Skim A Block
#1
Posted 18 August 2017 - 02:39 PM
I'll probably fit low compression pistons (21251) to compensate for too high a compression ratio.
#2
Posted 18 August 2017 - 03:16 PM
Ac
#3
Posted 18 August 2017 - 04:25 PM
#4
Posted 18 August 2017 - 06:29 PM
Ac
#5
Posted 18 August 2017 - 06:42 PM
Think I may have to look at different pistons then. Ones with a bit of meat on the top but still low CR. I think the chambers are as factory so a little grinding would help with the CR as well. Any suggestions of piston? My other 1293 uses 21253 but think the CR would be too high in this case.You will likely need to use a piston that can stand a little removing from the crown while maintaining a reasonable dish volume. You might also have to consider opening the chambers out in the head to maintain a decent sane compression ratio.
Ac
#6
Posted 18 August 2017 - 06:53 PM
Think I may have to look at different pistons then. Ones with a bit of meat on the top but still low CR. I think the chambers are as factory so a little grinding would help with the CR as well. Any suggestions of piston? My other 1293 uses 21253 but think the CR would be too high in this case.You will likely need to use a piston that can stand a little removing from the crown while maintaining a reasonable dish volume. You might also have to consider opening the chambers out in the head to maintain a decent sane compression ratio.
Ac
Machine the 21253 pistons to give the correct compression ratio along with a little work on the head, or, look at the C-STN100.
#7
Posted 18 August 2017 - 08:57 PM
I've use countless sets of these;-
http://minisport.com...et-hypatec-1330
while are a "9.7:1" CR Piston, they can have loads machined out of the crown quite safely, I'll post up a pic later.
They also use more common imperial rings, so you have a much wider range of choice of brands and types of rings available. The AE Pistons I have to say, I went off years ago as the rings are odd-ball metric types, which only AE have and the design / manufacture of their rings isn't remotely what it was. I also found their pistons (last time I had some) varied a lot in manufacture.
#8
Posted 18 August 2017 - 09:22 PM
You may well be OK with the famous 21253. It is unlikely the block will need more than about 0.030" skimmed from it. It may be that the pistons would have been sitting around 10 to 15 thou down the bores, so you would only need to take 15 thou to 20 thou from the piston top, which is entirely OK.
The standard head would still need skimming to get a reasonable CR of, say, 10:1, especially after a bit of chamber improvement, so you are very unlikely to have any problem.
It is unlikely you have any engineering problem here. Even if the piston had a lot machined from it and the chambers were already small due to earlier skimming, it is easy to increase the capacity of the chambers by 2 or 3 thou each.
#9
Posted 19 August 2017 - 11:23 AM
#10
Posted 19 August 2017 - 11:41 AM
Ac
#11
Posted 19 August 2017 - 11:58 AM
Thanks, I'm in Cardiff and currently go use Dale at Pogsons but if the weather's nice, you never know.If you are near Salisbury, I can takes look, and skim it for you if needed.
Ac
Edited by whistler, 19 August 2017 - 11:58 AM.
#12
Posted 19 August 2017 - 01:27 PM
Ac
Edited by ACDodd, 19 August 2017 - 01:29 PM.
0 user(s) are reading this topic
0 members, 0 guests, 0 anonymous users