MUSINGS ON RACING DUCATI AND LAVERDA TWINS




I wrote this in 1995 when someone asked for some tips based on my experiences racing a GT750 Ducati and my SF2RR Laverda 750.

All engine and chassis modifications mentioned can be handled by:

Craig has been doing my heads and cranks for the last 15 years, and taught me frame design and construction. I can't recommend him highly enough.

CHASSIS:

Stock frames are very heavy, approximately 60# including swing arm. The frame and swing arm I built for my SF2RR is about 25#. Less weight is equivalent to more horsepower, as well as providing better stopping and handling. A properly designed frame will also result in an increase in stiffness, and allow weight distribution and steering geometry to be optimized.

Low profile 18"-70 series Avon tires have a diameter that is about the same as a 17" tire. Watch out for ground clearance when making a change to a shorter tire. Avoid tires that are oversize for the rims. I run a 130 x 18 on a 3" rim, and it works quite nicely. The standard 2.15" rear rims should work best with 120 width tires.

The Laverda twin will drag on the bottom of the shift box and the dome nut on the primary chain adjuster bolt. If I can shorten the selector spindle I will be able to narrow the shifter box about .25 - .5 inches in addition to beveling the bottom edge (before the tarmac does it for me).

The L-twin Ducati motor makes the bike tail heavy. The SF2 is better, but could stand to have more weight on the front end as well. Moving the seat and pegs forward and using clipons with a lot of offset helps this. Unfortunately using triple clamps with more offset to reduce the trail doesn't help the weight distribution since it moves the front wheel away from the engine.

I put a set of big-twin Guzzi clamps bored out to 38mm on my 650 Alazurra - this was a fairly straight forward swap as these things go. At 65mm the Guzzi clamps have more offset than the Ducati (I think the SF2 clamps have the same offset, but may be slightly different on width) but you will need to make a new steering stem since Ducati uses a 1mm oversize ID steering head bearing. Consider changing to a standard Timken bearing. What the Ducati really needs is to put more offset in the clamps and then move the steering head back and make it steeper to reduce the rake. Consider dropping the clamps on the forks until the fender/sliders just clear at full bump and using longer rear dampers to help steepen the steering geometry. The Guzzi clamps are 195mm wide on center. I built some triple clamps for my SF2RR out of steel tube and sheet. This technique puts the metal where it needs to be for a light and strong structure. It also reduces material costs significantly when compared to billet aluminum.

Extend the taper on the fork damper rod bottoming cone so that it extends over 70 - 90% of the length of the cone. This makes the bottoming less abrupt and allows a bit more movement before hydraulic lock sets in. Progressive Suspension can supply a lighter fork spring (I think it is for a Sportster) since the Marzocchi springs are usually on the stiff side. Make sure the forks have axle pinch bolts on both sides - it only needs a drill and hacksaw to add one to an undrilled fork leg.

Don't make the mistake of using overly stiff springs at either end - you want the tires to follow the bumps, not skip over them. Keep the spring rate down low enough to use all the travel, then jack up the preload to increase the ride height so that the suspension is compressed about 1/3 with the rider aboard. You need to have some downward movement available in the suspension so that the wheels can move down into dips in the pavement.

The Ducati drum rear brake is reasonably light, but the SF2 brake isn't. A lot of drilling/milling can be done on the Ducati hub, cush drive and backing plate to remove a significant amount of extra weight. This can be used on the SF2 to save weight over the stock 2ls rear drum. The SF2 chainline is wider than that on the Ducati, and the sprocket will need to be spaced over to the right to line up with the countershaft sprocket. Consider using an alloy rear sprocket, and changing to 520 chain instead of 530. An alloy rear rim and spoke set for a KZ900/1000 Kawasaki was a perfect match for the Ducati wheel. The SFC magnesium disc hubs have a reputation for cracking. A Kosman billet rear hub is very nice but expensive. Some people have used Suzuki disc-brake/wire wheel hubs on an SF2 - they are cheaper but heavier. I used Astralite wheels when running the SF2 in BOTT, there was plenty of clearance between the chain and tire with a 3.5" x 18 rim size.

Converting to a hollow 25mm axle on the front will save weight and greatly increase the fork's resistance to flex.

ENGINE:

An electronic tachometer eliminates a possible oil leak at the tach drive. Ducati has been known for engine pressure forcing oil up the cable into the tach. I can supply Scitsu tachs which can run either on an internal battery or from the bikes battery.

A well-designed two into one exhaust is better than individual pipes on both bikes, though it is more difficult to make as a high pipe. I've really become a believer in high pipes for road racers. While running the SF2 on the dyno we pulled the tailpipe/megaphone off and installed two individual megaphones. This caused massive flat spots and a 20 bhp drop. The SFC 2-1 system looks to be a not very good design compared to what Craig designed for my SF2. Hang a stack of SuperTrapp discs on the end of the megaphone to quiet things down (a bit). 24 4" discs did not affect the power numbers on the SF2, and seemed to provide enough back pressure to smooth some minor rough spots in the power band.

I had good luck (and still do) with Kendall oils. With the oil being shared with the transmission/clutch it should be changed so frequently in order to remove metal/clutch fibers that that oil never has a chance to wear out.

Eliminate the pumps from the Dell'Orto carbs. They are of no value on the track (and don't seem to help on the street either) and they waste gas and make the carb pull stiffer.

40mm carbs work fine on either engine. A problem with the Laverda frame is that it forces the carbs up against the engine with a short air straightener (velocity stack). My SF2 made more horsepower with an 11" intake tract (measured from the cylinder head/manifold joint to the back of the air straightener). I also switched to Japanese-style rubber inlet manifolds for heat and vibration isolation.

The plastic air straighteners that come on Dell'Orto carbs are junk and don't work when tested on a flow bench. Use the aluminum Malossi items instead, as they actually increase flow.

I can supply modern valve springs with titanium retainers for both bikes.

I believe the later triples utilized two single row primary chains in place of the triplex chain. This would be a good idea for a twin since the two individual chains will tolerate more sprocket misalignment, are just as strong as the triplex chain and should be lighter and cheaper as well. I spoke to a fellow who experienced a broken primary chain on his SFC at high speed, and he didn't recommend the experience.

The SFC oil pump increases volume and is a bolt on item for the SF2. The SFC plastic chain tension wheel uses a needle bearing instead of a bushing - I don't think this will be enough of an improvement to require changing a good condition SF2 component.

My SF2 doesn't seem to need an oil cooler. I have considered routing the oil out of the case as on the oil cooler equipped SFC and running an external oil filter to supplement the basically useless stock item. Since roller bearing engines have very low oil pump pressure I would use an Oberg filter screen with an appropriately sized filter aperture. A regular automotive paper filter would probably be much to restrictive.

The Laverda crankpins are fed from the main bearings, with oil collected by sheet metal slinger plates (like many two strokes). These plates on the SF2 have a larger OD than the crankpin hole, and act as a centrifugal filter for the oil. When we lightened the crank on my SF2 we discovered that the slinger was silted up almost to the point of blocking the crankpin oil hole. Cleaning the slinger plates out with some bent wire and solvent is highly recommended.

I had the stock rods magnafluxed and shot-peened. As long as reasonable rpm are used there should be no need for Carillo rods. The SFC rod big-ends are narrower than the SF2, and won't interchange. Carillo rods would probably be of higher quality and cheaper anyway (and therefore a good idea on the SFC as well).

Approximately 8# was removed from my SF2 crank. The SFC crank is lighter than a stock SF2 item, but I don't know by how much. The starter sprag clutch/dynamo pulley is a pretty heavy lump and should be removed. I have not been able to find an oil seal that will fit in the crankcase and on the crank. The stock unit has an 80mm od with a 45mm id, and the crank seal has a 25mm id. I think that one of the easier ways to deal with this would be to make an 80mm aluminum seal carrier, and fit a small od 25mm id seal into it. This would need to be closely tolerenced on the od so the crankcase is still able to pull up properly, while avoiding the seal holder being too loose of a fit. It might be worthwhile to groove the outside of the seal holder and fit a small o-ring that would crush into the groove to ensure a good oil seal. Some sort of crash guard for the end of the crank, whether the stock cover or something else would be nice. If you wanted to, a tophat shaped aluminum cover could be made and then be attached with screws (be sure to seal them) to the aluminum seal holder. Then again, if you actually went down this might yank the sealholder out of the case, so a guard attached to the case would probably be better. On my bike Craig made an aluminum part that fits on the crank and matches up to the stock oil seal.

I've been using the stock SF2 clutch and transmission, and see no need at present for the close ratio gear set. The clutch cush rubbers do eventually pack down and cause some slop, but they are fairly easy to replace. I am considering making a longer clutch throwout lever to make for an easier pull at the handlebar. It is made from a flat sheet of steel, and can be duplicated with a hacksaw and file.

Every engine must be tested on a dyno. I have run two engines that I thought were doing OK on the track on a dyno, and with carburetion and ignition tuning picked up 50% bhp! Granted, I'm no ace seat of the pants tuner, but wouldn't even a 20% improvement be worth the effort and money?

IGNITION TIMING:

The stock full advance ignition timing is 38 degrees on the Ducati and 40 degrees for the SF2. You are recommended to use an initial timing on a stock engine that is 3 or 4 degrees retarded from the stock position. With the RITA ignition you will get a spark every time one is supposed to occur. This is not the case with many points ignitions! Since you are experiencing a more regular combustion the engine may run slightly hotter. Therefore you should start with the timing slightly retarded and only advance it if testing indicates it is needed.

Heavy ignition advance is a sign of inefficient combustion. If your bike has had the squish band between the piston and cylinder head set properly (my SF2 race engine with SFC pistons required .080" machined from the cylinder base to do this (but it turns out this was because I was sold SFC Electronica pistons instead of the earlier taller pistons - thanks to Marnix for sorting me out here) you will be getting a great increase in turbulence in the combustion chamber which reduces the need for ignition advance. Do not fall prey to the common fallacy of over-advancing the ignition timing in the mistaken belief that it will give you more power. It is more likely to give you an increase in the number of holes in the top of your pistons. Even my fairly stock (squish bands, pipe, port cleanup, stock carbs) 650 Cagiva requires less advance than stock specifications.

SEVERAL WORDS ABOUT COIL SELECTION WITH A RITA IGNITION

The RITA ignition will work with coils that have a total resistance in the 3 to 4 ohm range. Measure the resistance of the coil(s) you hope to use before installation. The wiring diagram supplied would be used with two single-lead coils wired in parallel with each coil having a primary resistance in the 3-4 ohm range. If you wish you can use two single-lead coils with 1.5 - 2 ohm primary resistance wired in series. Another option is to use a single dual-lead coil with 3 to 4 ohms primary resistance. In the last two instances the diodes can be eliminated from the system; they are only needed with two coils wired in parallel.

Two coils wired in parallel will have twice the current draw as the other coil arrangements, presuming that all the options have an equal total primary resistance. Also, a three ohm system will have a higher current draw than a 4 ohm system. If your generator is not very effective you should consider the coils in series/dual lead coil and/or a 4 ohm system to reduce current draw.

For dual plug application just substitute dual lead coils for the single lead coils of the same primary resistance.


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© 1996-2005 Michael Moore, last update for this page 01 June 2005

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