Checking valve clearances in the cold - Snowblower Forum : Snow Blower Forums
Reply
 
LinkBack Thread Tools
post #1 of 12 Old 12-08-2018, 09:13 PM Thread Starter
Senior Member
 
Join Date: Dec 2013
Location: Massachusetts
Posts: 751
Post Thanks / Like
Thanks (Given): 61
Thanks (Received): 58
Likes (Given): 112
Likes (Received): 76
Checking valve clearances in the cold

I noticed my exhaust was turning a bit red while running at night. I checked the exhaust valve clearance on a Tecumseh HMSK90. It has been cold out, like in the 20's. The spec is .004 to .008. I measured .003 today. What adjustments should I consider for the cold temps. I am thinking I will lap it for a few minutes and measure it again.....should I am for the high end of the clearance when I go to grind the end of the valve?


This is a fixed jet carb so I can not make the mixture a bit richer. Just in case you were thinking that.

Current machines
Ariens 926LE

Yard Machine 22" upgraded with 6.5 HP Predator
Toro-8-2-4 is offline  
Sponsored Links
Advertisement
 
post #2 of 12 Old 12-08-2018, 09:41 PM
Senior Member
 
Join Date: Mar 2014
Location: Lowell area, MA
Posts: 3,252
Post Thanks / Like
Thanks (Given): 118
Thanks (Received): 277
Likes (Given): 358
Likes (Received): 634
I wouldn't worry about trying to account for cold temperatures, when measuring.

The clearance seems to gradually increase with these, over time. So aiming towards the larger side of the spec is probably not a bad idea. Too-large clearance will make the compression release less effective, so harder to pull. Too-small clearance will make the valve stay open when hot, which is bad, as you've seen.

Just don't take too much off the valve stem! It's a lot harder to put the metal back on
Edit: Just checked here:

https://www.engineeringtoolbox.com/l...on-d_1379.html
If the valve was 4" long, it would be 0.0024" shorter at 20F, vs 70F. So depending on the valve's actual length, maybe it is worth factoring in something for temperature. But as your symptoms do sound consistent with the valve staying open a little, I wouldn't consider your 0.003" clearance to "really" be a 0.005" clearance, for instance.

Ariens 1024 Pro
Toro Power Clear 221QR
Toro Power Curve 1800

Last edited by RedOctobyr; 12-08-2018 at 09:52 PM.
RedOctobyr is offline  
post #3 of 12 Old 12-09-2018, 10:01 AM Thread Starter
Senior Member
 
Join Date: Dec 2013
Location: Massachusetts
Posts: 751
Post Thanks / Like
Thanks (Given): 61
Thanks (Received): 58
Likes (Given): 112
Likes (Received): 76
Interesting. There is more to it than just the expansion and contraction of the valve. There is a whole stack up of components that determine the valve lash. Some are aluminum and some are steel. But to think practically, it can't be that much. I am going to aim at removing about .003 and go from there.


I had one person tell me some glowing mufflers are normal. Never heard of that on a newer engine. Maybe in a 1970's or older design.

Current machines
Ariens 926LE

Yard Machine 22" upgraded with 6.5 HP Predator
Toro-8-2-4 is offline  
post #4 of 12 Old 12-09-2018, 10:11 AM
Senior Member
 
Jackmels's Avatar
 
Join Date: Feb 2013
Location: Ma.
Posts: 2,101
Post Thanks / Like
Thanks (Given): 111
Thanks (Received): 168
Likes (Given): 373
Likes (Received): 705
You Can Increase the Valve Clearance without Tearing everything apart. Remove the carb, and the valve cover. Then get a file between the valve stem and lifter, (The spring will keep tension on both surfaces) and file away. Or, You can Tear it apart. (Stick a magnet in when you are done to secure filings.)
Jackmels is online now  
post #5 of 12 Old 12-09-2018, 11:05 AM
Senior Member
 
Join Date: May 2015
Location: NE Illinois
Posts: 650
Post Thanks / Like
Thanks (Given): 45
Thanks (Received): 62
Likes (Given): 185
Likes (Received): 126
Agreed that the other components will expand and contract with temperature changes, so the net effect of temperature change when setting the lash will probably be less. I wouldn't even want to start to do that complete calculation. I grind to the center of the spec, and focus on getting a clean, square grind on the valve end.

Note that the Tecumseh technician manual says "Valve clearance (between the valve stem and valve lifter) should be set or checked when the engine is cold."

Paul
----------------------------------------------------------------
1995 Toro 724, 1988 Toro 521
1980 Toro 421, 1995 Craftsman 524
1997 Toro CCR 2500 & 1994 Toro CCR Powerlite
paulm12 is online now  
post #6 of 12 Old 12-09-2018, 08:17 PM Thread Starter
Senior Member
 
Join Date: Dec 2013
Location: Massachusetts
Posts: 751
Post Thanks / Like
Thanks (Given): 61
Thanks (Received): 58
Likes (Given): 112
Likes (Received): 76
Quote:
Originally Posted by paulm12 View Post
Agreed that the other components will expand and contract with temperature changes, so the net effect of temperature change when setting the lash will probably be less. I wouldn't even want to start to do that complete calculation. I grind to the center of the spec, and focus on getting a clean, square grind on the valve end.
Note that the Tecumseh technician manual says "Valve clearance (between the valve stem and valve lifter) should be set or checked when the engine is cold."
Jack, Funny you made this suggestion. As I was taking it apart I had that exact thought for a few seconds. I was wondering how hard the valve end may be and would my file be able to cut it? I ended up taking it out

and doing it on my bench grinder. Maybe next time.

Paulm,

Right, but how cold? Inspection rooms are suppose to be at 68 deg. F. as it can matter.

Ideally if you could chuck it up in a lathe and take a nice smooth and square cut you could be done fast and you have good control and surface finish.

Current machines
Ariens 926LE

Yard Machine 22" upgraded with 6.5 HP Predator

Last edited by Toro-8-2-4; 12-09-2018 at 08:22 PM.
Toro-8-2-4 is offline  
post #7 of 12 Old 12-10-2018, 07:49 PM
Member
 
Join Date: Jan 2018
Location: New England
Posts: 55
Post Thanks / Like
Thanks (Given): 0
Thanks (Received): 6
Likes (Given): 0
Likes (Received): 15
Good post. Just to expand on this a little bit (no pun intended), there are two basic problems that cause valve lash (clearance) to change: 1) the valve is steel while the engine body is aluminum, and they expand at different rates and 2) the valves will get far, far hotter than the overall engine temps.

For those curios, steel expands at the rate of ~ 6.5 millionths of an inch, per inch of length, per degree F of temp. change. For example, a 3" long valve, running at 900F and starting at 70F will have a temp. change of 830 degrees F. So 0.0000065 inches times 3 inches times 830 is ~ 0.016" or sixteen thousandths of an inch. There goes all the clearance and then some. But Aluminum expands at twice that rate so while the aluminum engine will not get nearly that hot, it will expand at twice the rate, and there is a lot more engine length than there is valve length. So the idea is to get as close to zero lash as possible without the possibility of actually getting to zero under the worst operating conditions of the engine. As was already mentioned by the quote below, the amount of lash is not important, what is important is that there is some lash.

Brian

Quote:
Originally Posted by RedOctobyr View Post
I wouldn't worry about trying to account for cold temperatures, when measuring.

The clearance seems to gradually increase with these, over time. So aiming towards the larger side of the spec is probably not a bad idea. Too-large clearance will make the compression release less effective, so harder to pull. Too-small clearance will make the valve stay open when hot, which is bad, as you've seen.

Just don't take too much off the valve stem! It's a lot harder to put the metal back on
Edit: Just checked here:

https://www.engineeringtoolbox.com/l...on-d_1379.html
If the valve was 4" long, it would be 0.0024" shorter at 20F, vs 70F. So depending on the valve's actual length, maybe it is worth factoring in something for temperature. But as your symptoms do sound consistent with the valve staying open a little, I wouldn't consider your 0.003" clearance to "really" be a 0.005" clearance, for instance.
LDRider is offline  
post #8 of 12 Old 12-10-2018, 08:32 PM
Senior Member
 
Join Date: Mar 2014
Location: Lowell area, MA
Posts: 3,252
Post Thanks / Like
Thanks (Given): 118
Thanks (Received): 277
Likes (Given): 358
Likes (Received): 634
Quote:
Originally Posted by Toro-8-2-4 View Post
Ideally if you could chuck it up in a lathe and take a nice smooth and square cut you could be done fast and you have good control and surface finish.
I was fortunate enough that a friend at work set my valve up on a surface grinder, and took off the required amount that way. Probably even a better result than in a lathe.

I don't remember if the end of the valve seemed hardened, unfortunately.

I guess I'd be nervous about filing it with the valve still installed, I'd be concerned about filings getting into areas that they shouldn't.

I struggled to remove my valve, and to re-install it, but I didn't have a proper spring compressor. So it was a very jury-rigged deal, with a C-clamp, and some big flathead screwdrivers, as I recall. No picnic If you have access to a spring compressor, that would be a lot easier.

Ariens 1024 Pro
Toro Power Clear 221QR
Toro Power Curve 1800
RedOctobyr is offline  
post #9 of 12 Old 12-11-2018, 01:01 AM
Senior Member
 
drmerdp's Avatar
 
Join Date: Feb 2014
Location: Northern NJ
Posts: 1,288
Post Thanks / Like
Thanks (Given): 6
Thanks (Received): 144
Likes (Given): 24
Likes (Received): 294
Quote:
Originally Posted by Jackmels View Post
You Can Increase the Valve Clearance without Tearing everything apart. Remove the carb, and the valve cover. Then get a file between the valve stem and lifter, (The spring will keep tension on both surfaces) and file away. Or, You can Tear it apart. (Stick a magnet in when you are done to secure filings.)
I’ve done this many times.

If the valve is only out of spec and not zero lash throwing flames I wouldn’t bother tearing down and lapping.

Honda HSS1328AATD | Honda HS720 | Toro Powerlite | Simplicity 860se


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
drmerdp is offline  
Post Thanks / Like - 1 Thanks, 1 Likes, 0 Dislikes
Thanks Jackmels thanked for this post
Likes Jackmels liked this post
post #10 of 12 Old 12-11-2018, 07:55 PM
Senior Member
 
Join Date: Nov 2016
Posts: 116
Post Thanks / Like
Thanks (Given): 1
Thanks (Received): 7
Likes (Given): 1
Likes (Received): 19
Wow although it can be done that way It certainly isnít the easy way out. Especially with someone who really donít feel they can manage taking the engine apart and doing the top end of the motor.

New Jersey, Toro 8/24, Ariens 5/22, small engine repairs
Bluejoe is offline  
Sponsored Links
Advertisement
 
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Snowblower Forum : Snow Blower Forums 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










Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page



Posting Rules  
You may post new threads
You may 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