Antique Engines and Old Iron
[Home] - [HELP] - [Forums] - [Groups] - [Classified Ads] - [Subscribe] - [Books] - [Sponsors] -

Go Back   SmokStak > SmokStak® Antique Engine Community > Small Air Cooled Gasoline Engines > Garden Tractors and Mowers
Forgot Password? Join Us!

Notices

Garden Tractors and Mowers Vintage lawn and garden tractors, mowers, snow blowers, snowmobiles and other old machinery that is driven by small air cooled engines.

Garden Tractors and Mowers

Sears ST12 Tecumseh Starter Difficulty Mystery and Carburetor Blow Back


this thread has 61 replies and has been viewed 2502 times

Reply
 
Thread Tools Display Modes
  #41  
Old 06-20-2019, 05:08:03 PM
Markoh Markoh is offline
Registered
 
Join Date: May 2019
Location: Lexington, South Carolina
Posts: 24
Thanks: 35
Thanked 3 Times in 3 Posts
Default Re: Sears ST12 Tecumseh Starter Difficulty Mystery and Carburetor Blow Back

[QUOTE=Georgia SS;1582742]Hey Guys
fill the gap between the valve stem and lifter on both valves to 0 clearance to check if the comp. release is worn down, don't put cover back on, the motor will run fine without a cover, may leak a bit of oil, sure is a lot of clearance on both valves, i only run about 5 and 10, works for me, too small gage battery cables will also make problems.[Quote]
Thank you for your input. Would not have thought of that.

I assure you I be tired of beating this one too. I was desperate enough to contact a guy who had one for sale north of me to make sure the engine was not turning backwards. Why do I persist? I suppose it's in the blood. Maybe that's why they call it being a "gear head".

0 clearance it will be. If that works I will set them to 5 and 10.

The battery cables better not be a problem. They are the best Sears Craftsman made from back when Sears Craftsman was pretty darn good. However, I will check their resistance just in case.
Reply With Quote
Sponsored Links
  #42  
Old 06-20-2019, 10:40:29 PM
FWurth's Avatar
FWurth FWurth is offline
One Millionth Post
 
Join Date: Feb 2007
Location: Freeburg, Illinois, USA
Posts: 6,531
Thanks: 7,568
Thanked 6,044 Times in 3,101 Posts
Default Re: Sears ST12 Tecumseh Starter Difficulty Mystery and Carburetor Blow Back

We have an old yard man with an electric start Briggs . ran like new for years but the battery failed often, used a motor cycle battery, very pricey. Always had starter issues, so I installed a regular lawn type battery. Still issues so I replaced all cables with much heavier gauge4 ones and cured it for years. Recently it wouldn't crank after sitting a few days. Found out the carb. would leak down into the engine and it would hydro lock till it puked out the excess. Finally found it after it destroyed 2 starters. Never over look the simple stuff.
Reply With Quote
The Following User Says Thank You to FWurth For This Post:
  #43  
Old 06-22-2019, 04:56:07 PM
CharlieB CharlieB is offline
Registered
 
Join Date: Dec 2014
Location: Severn, Maryland, USA
Posts: 374
Thanks: 34
Thanked 185 Times in 140 Posts
Default Re: Sears ST12 Tecumseh Starter Difficulty Mystery and Carburetor Blow Back

Starter/compression release issue should not prevent engine from firing as long as rotation past full compression stroke occurs.
The ingredients for combustion are air, fuel, compression, spark and timing. So far, all have been verified to be present except correct timing.

Unlike car engines, there is no timing mark on the flywheel, so the head needs to come off for the the spark timing to be checked/set. If you don't have the repair manual showing how to set the timing on a Tecumseh, YouTube has videos showing how it's done. No timing light involved.

If you find that the plug is firing too far before TDC, (i.e. before the compression stroke is complete), that could also explain the starter problem.
Reply With Quote
The Following User Says Thank You to CharlieB For This Post:
  #44  
Old 06-22-2019, 05:25:40 PM
Elevated Elevated is offline
Registered
 
Join Date: Jun 2019
Location: Bloomington, Indiana
Posts: 104
Thanks: 40
Thanked 73 Times in 45 Posts
Default Re: Sears ST12 Tecumseh Starter Difficulty Mystery and Carburetor Blow Back

I think the op claimed early on in this thread, that the engine would not turn a complete revolution, unless the plug was removed or he held his hand against the carb and prevented any air intake. Otherwise it would roll up against compression and stop.
Reply With Quote
The Following User Says Thank You to Elevated For This Post:
  #45  
Old 06-23-2019, 09:45:06 AM
Markoh Markoh is offline
Registered
 
Join Date: May 2019
Location: Lexington, South Carolina
Posts: 24
Thanks: 35
Thanked 3 Times in 3 Posts
Default Re: Sears ST12 Tecumseh Starter Difficulty Mystery and Carburetor Blow Back

Thank for your inputs on wire sizes and timing. I will will check size and watch video on timing.

With the carb removed and spark plug installed but disconnected the engine turn over difficulty is still there so I assume early ignition is not an issue.
Another thought is the spark doesn't initiate until after compression has begun. Obviously if engine doesn't turn far enough to where the spark is initiated, it cannot run. With that in mind, what are the dangers of using a drill motor to assist the starter to turn the engine over?
Since the drill probably doesn't have free wheel, if the engine does start, I'm thinking it could possibly spin the drill faster than I can remove it, break my wrist ( a la pre-starter model A's?) and beat the hell out of the drill and possibly me.

Shimmed valves to 0 clearance with Natural Lite beer can. Still have engine turn over difficulty.
I did learned I could hear the compressed air release out the exhaust when the exhaust valve begins to rise as I turn it slowly over by hand.

Also learned engine turns with little resistance through most of its cycle, then there is an initial resistance at what seems to be the beginning of compression, little less resistance, then difficulty of full compression. Don't know if that is useful info.

At this point I do believe the compression release is the issue so I read the maintenance manual and find only that it says the cam shaft with the compression release can be replaced and is available (1992 edition).
Do I have to break down the engine to access the compression release?
Reply With Quote
  #46  
Old 06-23-2019, 09:14:51 PM
Georgia SS Georgia SS is offline
Registered
 
Join Date: Jan 2012
Location: Nashville, Georgia
Posts: 82
Thanks: 2
Thanked 37 Times in 27 Posts
Default Re: Sears ST12 Tecumseh Starter Difficulty Mystery and Carburetor Blow Back

Hi
sorry the valve shims didn't work out, if you are going to pull the cam, it is ok to remove side cover and head with engine in the frame, i would have a replacement in hand first. The drill is a good idea if you could rig up a ratchet. In my former life i built racing go cart engines so i used a battery powered starter a lot, use it now to start onans and big briggs, not long ago i visited a race track to see the guys using battery drills for starters, need to be quick on removal. Why not put a an extra layer of can past 0 clearance to cause the ex valve to leak a bit, if the compression is as good as it seems the cyl. Will still have enough comp.to bust off.

Hang in there
jimmy
Reply With Quote
The Following User Says Thank You to Georgia SS For This Post:
  #47  
Old 06-23-2019, 09:25:09 PM
Markoh Markoh is offline
Registered
 
Join Date: May 2019
Location: Lexington, South Carolina
Posts: 24
Thanks: 35
Thanked 3 Times in 3 Posts
Default Re: Sears ST12 Tecumseh Starter Difficulty Mystery and Carburetor Blow Back

Good idea. Will put another .010 shim and give that a shot.
Will save a drill motor start as a last resort.
Reply With Quote
  #48  
Old 06-23-2019, 10:32:35 PM
Georgia SS Georgia SS is offline
Registered
 
Join Date: Jan 2012
Location: Nashville, Georgia
Posts: 82
Thanks: 2
Thanked 37 Times in 27 Posts
Default Re: Sears ST12 Tecumseh Starter Difficulty Mystery and Carburetor Blow Back

Hi
One more suggestion, there is go cart racers in your area, ask at the parts store or garage where one is at, i bet that bad boy will be glad to use his starter to start your motor up. Just tell him a Sox guy suggested him. will need socket to fit flywheel nut.
Greetings
Jimmy
Reply With Quote
The Following User Says Thank You to Georgia SS For This Post:
  #49  
Old 06-28-2019, 03:00:41 PM
Brian Lynch's Avatar
Brian Lynch Brian Lynch is offline
Subscriber
 
Join Date: Nov 2004
Location: Wellsville, New York, USA
Posts: 1,348
Thanks: 1,138
Thanked 1,216 Times in 477 Posts
Default Re: Sears ST12 Tecumseh Starter Difficulty Mystery and Carburetor Blow Back

If you tear into your HH120 to check the compression release here are some pics to compare yours to.
This came out of a HH120 that threw a rod.
Pic 1 shows the weight and spring that actuate the mechanism. Pic 2 shows the little cross pin that bumps the exh valve on the compression stroke.
As the engine speeds up, centrifugal force makes the weight move away and allows the cross pin stop to rotate out of place. This allows the cam to give the engine a full compression stroke.
Attached Thumbnails
Click image for larger version

Name:	P6280018.jpg
Views:	16
Size:	188.3 KB
ID:	338068   Click image for larger version

Name:	P6280020.jpg
Views:	14
Size:	215.4 KB
ID:	338069  
__________________
"May your walk through life have no dogpiles in it" -Brian Lynch
Reply With Quote
The Following User Says Thank You to Brian Lynch For This Post:
  #50  
Old 06-28-2019, 03:37:05 PM
Tracy T Tracy T is offline
Subscriber
 
Join Date: May 2009
Location: Cedarbluff, Virginia, USA
Posts: 3,098
Thanks: 979
Thanked 1,696 Times in 967 Posts
Default Re: Sears ST12 Tecumseh Starter Difficulty Mystery and Carburetor Blow Back

been following along, has anybody been into this engine before you got it? any evidence such as sealant, paint disturbed? i have taken the compression release completly out of engines before and never had this problem. I am thinking its time to tear down and inspect, sounds like camshaft timing is off to me.
Reply With Quote
The Following User Says Thank You to Tracy T For This Post:
  #51  
Old 06-29-2019, 01:12:02 AM
CharlieB CharlieB is offline
Registered
 
Join Date: Dec 2014
Location: Severn, Maryland, USA
Posts: 374
Thanks: 34
Thanked 185 Times in 140 Posts
Default Re: Sears ST12 Tecumseh Starter Difficulty Mystery and Carburetor Blow Back

Hooboy !!
Three weeks gone by. Markoh must be ready to throw the engine (and maybe us) into the river.

The compression reading of 80psi shows that the camshaft timing is correct. The starter motor is shot if it will not turn the engine over at that compression, even without a working compression release.

Speculation.....The flywheel removed easily because somebody already had it off, messed up the ignition timing, fried the starter windings trying to get the engine to fire up, then parked the tractor. ???? Might oughta check that spark timing before heading to the river.
Reply With Quote
The Following User Says Thank You to CharlieB For This Post:
  #52  
Old 06-29-2019, 09:59:51 AM
Tracy T Tracy T is offline
Subscriber
 
Join Date: May 2009
Location: Cedarbluff, Virginia, USA
Posts: 3,098
Thanks: 979
Thanked 1,696 Times in 967 Posts
Default Re: Sears ST12 Tecumseh Starter Difficulty Mystery and Carburetor Blow Back

not sure how you guys are coming up with ignition timing being that far off, only two things control the timing. point gap, and the flywheel key. unless i am missing something? I have suspected the starter very early on in this thread and pointed it out.
Reply With Quote
The Following User Says Thank You to Tracy T For This Post:
  #53  
Old 06-29-2019, 10:39:14 AM
Elevated Elevated is offline
Registered
 
Join Date: Jun 2019
Location: Bloomington, Indiana
Posts: 104
Thanks: 40
Thanked 73 Times in 45 Posts
Default Re: Sears ST12 Tecumseh Starter Difficulty Mystery and Carburetor Blow Back

Electronic ignition, no points. The air gap on the trigger pins is important, and he stated that the key wasn’t sheared. I won’t dismiss the starter being damaged, as people tend to hold the key in start when the engine rolls up against compression and stops, and that will cook it in short order. But I still think the original, root cause is the compression release. These engines are infamous for wearing the actuating pin down on the cam.
Reply With Quote
The Following User Says Thank You to Elevated For This Post:
  #54  
Old 06-29-2019, 10:59:51 AM
CharlieB CharlieB is offline
Registered
 
Join Date: Dec 2014
Location: Severn, Maryland, USA
Posts: 374
Thanks: 34
Thanked 185 Times in 140 Posts
Default Re: Sears ST12 Tecumseh Starter Difficulty Mystery and Carburetor Blow Back

Amen to the shot starter motor, and to the malfunctioning compression release.
Ignition timing may very well be correct, but that has not been checked.
You never know whose hands may have been in these old engines. The "electronic ignition" could be an improper replacement done as a previous repair/upgrade. Maybe not.....but a timing check seems indicated to rule that out.
Reply With Quote
The Following User Says Thank You to CharlieB For This Post:
  #55  
Old 06-29-2019, 11:38:36 AM
uglyblue66 uglyblue66 is offline
Subscriber
 
Join Date: Dec 2007
Location: Concord, North carolina
Posts: 5,210
Thanks: 2,340
Thanked 4,086 Times in 1,923 Posts
Default Re: Sears ST12 Tecumseh Starter Difficulty Mystery and Carburetor Blow Back

https://www.smokstak.com/forum/showthread.php?t=148084
https://www.smokstak.com/forum/showt...=114607&page=2
See if any of this helps you
Reply With Quote
The Following User Says Thank You to uglyblue66 For This Post:
  #56  
Old 06-29-2019, 04:55:45 PM
CharlieB CharlieB is offline
Registered
 
Join Date: Dec 2014
Location: Severn, Maryland, USA
Posts: 374
Thanks: 34
Thanked 185 Times in 140 Posts
Default Re: Sears ST12 Tecumseh Starter Difficulty Mystery and Carburetor Blow Back

https://www.amazon.com/Performance-T...DTHQ06PKRRNJPB
Reply With Quote
  #57  
Old 06-29-2019, 07:12:48 PM
uglyblue66 uglyblue66 is offline
Subscriber
 
Join Date: Dec 2007
Location: Concord, North carolina
Posts: 5,210
Thanks: 2,340
Thanked 4,086 Times in 1,923 Posts
Default Re: Sears ST12 Tecumseh Starter Difficulty Mystery and Carburetor Blow Back

Quote:
Originally Posted by CharlieB View Post
copy and paste,
The product is easy to use and durable
• The product is manufactured in Taiwan
• Easy installation
Reply With Quote
The Following User Says Thank You to uglyblue66 For This Post:
  #58  
Old 06-29-2019, 08:43:02 PM
CharlieB CharlieB is offline
Registered
 
Join Date: Dec 2014
Location: Severn, Maryland, USA
Posts: 374
Thanks: 34
Thanked 185 Times in 140 Posts
Default Re: Sears ST12 Tecumseh Starter Difficulty Mystery and Carburetor Blow Back

I got outsmarted by the computer.
The ratchet mechanism link in post #56 was supposed to be accompanied by a message that said, "Engines of this size can be started with one of these ratchets, socket wrench accessories, and a 1/2" drill. The socket wrench engages the big nut that holds the flywheel on." Prevents Model T kickback.
Reply With Quote
The Following 2 Users Say Thank You to CharlieB For This Post:
  #59  
Old 06-29-2019, 10:13:56 PM
keith1944 keith1944 is offline
Registered
 
Join Date: Nov 2008
Location: roseburg, oregon, usa
Posts: 44
Thanks: 3
Thanked 21 Times in 15 Posts
Default Re: Sears ST12 Tecumseh Starter Difficulty Mystery and Carburetor Blow Back

The starter is of the "permanent magnet" type and will lose the magnet charge over time. It'll spin the engine fine without the plug but won't have enough energy to spin it over against the compression.
Reply With Quote
The Following User Says Thank You to keith1944 For This Post:
  #60  
Old 07-20-2019, 12:45:41 PM
Markoh Markoh is offline
Registered
 
Join Date: May 2019
Location: Lexington, South Carolina
Posts: 24
Thanks: 35
Thanked 3 Times in 3 Posts
Default Re: Sears ST12 Tecumseh Starter Difficulty Mystery and Carburetor Blow Back

first - Thank you for all the inputs!
Second - I ain’t given up. See last sentence.
Georgia ss - Go kart starter that’s a great idea.
Brian - thank you for the information and the pictures. Very useful. Not quite visualizing how the compression release works. Do you know if the exh. valve rides on the pin when in compression release mode?
Tracy T - Fly wheel housing has definitely been removed. Paint on all other engine bolts appears to not be disturbed. Starter is still on my suspect list even though it looks new on the inside.
Charlie B - Thank you for that link! Looked a good bit and didn’t find anything like that. I Did attempt to turn the engine over with my Kobalt drill motor. No dice. Couldn’t hold onto it. Came close to hurting myself. Won’t try that again.
Spent most of morning looking for a Combination spark plug compression release. Apparently no one has designed one that works.
Uglyblue - thank you for the link. Looks like similar issues. Good info. especially if I tear the engine down.
Keith1944 - didn’t know starter was a permanent magnet type. I suppose a new starter is the only answer to a weak magnet.
With .027 shim in the exhaust valve, the engine did fire off for a second or two. Didn’t continue to run it because I didn’t want to burn the exhaust valve. Without a shop and proper tools I loath getting into the engine.
My next step is to get the engine to turn over safely

---------- Post added at 12:39:24 PM ---------- Previous post was at 12:31:41 PM ----------

Part of last post was not posted....
Next attempt is to get the engine to turn over -safely- using the starter and drill motor (with ratcheting adapter) at the same time. Hopefully, together they will overcome compression.
Thank you all again!

---------- Post added at 12:45:41 PM ---------- Previous post was at 12:39:24 PM ----------

Looking at go kart starters helps me realize I need a good way to hold the drill motor from torqueing my wrist.
Reply With Quote
Reply

Bookmarks


Thread Tools
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

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

F o r u m Jump

Similar Threads Chosen at Random
Thread Thread Starter F o r u m Replies Last Post
Cylinder oiler blow back problems boz Scale Model Engineering 2 09-08-2012 08:34:53 PM
Sears ST12 tractor Tecumesh engine richie25rich Garden Tractors and Mowers 3 04-10-2008 10:20:04 AM
Oiler pipe blow back Jesse Zilafro Hit & Miss Gas Engine Discussion 6 02-16-2007 12:26:25 PM
3 hp Mc Cormick M blow back in oiler? Lenn Antique Engine Archives 5 02-17-2004 10:24:19 PM
Oiler blow back! fixing the problem!! Adam Cottrill Antique Engine Archives 21 02-07-2002 02:00:25 AM


Use "Ctrl" mouse wheel to change screen size.
All times are GMT -4. The time now is 11:46:34 PM.

Smokstak and Enginads site search!


All use is subject to our TERMS OF SERVICE
SMOKSTAK® is a Registered Trade Mark - A Community of Antique Engine Enthusiasts
Copyright © 2000 - 2019 by Harry Matthews P.O. Box 5612 - Sarasota, FL 34277