Getting the right info to order race pistons

Crank, rods, sealing, pistons, block, flywheel etc
Locked
Guy Croft
Site Admin
Posts: 5003
Joined: Sun Jun 18, 2006 9:31 am
Location: Lincoln, UK
Contact:

Getting the right info to order race pistons

Post by Guy Croft » Fri Jun 15, 2012 11:01 am

Many folk who contact me are stunned to hear that this_or_that piston for engine A or B is not available straight off the shelf. When I explain that - in view of the cost of the parts - it is unwise to stock a standard variant the response usually remains utter disbelief and they then continue to search the internet for that 'instant solution'.

Here I will show some of the dimensional and other key features that need to be determined to ensure that when the pistons arrive they do 'what it says on the box'.
Attachments
JC_measuring deck ht for piston order.JPG
1. Measure the finished deck height of the crankcase
JC_measuring deck ht for piston order.JPG (139.98 KiB) Viewed 4089 times
IMG_5538.JPG
2. time up your cams and set the valve clearances and measure the valve lift at TDC.
IMG_5538.JPG (113.24 KiB) Viewed 4089 times
JC_buretting head for piston order.JPG
3. 'cc' (burette) the had with valves and seats all finished and the head refaced.
JC_buretting head for piston order.JPG (116.57 KiB) Viewed 4089 times
JC_rods & cams (1).JPG
4. Measure the center-center (c-c) length of the rods
JC_rods & cams (1).JPG (50.18 KiB) Viewed 4089 times
Block side race-grade head gasket.jpg
5. Measure the thickness of the substrate and the fire-ring diameter of the intended head gasket. The fire ring will compress - the substrate won't to any great extent.
Block side race-grade head gasket.jpg (59.49 KiB) Viewed 4089 times
CR_JC 2 liter StIII.GIF
put that information into a calculator like this one I use. The CR is a preset and with the other info put in it tells me the dome volume and piston compresssion height.
CR_JC 2 liter StIII.GIF (24.7 KiB) Viewed 4089 times
Alfa 2 liter scheme.JPG
cad allows me to 'model' the dome and VRs for the application. I have to allow for the fact that the valves will be closer to the piston some 18 deg before TDC (ex) and after (inlet) usually by some 1mm or so depending on the cam profile. Closest proximity is never at TDC and people are often surprised by this and the fact that valve peak-lift is not a factor in piston design. I can put the compression height (from crown to pin center) essentially anywhere I like..
Alfa 2 liter scheme.JPG (39.7 KiB) Viewed 4089 times
GC Alfa TC 2 liter race pistons.JPG
and here som GC.CP pistons, in this case for an early Alfa Spider 2 liter Twincam 8V
GC Alfa TC 2 liter race pistons.JPG (67.81 KiB) Viewed 4088 times
Guy Croft, owner

Locked

Who is online

Users browsing this forum: No registered users and 1 guest