.  I should rebuild it with new seals I guess, although one side of the crank appears to have no seal and seems to rely on the fit of the long bronze main bearing bush. Andrew in UK.

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[jerry atric]

I'm told by my Castor-running Scott friend, that modern castor oil does not suffer from the drawbacks of the original stuff and you can leave an engine sitting, these days. Don't quote me though.