R/C Tech Forums

Go Back   R/C Tech Forums > General Forums > Nitro Off-Road

Reply
 
Thread Tools Search this Thread
Old 04-03-2009, 05:48 PM   #1
Tech Adept
 
junier00's Avatar
 
Join Date: Mar 2009
Posts: 197
Trader Rating: 20 (100%+)
Default Needs help checking rod/crank.

Hey guys, I'm rebuilding an engine and need to know to to check that the crank and the rod are still in good condition.

How do I judge this? How much play should the rod have where it mounts to the crank?

Thanks for the help.

JR.
junier00 is offline   Reply With Quote
Old 04-03-2009, 06:47 PM   #2
Tech Adept
 
chunk t's Avatar
 
Join Date: Nov 2008
Location: Elgin, IL
Posts: 225
Default

Expect a few different answers.

-Some of us will measure the .000" of wear delta from original.
-Some of us measure concentrisity (roundness) of the crank pin
-Some of us will simply say "it feels too loose."

I like to measure concentrisity of the pin. Once you reach a differance of about 5% I consider the pin ready for replacement. Any greater than 5% and you risk pin failure.

What to look for... 1) scaring on the pins. a good pin will have a nice burnished finish. 2) gaulling of the rod bearing surface 3) cracks & or voids (missing pieces) of rod bearing surface. 4) segment of rod bushing completely worn away. **some rods do not have inset bushings, but inspection remains the same**

caviots- 1) you need a min of .0015"-.002" play between the pin & rod bushing so proper lubrication can occure. 2) the crank pins are ALWAYS under load 360-degrees of crank rotation. Trust me... you won't eat a pistion because of a loose fit. 3) as the rod and pins wear the port timings slightly change and CR gradually falls (5%-10%). So don't be surprised if you need to change nitro %, plug temp & pipe as the gallons flow through the engine.

Just because a rod and pin are loose, it does not mean they are ready for a change. This just means they are good and borken-in. The rods and pins wear together as a set, the moment you replace the crank or rod, they have to wear (cut) new bearing surfaces. This mis-match of new and old will cause the two parts to wear excessively fast until the bearing surfaces match; by this point the wear will probably be great enough the "good old part" is now a "bad old part", out of tolerance and in need of replacing.

I guess my short answer is don't replace unless you have good reason. and when you do replace... replace everything; the rod, crank and wrist pin.
__________________
chuck "chunk" thomas
.......
1:10, 2-wd Stadium Trucks
B-Mod Tunnels
.......
If ignorance is bliss... I must be in heaven!
chunk t is offline   Reply With Quote
Reply

Similar Threads
Thread Thread Starter Forum Replies Last Post
"the tuning bible" houston Onroad Nitro Engine Zone 311 04-24-2017 11:18 PM
Yay Dvx400Rider Nitro Off-Road 7 02-27-2009 08:25 PM
Please Help Muah! Speedjunkyz Nitro On-Road 36 09-05-2008 07:13 AM



Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are Off



All times are GMT -7. It is currently 08:53 AM.


Powered By: vBulletin v3.9.2.1
Privacy Policy | Terms of Use | Advertise Content © 2001-2011 RCTech.net