Author Topic: another rod question  (Read 4045 times)

0 Members and 1 Guest are viewing this topic.

Offline dropzone

  • Newbie
  • *
  • Posts: 18
  • Karma: 0
    • View Profile
another rod question
« on: June 30, 2009, 12:39:37 am »
I didn't want to hijack another post. I was reading and I Quote dyoung14
"i dont know the sizes but the numbers, but i do know that a 40 ci has a longer rod than the 42, i have a 42 that i put 40 rods on my 42 crank and didnt mill the pistons, i put 40 ci heads on and have plenty of clearence, and it runs like a bat out of  well you get the point" Will this really work putting 40 rods on a 42 and not mill the pistons?  Would I use the 40 pistons or the 42?  Ive read that the pistons need to have .05 milled :confused:







     
 

 

 

Offline Rooster

  • Global Pot Stirrer
  • Highly Mowtivated
  • ****
  • Posts: 8255
  • Karma: 73
  • Gender: Male
  • Winning is always fair!!
    • View Profile
    • Cut Loose Racing
Re: another rod question
« Reply #1 on: June 30, 2009, 02:09:21 am »
Pistons are the same
Bert stole my cookies!!
 I think he used them to bribe Ed into something naughty?

http://www.cutlooseracing.com

Offline dyoung14

  • Newbie
  • *
  • Posts: 23
  • Karma: 0
    • View Profile
Re: another rod question
« Reply #2 on: June 30, 2009, 06:50:44 pm »
put 40 rods in the 42 block use which ever piston it dont matter, the 40 heads have a dish in them were the piston is use 40 heads and you have plenty of clearance and yes the pistons come out of the block but the dont hit nothing!

mmsports

  • Guest
Re: another rod question
« Reply #3 on: July 01, 2009, 08:16:44 pm »
That's all fine and dandy but it probably actually decreases overall power unless you mill the pistons down. On a flathead I generally try to keep the piston in the bore atleast 0.005". To do that you would have to mill off 0.055" which is still safe.  I'm not sure where the failure point is, but if you mill .070" off you might make 2 races before the top caves in.  Just a little food for thought.

Offline dropzone

  • Newbie
  • *
  • Posts: 18
  • Karma: 0
    • View Profile
Re: another rod question
« Reply #4 on: July 02, 2009, 12:41:49 am »
It's not going to be raced. I have a 16 opp in a golfcart and I picked up a 18 complete for 20$ for parts. I'm going to use the rotating assembly from the 18 if I need it. The post about using the 40 rods got me to thinking. Thanks for the info. ;)

Offline dyoung14

  • Newbie
  • *
  • Posts: 23
  • Karma: 0
    • View Profile
Re: another rod question
« Reply #5 on: July 02, 2009, 05:52:40 pm »
That's all fine and dandy but it probably actually decreases overall power unless you mill the pistons down. On a flathead I generally try to keep the piston in the bore atleast 0.005". To do that you would have to mill off 0.055" which is still safe.  I'm not sure where the failure point is, but if you mill .070" off you might make 2 races before the top caves in.  Just a little food for thought.

how is it going to kill my power? it seems to me that it has increased my power greatly

Offline dropzone

  • Newbie
  • *
  • Posts: 18
  • Karma: 0
    • View Profile
Re: another rod question
« Reply #6 on: July 02, 2009, 08:24:06 pm »
 I think mmsports is thinking about the piston interfearing with the flow in the chamber but .050 is not alot to come out of the block. I can see where it would make more power because of the compression. Might want to watch for detonation due to the rise in the compression. I dont know though may not be enough to matter.

Offline dyoung14

  • Newbie
  • *
  • Posts: 23
  • Karma: 0
    • View Profile
Re: another rod question
« Reply #7 on: July 03, 2009, 10:40:30 am »
like i have said before mine is running perfect since i built it havent had any problems

mmsports

  • Guest
Re: another rod question
« Reply #8 on: July 03, 2009, 10:05:14 pm »
how is it going to kill my power? it seems to me that it has increased my power greatly

Sure you added more compression, but it's a flathead you can actually get more power with a lower ratio than with a higher one.
Flatheads do not have a real good flow velocity any way, and when you start popping pistons out of the deck, you decrease that flow. Remember the valves are beside the piston not over top of it, and the air/fuel mixture has to travel sideways to the piston, instead of being dumped straight down on top of it.

2 years ago we took a 40 ci engine and just a couple hundred dollars, and smoked guys running 42's and 46's that was popping the pistons out of the deck. We had the same cams and carbs, and they all swore up and down that it had to be over 50 ci.    On a flatty I like big chamber heads, and I generally like to keep the piston down in the bore about .010. We might not be the champs but the 40 ci engine was a top 5 out of more than 50.

Offline dyoung14

  • Newbie
  • *
  • Posts: 23
  • Karma: 0
    • View Profile
Re: another rod question
« Reply #9 on: July 04, 2009, 01:39:37 am »
well i raced again tonight and something bad happened :( no the engine didnt blow is still running like a top, i blew the tranny tonight  :doh: to much power :D anywho i took off really hard from the starting line dumped the clutch at about 3000 rpm and then nailed it and herd a funny sound but i just held in to it came out of first corner and brought it up to about 5400 rpm and i herd lots of grinding out of transmission and was slowing down so i limped off the track and got stoped, so now i got to put my spare in there i may or may not have it back together before next weekend, but i do have a sweet running opposed twin with both pistons commin out of the deck :D everyone has opinions on how the want to build there engine and this is mine yall might not beilieve in it but i do

Offline dropzone

  • Newbie
  • *
  • Posts: 18
  • Karma: 0
    • View Profile
Re: another rod question
« Reply #10 on: July 05, 2009, 11:35:37 pm »
dyoung thats all that matters. If it works dont change it. thanks for the info

Offline dyoung14

  • Newbie
  • *
  • Posts: 23
  • Karma: 0
    • View Profile
Re: another rod question
« Reply #11 on: July 06, 2009, 12:34:12 am »
i dont plan on changing my engine setup it runs to good :D >:D