Monthly Archives: August 2017

Front wheel hub with more commercially available disc brakes

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During the Benelli 350RS period the front hub drew attention: it had the same brake discs as the Guzzi 350/500 models and the hub looked similar to that of the beveltwin SS spoke hubs, just a bit smaller.
I managed to acquire a hub from another Benelli model (250 2C) and machined the bearing housings to fit the (standard) PT bearing size 6004, as the Benelli hub has a smaller axle size. Also a new spacer was machined to fit between the new bearings.

Quite possible the hubs on some Guzzi models are same/similar to the GTL, and when the major distance between the discs are same to that of the GTL, they can be modified to fit the PT front forks with original yokes.
Yes, that does mean that fitting wider fork, from a pantah for example, is possible so fitting pantah wheels, or wheels with larger major distance between the discs, is possible.

Personally, I prefer the GTL/SD/GTV yokes with GTL/Benelli hub as then the spoke wheels are kept and they are less bulky on such a small nimble machine.

Front sprocket(s) SD/GTV

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GTL gearboxes have the tapered end with keyway, and new sprockets for them are as hard to find as new crank bearings.
Until I have found a commercially viable method for alternatives for GTL sprockets, I have diverted efforts into the SD/GTV gearboxes as these have the “regular” 6 spline shaft like the pantah. Again, ploughing through the JT Sprockets catalogue an alternative was found, although it was a 520 chain rather than original 530. The thinner chain is not so much an issue as modern 520 chains are extremely strong, but it does mean sprockets for the GTL have to be modified. SD/GTV wheels have the same sprocket carrier as the pantah/750Paso/Sport 16″ wheels, and those sprockets are still readily available.
the front sprocket was found to be the same as a Yamaha 250 dirtbike, and available in Z12 and Z13, just like the 350 and 500 models. A distance bushing is required to ensure correct chain alignment.

front sprocket 520 (SD/GTV): JTF431.12 (350) and JTF431.13 (500).
rear sprocket 520: JTR491.38 and JTR491.40
rear sprocket 530: JTR1022.38/40/41/47
fitment 520 front sprocket: place the collar to the outside so front sprocket backside is flush with rear sprocket backside.
spacer required for 520 sprocket: 22(+0.2/-0) x 28(±0.2) x 6.7(±0.3) mm
advised: strong belleville spring washer DIN2093 22.4 x 45 x 1.25 with loctite 242/243.

UPDATE:
We are currently in negotiations to get GTL sprockets manufactured in 530 chainsize
(5/8″ x 3/8″) for both 350 and 500 models, z=12 and z=13 respectively.

Desmo shims for the Parallel twin

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Many riders with the desmo head on their PT have come across the need for thicker closing shims. With my 500 head without shims I needed to start from scratch. Having some shims left over from belt drive desmo heads, the valves only needed to have a new groove in the stems roughly 4~5 mm lower than the original to have them instead.
As the 500 head needed new valve seats, larger 600SS/Monster valves were taken and those modified with new grooves, and now desmo adjustment can be done with standard available shims from your local Ducati dealer. Problem solved!

2014-01-25 18.25.57

Oil filter

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These are increasingly difficult to find. When I still had my Benelli 350RS it also needed a new filter, which was the same as the Honda CB350/400/500/550 Fours. But remarkably these looked very similar to the PT filter, with the exception they are not flat on one side. So the easy thing to do was to make a spacer ring to accommodate for the flat part of the original filter. And it works.

While dismantling few GTV engines I noticed the oil filters were identical, and these may well be the next best alternative to the Champion X315 oil filter:
UFI 25.502.00

Main bearings

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Of all the parts used in a parallel twin, these are on the top of the list of hard to find items. Not a single bearing distributor nor manufacturer has these bearings in their standard supply, so the best (economical) decision is to make them yourself.

The design has been slightly adjusted with more lubrication groves in the flange to accommodate the axial load of the crank, and the groove in the inner diameter is now whole as compared to the original. The first test samples were made of Aluminium bronze, which was used as bearing material in heavy gas powered combustion engines for the crankshaft and camshaft and rocker arms, hens the first reason for selecting them.
The did not pass the test, as the crank locked up twice on the dyno once above 4000rpm. The cause was found to be the wrong material, and this was supported by literature on bearing designs and backed by experience from several engine tuners.

IMG_0029

So with more information I set out to find more suitable material and have at this moment put out quotations. While the test specimens are made, a separate engine will be put together with these new bearings and bolted into leftover GTV frame for dyno endurance testing.

Another trial is converting the crankshaft from plain bearings to ball bearings. This is parallel to the above project to manufacture new plain bearings.
Using the same approach as the Pantah, the left side will have the same steel bearing housing as the pantah (and subsequently all modern beltdrive ducs) together with the angular contact bearing (7207). This is because the angled primary drive pushes the crank to the left under accelertion and therefore almost all of its rotating life.
The right side will get a conventional ball bearing to take the radial load and the occasional axial load during engine deceleration.
The crank does need modding to get the oil into the crank (right side) and to both bigend journals. Oil supply will be from the oil gallery where the oil pressure sensor is located.
right side welded up to add material

left side welded up to add material