98 Sei Giorni update

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siatamm
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Joined: Sun Sep 16, 2012 4:22 am

98 Sei Giorni update

Postby siatamm » Mon Feb 03, 2014 8:49 pm

When I started the restoration of this motorcycle I didn't know what I had because the serial number was odd. I thought the motor would be the easiest part, it looked like it had very little cylinder wear, had good compression and all the gears were there, clean oil ect. On that basis I went ahead and restored the rest of the bike and didn't worry about the motor. When I started it up it blew a lot of oil and smoke out the exhaust. I checked for oil level (1.5 kg didn't make sense to me), oil viscosity, blocked lines, ring gaps, valve guides. I tried to get new piston rings but wound up having to buy the whole piston. When I got the piston it was different, flat top instead of domed. No problem, I switched the rings to the old piston honed the bore but also I noticed that I was missing a part where the oil from the pump enters the end of the crankshaft. At this time I tried to figure out the oiling system, no easy task as Gilera changed the system from a spray over the rockers to forced through the rocker shaft. In doing this just to confuse things they left vestiges of the old system in place and didn't bother to change the illustrations in the manuals or sometimes they had a mixture of new and old illustrations. To add confusion it was becoming clear that some things were unique to Sei Giorni and others were only evolutionary changes to all 98's. I made what was my best guess as replicating the missing part (29831 Spingitoio) and tried the motor again but had the same problems. The motor was definitely getting oil, too much. I decided to go ahead and run it to see if the oiling problem would clear up maybe the rings would seat. I suspected this was wishful thinking but I thought it wouldn't hurt. Wrong! After only a few miles it made some bad sounds, lost power and stopped When I took the motor apart (involving making special tools) I found the connecting rod bent and the big end bearing completely reduced to bronze filings. I was amazed that it could have happened so quickly. The piston had hit the head going up and the crankshaft going down and was ruined. The valves were not hit and the head and crank did not seem to be damaged. Earlier I noted that the valves were 124, larger than 98 size. I took the crankshaft apart and found some bits that might have obstructed oil flow but I couldn't be sure. I ordered a new 98 connecting rod and pin from Bob wright and he was also able to find me a Spingitoio. When It came to putting the crank back together I realized the new connecting rod big end was too narrow and the pin was too short. I called Bob Wright and he couldn't explain it. It occurred to me to check the dimensions of the 124 connecting rod and I found that a 98 Sei Giorni apparently used a 124 rod and pin. I ordered the 124 rod and pin and installed them in my crank. The new rod is dimensionally the same size but noticeably heavier than the original rod but balancing is outside of my knowledge, I'm hoping it won't be a problem. During reassembly I tried to fit the Spingitoio into its place in the side cover at the oil pump but it wouldn't fit far enough in to allow the cover to fit. I examined the opening in the side cover and noticed a ridge down in the opening. When I fished around with a little hooked tool I pulled out the missing Spingitoio!! Someone had put it in backwards and behind the spring and the Iniettore (29832). I guess they never tried to ride it after they put it back together.

Now It's almost back together. I'm using the flat top piston that I took the rings off. It will lower the compression a bit. I hope the new heavier rod is not a problem I also hope that the oiling problem is solved. As suggested by Nozem I tried to see if I was getting oil to the rod before I installed the piston and cylinder by turning it over. A good idea but difficult to see because the sides of the rod are recessed into the flywheels on either side. I will have to wait until Spring to start it up, and I'm cautiously optimistic.

I'm still curious about the 98 Sei Giorni engine. Is it really a 1961 as the registro said or is that the date production started? Do the differences simply reflect changes made to all later 98 models?
Serial no. 002-1706 with 4 speed gearbox.

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