Home
Don't have an account? Create one now! It's always free!


Forgot Password
Ed's Auto Parts - Mention MOTORGEN for a Discount!
Motorgen Sponsor: McLeod Racing
Motorgen Sponsor: American Muscle - Add style and performance to your Stang
Motorgen Sponsor: Hall Fabrication & Racing
Motorgen Sponsor: Injectors Plus - Performance Fuel Delivery Systems
Reply
 
Thread Tools
Old 06-08-2008, 02:18 AM   #1
enkeivetteenkeivette is offline
Super Moderator
 
enkeivette's Avatar
 
Join Date: Dec 2007
Posts: 6,850
Default Piston rock.
So I'm measuring my piston to deck height today so I can figure out exactly what my static CR is. I hold the straight edge over the center of the piston, and I can barely fit a 25/1000 feeler guage in there, move the straight edge to the top of the piston, and the feeler guages doesn't fit!

So I look closely and I notice that the piston is actually tilting forward! Come to find out that this is actually normal. Pistons (especially forged pistons) have enough clearance to pivot off the rod and rock back and forth in the bore. So I push on the top of the piston, and it tlits back!

Sorry, I just found that really surprising.
  Reply With Quote
Old 06-08-2008, 11:29 AM   #2
VettezukiVettezuki is offline
I, Vettezuki
 
Vettezuki's Avatar
 
Join Date: Feb 2006
Posts: 14,754
Default
Quote:
Originally Posted by enkeivette View Post
So I'm measuring my piston to deck height today so I can figure out exactly what my static CR is. I hold the straight edge over the center of the piston, and I can barely fit a 25/1000 feeler guage in there, move the straight edge to the top of the piston, and the feeler guages doesn't fit!

So I look closely and I notice that the piston is actually tilting forward! Come to find out that this is actually normal. Pistons (especially forged pistons) have enough clearance to pivot off the rod and rock back and forth in the bore. So I push on the top of the piston, and it tlits back!

Sorry, I just found that really surprising.
This is only when it's cold. Forged pistons expand much more than cast under heat, that's why that "cold" tolerance is built into them. It's also why when putting forged pistons into a motor with knock sensors tuned for cast (like a stock LS1), you have to change their knock sensitivity or some such thing or the computer will unnecessarily pull timing and dump full. It's also why you don't want to jump all over a forged motor until it is thoroughly warmed up.
__________________
Motorgen on
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

Motorgen on
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

Motorgen Project Car
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
(active)
Motorgen Project Car
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
(back burner)
  Reply With Quote
Old 06-08-2008, 12:48 PM   #3
enkeivetteenkeivette is offline
Super Moderator
 
enkeivette's Avatar
 
Join Date: Dec 2007
Posts: 6,850
Default
Very true, but still I had no idea there was that kind of tolerance.
  Reply With Quote
Old 06-09-2008, 11:25 AM   #4
BRUTAL64BRUTAL64 is offline
Neanderthal
 
BRUTAL64's Avatar
 
Join Date: Mar 2008
Posts: 5,320
Default
Quote:
Originally Posted by enkeivette View Post
Very true, but still I had no idea there was that kind of tolerance.
Clearence is .004 to .0065. Yes, the piston does rock.
__________________
64 Vette Roadster 400 ci
1990 F150 351 ci SuperCharged
48 Harley Pan Head 76 ci
2016 Nissan Altma
  Reply With Quote
Old 06-09-2008, 12:40 PM   #5
VettezukiVettezuki is offline
I, Vettezuki
 
Vettezuki's Avatar
 
Join Date: Feb 2006
Posts: 14,754
Default
Quote:
Originally Posted by glenn64vette View Post
Clearence is .004 to .0065. Yes, the piston does rock.
What he describes "sounds" like a lot more. Wonder if he's got issues. Well, I know he's got issues but you know what I mean.
__________________
Motorgen on
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

Motorgen on
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

Motorgen Project Car
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
(active)
Motorgen Project Car
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
(back burner)
  Reply With Quote
Old 06-10-2008, 09:03 AM   #6
BRUTAL64BRUTAL64 is offline
Neanderthal
 
BRUTAL64's Avatar
 
Join Date: Mar 2008
Posts: 5,320
Default
Quote:
Originally Posted by Vettezuki View Post
What he describes "sounds" like a lot more. Wonder if he's got issues. Well, I know he's got issues but you know what I mean.
The .004 to .0065 is at 90* of wrist pin. The rocking of the piston is normal. Weird, but normal.

Weird is relative to what is normal.
__________________
64 Vette Roadster 400 ci
1990 F150 351 ci SuperCharged
48 Harley Pan Head 76 ci
2016 Nissan Altma
  Reply With Quote
Reply

« Previous Thread | Next Thread »


Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts
vB code is On
Smilies are On
[IMG] code is On
HTML code is Off


All times are GMT -7. The time now is 01:55 AM.

Contact Us - Home - Archive - Top