Fab Flash 7: Fabrizi 50mm Cylinder Kit (74.6MPH)

[bakaracer]

Does the combustion chamber protrude down from the head? The old ones use to sit inside the cylinder about 1mm. If it does you need to add base gaskets or use a thicker one. Then check squish clearance.

[Red Eft Performance]

So I got some feed back from a customer that is familiar with this kit. He said that you have to either cut the piston or the cases. (I know We already came to that conclusion but he confirms this and is aware of this problem)
He said that this kit loves the malossi crank and "puts smile on face"
I talked to Fabrizi and they said they have never had this problem and that the new kits will have modified piston already.
I would say that our af16 cases are slightly different than the Dio cases.



Keith

[swimmingfree]

nice looking set up what size is the piston ? 50mm ?? why is there not a link to get the top end kit??
swimmingfree

[Wheelman-111]

Greetings:

The 50mm (81.25cc) kit was supplied by RedEftPerformance, so if you need a link, PM him, Free. Last time I read he was sold out.

LMH your points are right-on, of course. The rod length HAS to be the same if the stroke is, which I measured to be true. I was bum-fuddled as to why the piston wouldn't clear and looking for an oddball reason. I guess the Dio case doesn't have the issue while the AF16 does?

Yes, Baka-san the combustion chamber sits a bit proud of the head, but the piston sits about that distance below deck. Somebody link me up to a thread or explain the best squish clearance method please? (Something about solder, but I've never quite understood how you cut the length without crushing the end, a little. Compresson will tell part of the tale, but are you saying high-RPM contact between the crown and head can occur?

If so, Red can you supply a base gasket? All of my 50mms have a Giant Boost Port cutout, and I don't think enough of the paper will be trapped by this cylinder to be safe. I think I also have a 1mm thick head spacer somewhere, but not sure how that'd work with an o-ring gasket. The interface between the cylinder and the spacer won't be gasketed. (Is that even a word?!)

BTW, Fabrizi's assertion makes no sense, unless there's something I don't see. If Fabrizi "never had a problem with this...", then why would they say the new pistons are modified? In any case, I wouldn't mind getting one of the "new" pistons cut by their Craftsmen instead of Wheelman's Rock-and-Stick toolkit. PM me about it?

[Wheelman-111]

Greetings:

I did my own research on Squish Clearance measurement. Here's a Wordy One.
From the folks at Gas Gas
This one's four-stroke from Nallin Racing with tons of Harley racing experience. (Is that an oxymoron?)
Finally one from Hammer Performance. They all say about the same thing. I think I have some flux core solder somewhere, need to measure its thickness.

[Red Eft Performance]

Greetings:
BTW, Fabrizi's assertion makes no sense, unless there's something I don't see. If Fabrizi "never had a problem with this...", then why would they say the new pistons are modified? In any case, I wouldn't mind getting one of the "new" pistons cut by their Craftsmen instead of Wheelman's Rock-and-Stick toolkit. PM me about it?

The reason the new pistons will be modified is because I sent them your photos and told them about the problem so they are going to fix the problem on the next batch coming to me.


They dont have this problem on the Dio.

[Wheelman-111]

Greetings:

In that case, please review the pics of my cutout piston. I used a carpenter's square to scribe a line 4mm from the bottom of the piston skirt, then shaped the cutout to avoid "corners". They probably don't need to remove that much; 3mm is should be enough, but I didn't want to do it twice. I don't like re-using piston pin circlips, but I was careful not to over-compress mine. I gotta say the fit-and-finish of these parts is otherwise extraordinary. I just hope I don't muck it up with the wrong jets or somesuch.

[LMH]

The fun is going to be tuning a cylinder with too small of an exhaust chamber. Your jetting is going to be way different than someone using the correct pipe.
You may or may not run into some serious high rpm problems. The real issue is that this is an 11k rpm cylinder and you'll be using a pipe that is 10-10.5k @72cc. There may not be enough chamber to do a good scavenge which in turn will slow the piston.
Baka probably has some good insight on it. I've never tried to run a 50mm kit with out using a large v8 pipe let alone a racing 50mm.

[Wheelman-111]

Greetings:

No doubt you have a point, LMH. I didn't think the Scorp was all that much better than the PG short on the MHR, although it was a good bit Louder. Between them, I haven't compared sizes but based on the crisper low-end of the PG I suspect the Scorp is a little bigger, albeit probably still not big enough. The trouble is my liver growth rate; I can't afford to lose another lobe until it grows in some more. At that point if Eftie still has a Fabi pipe for sale I may spring for one. For now, I'll see what I can get with the Scorpion installed, if only for break-in.

For the record, the PG short managed a bit north of 10.5K on the Corsa 72 on its 70+ MPH run. We'll eventually see how much spinnage the Scorpion will support with 81.25ccs. That's about 13% more displacement.

[bakaracer]

The pg short and scorp should work fine. They are for 72-90cc setups. The pg has a wider powerband tuning wise than the scorp but the scorp will rev way higher(up to 12.5k) than the pg but you sacrifice the wide powerband. Both should work fine

[Wheelman-111]

Greetings:

I always appreciate your input, Bak. I'll post results once I complete squish measurements, check CR, and choose jets.

[bakaracer]

Also measure the exhaust port opening flange side and see what diameter it is. By the looks it looks to be about 26-27mm

[ped]

Greetings:

I did my own research on Squish Clearance measurement. Here's a Wordy One.
From the folks at Gas Gas
This one's four-stroke from Nallin Racing with tons of Harley racing experience. (Is that an oxymoron?)
Finally one from Hammer Performance. They all say about the same thing. I think I have some flux core solder somewhere, need to measure its thickness.

hi wheelman. do you have a photo of the dome on the head? or did you put it all back together? will u post if you do? thanks.

[Wheelman-111]

Greetings:

Stay tuned to this channel. I recorded the process.

[Wheelman-111]

Greetings:

As planned, a pleasant Wheel-garage evening was enjoyed. First thing was to check my Solder inventory. Despite being worse at soldering than I am at painting and photography, I had 2 sizes! The .97 mm was deemed thick enough.

Solder.97.jpg (177.13 KiB) Viewed 6858 times

next, I tried the cross-legged U method, but decided to remove the head instead.

F7SquishSolder.jpg (205.07 KiB) Viewed 6858 times

next I carefully torqued the head back on and rolled over TDC, noting a very slight resistance.

f7TorqueDown.jpg (148.66 KiB) Viewed 6858 times

removing the solder segments, I examined for flattening and found the fine cast lines on the piston crown were pressed into the solder.

F7SolderCrush.jpg (115.06 KiB) Viewed 6858 times

F7Squish73.jpg (161.65 KiB) Viewed 6858 times

Finally, measured thickness at 0.77 and 0.73. Over 0.6 should be OK, right?

F7Cmprsn145.jpg (146.92 KiB) Viewed 6858 times

Last thing was Compression, which came in at 145 and no higher. I am pleased so far except for my carb issue in Perf. Tech.