Sump Spacer

[GuzziNZ]

A couple of questions about installing a sump spacer on my 850T.
Do I need to extend the drain pipe inside the engine coming from the breather box. For example, should it come out under the oil level?
And since the T had no filter the oil volume was 3.5 liters.
Having now modified it to run a filter I am guessing it should be 3 liters as per a T3 etc?

[Dukedesmo]

Are you intending to fill to the same level? if so then the breather pipe will sit at the same point so no change.

[moto]

Back in the heyday of sump spacers the conventional wisdom was to keep using the same amount of oil so that the level below the filler plug would increase. MG Cycle sells or sold appropriate, longer dipsticks. Usually the justification for installing a sump spacer was to reduce churning and windage losses from having the surface of the oil too close to the spinning crank.

For the same reason, some, especially Pete Roper, made and sold windage plates that sat just below the bottom edge of the crankcase proper, above the spacer. At the time, Pete recommended cutting off the return pipe so that it was above the level of the oil. I forget what his reason was, but I accordingly cut mine off when I installed his windage plate and a sump spacer on my T3.

Pete later backed away from his enthusiasm for windage plates on the original series of big blocks. I can't hold his change of opinion against him.

Some have always advocated sump spacers to increase the oil volume on small blocks, but not on big blocks.

Having invested in both a spacer and a windage plate, I suspect that my T3 is no better off than it was. I did have a problem of oil loss through the breather that I thought might be caused by excessive windage, but what fixed that was new pistons and rings.

My feeling is that an original-series big block motor in good shape doesn't really need a sump spacer, and that anyone looking for extra horsepower from adding such stuff is probably dreaming, and probably should be dreaming about a more powerful model instead if more power is wanted.

Just my impressions, more historical observation than sound mechanical insight. I am always happy to learn from my betters. Good luck.

P.S. Talk about excessive windage. My apologies.

[GuzziNZ]

Thanks for the reply. I always believed that the spacer was not there to hold more oil but as you said to help with windage by mover the oil level further away.
I also noticed on the spacer four unused lugs that look perfect for bolting a windage plate too.
Anyway I have the plate so I will throw it on with 3 litres(?) Of oil and  alter the dipstick to suit.
The only benefit maybe in a slightly lower oil temp.

[pehayes]

A slightly contrary opinion.  The sump spacer concept was not intended for increasing oil volume.  The proof is that '98EVs came from the factory with spacer in position and no change the specified oil volume.  The engineering intent for the spacer was to increase the relative volume of air sitting above the oil level.  The volume of air above oil is constantly changing as pistons rise and fall.  Thus, the 'atmospheric pressure' inside the crankcase is rapidly increasing and decreasing.  When that pressure is on the positive side, there is a tendency to push oil mist or oil film past seal lips, o-rings, and gaskets.  Reducing the pressure fluctuation helps keep the oil inside where it belongs.

Many, many moons ago there was a chap producing sump spacers for Ambassador and Eldorado.  I bought one.  (find his ads in very old MGNOC newsletters)  Those engines had an oil pickup and screen dangling from below the crankcase casting and not associated with the sump itself.  His kit not only provided the sump spacer to drop the sump, but also a block spacer required to drop the oil pickup and screen by the same dimension so that you were still pulling oil from the bottom of the sump.  The later engine and sump designs put the pickup and filter as an integral part of the sump casting.  Dropping the sump with a spacer simultaneously dropped the pickup and filter.  The 850-T was intermediate and I'm not certain about its sump  and oil pickup design.

YMMV.

Patrick Hayes
Fremont CA

[Dukedesmo]

Very informative 


Whilst I'll happily admit, I'm no expert on Guzzi engines, I do have some experience with crankcase breathing, oil blow-by etc. from (90 degree V-twin) Ducati engines which can have issues on this front (more so than Guzzis IME), due to the higher revving engines.


FWIW, on my LM2 I installed a windage plate - sandwiched between the base of the block and the external filter sump that I also bought (didn't like having to remove the sump to change the filter).


Whilst the external filter sump is deeper, when filled up to just under the windage plate, it holds around 3L which is, I think around the same as the original? plus, the 200ml or so in the filter.


I needed a new dipstick anyway as my original was a long one in an extension tube for the LM2 fairing.


I like the idea of a bigger air gap between crank and oil but I also like the idea of more oil as it surely must be better for cooling and generally lasting longer due to any particulates/molecular breakdown being more 'diluted'.


I left the oil return/drain as it was as it sits under the oil level, I did modify the breather valve (using a large reed valve) and fit a bigger oil breather box (both from Ducati experience) and have had no issues with blow-by or any oil escaping the breather/catch tank and the bike uses no (noticeable) oil between changes.


I'd need to see conclusive evidence of it being an improvement before cutting off the return pipe above oil level and until then, I'd be making sure it sits in the oil as before so, extending it if required.

[GuzziNZ]

Thanks for the reply Dukedesmo.
I also made a new breather box using a reed valve from a scooter that seems to work great.
As for the oil amount I will be using 3 litres as used in the T3 etc but because of the spacer the oil drain pipe maybe higher than the oil level  so will receive pressure pulses while running. Hence why I asked , should it be lengthened?