VansAirForceForums  
Home > VansAirForceForums

- POSTING RULES
- Donate yearly (please).
- Advertise in here!

- Today's Posts | Insert Pics

  #1  
Old 03-02-2017, 07:01 AM
acam37's Avatar
acam37 acam37 is offline
 
Join Date: Aug 2012
Location: Lufkin Tx
Posts: 689
Default Cable or tach?

I have an issue with my mechanical tachometer. At full power (constant speed) it will only spool up to 2400, then after about a minute the needle will jump to 2600rpm with no noticeable pitch change from the prop. We verified the prop is turning 2670rpm static with a hand held rpm meter. So my question is, can the cable be the culprit or is the tachometer going bad?
__________________
Arlie Conner (A&P)
RV-4 (N124TT) Sold
RV-8 (N269CP) Sold
RV-4 (N684ML) completed 3-17-19
KOCH Nacogdoches
Reply With Quote
  #2  
Old 03-02-2017, 07:17 AM
SuperDave SuperDave is offline
 
Join Date: Feb 2011
Location: Brandon, FL
Posts: 68
Default Tach

Recently had a similar problem. I'm 99% sure it's the tach.
Reply With Quote
  #3  
Old 03-02-2017, 07:47 AM
Kyle Boatright Kyle Boatright is offline
 
Join Date: Aug 2005
Location: Atlanta, GA
Posts: 4,219
Default

Quote:
Originally Posted by SuperDave View Post
Recently had a similar problem. I'm 99% sure it's the tach.
I had the same issue back in the day. Tach problem in my case.
__________________
Kyle Boatright
Marietta, GA
2001 RV-6 N46KB
2019(?) RV-10
Reply With Quote
  #4  
Old 03-02-2017, 08:15 AM
Vlad's Avatar
Vlad Vlad is offline
 
Join Date: Oct 2008
Location: Utah
Posts: 8,151
Default

Could be a cable problem as well. I replaced and repositioned my tach couple years ago which required a different cable length. I ordered a custom made cable and it was a bit longer. I routed it with a steeper bend. It caused the cable to disingage and slip. Problem was solved with correct length.
__________________
Where is N666BK?

Не имей сто рублей, а имей сто друзей.
Reply With Quote
  #5  
Old 03-02-2017, 08:44 AM
acam37's Avatar
acam37 acam37 is offline
 
Join Date: Aug 2012
Location: Lufkin Tx
Posts: 689
Default

I am pretty sure it's the tach and not a cable but wanted to get a second opinion and see if anyone else had this problem and wound up being a cable. I've got a WTB in the classifieds but if no response in the next few days I will go ahead and buy one. At first I thought we had a more serious problem but after re-adjusting the fine pitch stops on the prop, nothing changed on the tach so we put it back where it was. There is a 200rpm drop across the board compared to the rpm meter.
__________________
Arlie Conner (A&P)
RV-4 (N124TT) Sold
RV-8 (N269CP) Sold
RV-4 (N684ML) completed 3-17-19
KOCH Nacogdoches
Reply With Quote
  #6  
Old 03-02-2017, 08:55 AM
jswartz jswartz is offline
 
Join Date: Aug 2011
Location: San Diego, CA
Posts: 11
Default

I had a similar situation in the tach of my Cessna 120. It would jump up and then back to the actual reading. Gradually the jumps became more significant. It turned out there is an oil seal, I think on the engine side of the cable, that permitted oil to enter the cable and into the tach itself. He replaced the seal, cleaned the oil out of the "broken" tach, and it has been perfect since. So in my case, we did not end up replacing the tach, we replaced the oil seal and cleaned the tach.

Jerry
Reply With Quote
  #7  
Old 03-02-2017, 09:37 AM
Far North Texan Far North Texan is offline
 
Join Date: Jun 2015
Location: Alberta
Posts: 84
Default

Ditto on oil possibly going into the cable. Had the exact same thing happen. Check that, its easy.
__________________
RV-6A slow build,
serial # 21681. First flight March 1993
Dec 2019 donation paid
Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

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
Forum Jump


All times are GMT -6. The time now is 06:31 AM.


The VAFForums come to you courtesy Delta Romeo, LLC. By viewing and participating in them you agree to build your plane using standardized methods and practices and to fly it safely and in accordance with the laws governing the country you are located in.