What causes the OHV's to go out of gap ? - MyTractorForum.com - The Friendliest Tractor Forum and Best Place for Tractor Information
Backyard Round Table - L & G Tractor Related Topics Lawn and Garden Tractor Related Topics General Discussion Board

Reply
 
LinkBack Thread Tools Display Modes
post #1 of 18 Old 06-17-2019, 10:32 AM Thread Starter
Jerk of all trades
 
smcgill's Avatar
 
Join Date: Apr 2012
Location: Easton Mass.
Posts: 43
Question What causes the OHV's to go out of gap ?

I think I worded it ok.
What causes the valves go out of gap .. I seam to have to fix this problem a lot..
How do you stop it from doing so often ?
This is on my Craftsman Lawn tractor.

Chrasftman 18.5 , 42"deck..Husky YTH1848XP tractor , 142,350 saws
Easy when you have Husky saws and tractors!
smcgill is offline  
Sponsored Links
Advertisement
 
post #2 of 18 Old 06-17-2019, 10:43 AM
Senior MTF Member
 
Join Date: Jun 2012
Location: Florida
Posts: 252
Re: What causes the OHV's to go out of gap ?

Loose keepers?
ChuckT is offline  
post #3 of 18 Old 06-17-2019, 10:46 AM
15,000 +posts!
 
Tractor-Holic's Avatar
 
Join Date: Jan 2008
Location: MA
Posts: 19,130
Re: What causes the OHV's to go out of gap ?

Lots of things can cause the valve lash to change..

Rocker arm studs pulling out of the cylinder head.

Rocker arm adjusting screws wearing down where they touch the valve stem or where the push rod seats..or the adjustment screw doesn't hold its setting.

Cam lobes wearing down.

Push rods bent.

Valve lifter or follower worn down.

Excessive valve guide clearance..


Tractor-Holic is online now  
Sponsored Links
Advertisement
 
post #4 of 18 Old 06-17-2019, 10:54 AM
Senior MTF Member
 
Join Date: Mar 2016
Location: Michigan
Posts: 466
Re: What causes the OHV's to go out of gap ?

Couple of random thoughts here.

Assume this is an OHV engine and requires adjustment much more frequently than the manual recommendations, poor fitting adjusting nuts or jam nuts or the studs might be working loose. Depending on engine, studs may be pressed in or threaded.

You might try putting a mark on the nut/stud after the next time you adjust. After a time, if the valves go out of adjustment again, check to see if the marks are misaligned, indicating the adjusting nut is loosing grip and allowing it to back off. At the base of the stud where it enters the head casting, you might try the same thing. Mark it with a scratched line. A pressed in stud will be harder to detect, and may require a depth gauge to compare before and after stud to casting height. A screwed in stud will show the misaligned marks if it is working loose from the head casting.

Check all contact surfaces too. Improperly heat treated valve tips or other contact points can wear.

Not sure if overheating can impact valve adjustment, maybe someone with more experience with overheating can comment.

X 500 48" Deck 48" blade
Cyclone Rake
Stihl BR 600
Sears Suburban Super 12 1968
Craftsman 1990 something LG Tractor 46" deck
Original Kohler 8hp Giant Vac early 1960s
Alien5044 is offline  
post #5 of 18 Old 06-17-2019, 10:07 PM
MTF Member
 
Join Date: May 2012
Location: Nova Scotia
Posts: 56
Re: What causes the OHV's to go out of gap ?

On my old tractor with a 17 hp Briggs I used to have to set the valves once a year otherwise it would build compression and not even turn over. Their tricky devils to set valve lash on.

I ended up setting it on the loose side and itís been good for a year and a half so far.
Damion1krr is online now  
post #6 of 18 Old 06-20-2019, 12:59 AM
3K Poster!!!!
 
Join Date: Jun 2013
Location: Ohio
Posts: 3,145
Re: What causes the OHV's to go out of gap ?

They should not need frequent adjustment. Most of the wear occurs in the first couple of years and then everything is polished up nicely and little wear occurs for many years.

Most valves wear in the valve sealing area margin and all that stuff. They sink further into the head as they wear and make clearance smaller.
The OHV briggs don't do that enough to make up for the metal wear off of the rocker arm and push rod and rocker arm and valve stem cap mainly and I assume the push rod and lifter too. It wears so much that the gaps always get larger NOT smaller.
That is why they are hard to start when out of adj. The gap is too much for the ACR to move the valve open enough.

EVERY time I am in briggs valve cover I remove rocker arm so I can check stud for tightness. Epidemic of the (esp exhaust) loosening up.
Tighten well or take out clean and loctite then tighten.

Now assuming you have the hardened valve stem cap on each valve stem and the oil is not nasty black and gritty, they should stay in adjustment for years.
TobyU is offline  
post #7 of 18 Old 06-20-2019, 01:03 AM
3K Poster!!!!
 
Join Date: Jun 2013
Location: Ohio
Posts: 3,145
Re: What causes the OHV's to go out of gap ?

Quote:
Originally Posted by Damion1krr View Post
On my old tractor with a 17 hp Briggs I used to have to set the valves once a year otherwise it would build compression and not even turn over. Their tricky devils to set valve lash on.

I ended up setting it on the loose side and itís been good for a year and a half so far.
If it's an ohv 31xxxxor 33xxxx that is opposite of how it is supposed to work.
Loose valves MAKE it hard to start. Well loose intake actually.
I like exhaust valve to be on the loose side as they cool when they are closed..or so the story goes. I don't have a way to test that rule of thumb.
It ACR pushes up a little bitty bit on the intake lifter and if the clearance is too great is just takes up the gap and doesn't even move the rocker arm enough to open valve.
TobyU is offline  
post #8 of 18 Old 06-20-2019, 05:52 PM
MTF Member
 
Join Date: May 2012
Location: Nova Scotia
Posts: 56
Re: What causes the OHV's to go out of gap ?

I adjusted them on the looser side of the specs. If the called for say 3-7 thousandth I went on the 7 side.
Damion1krr is online now  
post #9 of 18 Old 06-20-2019, 05:58 PM
MTF Member
 
Join Date: Sep 2018
Posts: 72
Re: What causes the OHV's to go out of gap ?

7 will work, but tighter will keep it in adjustment longer
Cranman is offline  
post #10 of 18 Old 06-20-2019, 06:26 PM
Senior MTF Poster
 
Join Date: Jan 2006
Location: IL
Posts: 12,736
Re: What causes the OHV's to go out of gap ?

Quote:
Originally Posted by Damion1krr View Post
I adjusted them on the looser side of the specs. If the called for say 3-7 thousandth I went on the 7 side.
Bad idea.

Walt Conner
Walt 2002 is online now  
post #11 of 18 Old 06-20-2019, 09:23 PM
3K Poster!!!!
 
Join Date: Jun 2013
Location: Ohio
Posts: 3,145
The intake and the exhaust do not both set at the same spec on a single. I think we were talking about a single. Or at least over head valves in general and singles definitely do not set to the same spec intake and exhaust.
Most are intake .003-.005, exhaust .005-.007
You should keep the intake at least a tight .005 so you can compression release will work longer.
TobyU is offline  
post #12 of 18 Old 06-21-2019, 07:15 PM
MTF Member
 
Join Date: May 2012
Location: Nova Scotia
Posts: 56
Re: What causes the OHV's to go out of gap ?

I was just using the one measurement as an example. I set both valves different but more on the looser side of the specs
Damion1krr is online now  
post #13 of 18 Old 06-22-2019, 08:29 AM
ex spelling bee champ
 
Ingersoll444's Avatar
 
Join Date: Mar 2005
Location: NY
Posts: 31,100
Send a message via AIM to Ingersoll444 Send a message via MSN to Ingersoll444
Re: What causes the OHV's to go out of gap ?

As was said... Normally they stabilize after the first few adjusting till the engine gets to the point that wear takes over. Im guessing they are getting looser? Really unless there is unknown background on the engine, or you are using it in a different environment then expected, you can really set the specs on the tighter end of the range and be fine. Also checking clearances can be a little bit of a art form. Are you sure your not going to loose to start? the gauge should barely go in.. I normally check with the go/no go system... Ill take a gauge that's the tight end, and one at the loose end.. set it so the tight just slips in, and the bigger one will not... that will get you smack on in the center of the range.

Paul



Visit The Case Ingersoll Colt Forum.

SUPER Of The Month 10/2011
Ingersoll444 is offline  
post #14 of 18 Old 06-22-2019, 08:43 AM
Senior MTF Poster
 
Join Date: Jan 2006
Location: IL
Posts: 12,736
Re: What causes the OHV's to go out of gap ?

" Also checking clearances can be a little bit of a art form. Are you sure your not going to loose to start? the gauge should barely go in.. I normally check with the go/no go system... Ill take a gauge that's the tight end, and one at the loose end.. set it so the tight just slips in, and the bigger one will not... that will get you smack on in the center of the range."

I agree, I set the Intake close to the minimum.

Walt Conner
Walt 2002 is online now  
post #15 of 18 Old 06-22-2019, 10:01 AM
MTF Junior Poster
 
Join Date: Jul 2017
Location: Missouri
Posts: 7
Re: What causes the OHV's to go out of gap ?

weak valve springs are a possibility as well
BuzzGold is offline  
Sponsored Links
Advertisement
 
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the MyTractorForum.com - The Friendliest Tractor Forum and Best Place for Tractor Information forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in











Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode



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 On

 
For the best viewing experience please update your browser to Google Chrome