Picco P/L EXR 3.5

[Kevin_R_Clark]

Purchased a modified EXR that needed rebuilt. Have all the stock parts for the job. The case has been reworked/relieved near the the bottom of the ports. The backplate appears stock, maybe a little work on the inside done. The old Piston compared to the stock new one. The new one has an eyebrow, the old one has been skirted almost the size of the exhaust port. Also has 4 holes in the skirt the new one does not have. The old Liner is so modified that I am not even going to attempt to copy it. The only thing I want to know about right now is it has been relieved straight down from all the intake ports, to the point it is very thin near the bottom of the ports. The relieve job is pretty rough, groves horizontally. Shouldn`t these be smooth? Ok, I will be doing this by hand and magnifing glass. First the Liner, I filed and approx 60 angle on the bottom keeping a nice clean edge on the bottom. The Boost ports, I notice the one opposite the exhaust already has an angle milled on the bottom. Should I go ahead and do them all? Relieving below the ports, is this worth the time? Do I need to do it if I am not going to change the timming? The Piston, how much skirting needs to be done, what about the 4 holes? Thanx, for your help!

 

[Kevin_R_Clark]

All right so you guys are either real secretive about this or it was just to much/many things to answer. So let me narrow it down a little. Got the old how to books out, and even tried looking thru past Tech notes- didn`t find anything though. Went ahead and beveled the bottom of both the ports and liner. So I will narrow it down to 2 questions, First the relieving below the boost ports. Specifically the ones that run from the bottom of the liner to what I have already done. Is this only necessary on an all out motor or should it be done as a rule of thumb. Second, exhaust port. The how to books say to raise only the middle of the port. Since I have yet to get a degree wheel that will work on these small motors, I would be doing this in the dark so to speak. Is the stock timing just fine or is it normal to raise the port?

 

[Scott Schneider]

:blink: Ok, Let me try and help you. I have owned 4 picco .21's and 2 are the black case tilted Exhaust spigot EXR's. Have tried all the tricks, But damm near stock is best!

The stock EX timing is fine as is transfer timing. All I would do is to sharpen bottom of liner to streamline the flow into transfer/boost port runners, Round out the bottom edge of each transfer window. Deburr all flashing around all ports and with 1500 wet dry lightly bevel all ports on the bore side. Piston you can skirt backside to enhance flow into boost port runners. Other than that I would leave it alone and not get carried away carving it up.

Scott