Tecumseh starter rope pull back

[creia]

I recently took an old 8 HP Tecumseh L -head into inventory HM80-155042A
I am just starting to go through it to see what it needs. The first thing I noticed is that when pulling on the starter recoil rope to try to start it, the rope (generally) very violently pulls back and rips the grip out of my hand. Is this most likely a valve adjustment issue or an ignition timing issue?
Thank as always.
Michael

[KE4AVB]

Experience has taught me that it can be a partially sheared flywheel key or a bad camshaft (compression relief). Hopefully it is a flywheel key as the camshaft is listed as NLA on two my trusted parts suppliers outside my distributor which doesn't even find PN other than the parts lookup.

[Skywatcher]

Hi Creia

Parts Tree says this engine has breaker points and condenser under the flywheel. Generally speaking, when the valves go out of adjustment on an L-head engine, valve clearances usually decrease leading to loss of compression as the valves don't seat properly. I would start with a compression test to get an idea if the compression relief is working or not. Next, I'd pull the flywheel, clean and check the breaker points, adjust if necessary. The tech manual says .020" gap on the points, setting them to .016" to .018" will retard the spark very slightly for easier starting. It is also possible that the magneto has been messed with at sometime in the past thus throwing the timing off. Check the flywheel key while flywheel is off.

Parts Tree says the camshaft for this engine is P/N 33366. A few years ago, I did a re-power on a snow blower. The Tecumseh short block came with the standard length camshaft, but the engine on the snow blower had the extended shaft for the track drive. I ended up drilling out the crankcase cover, drilling an oil drain back hole and installing a seal so the camshaft from the old engine could be used. Therefore, I have a brand new camshaft for an 8 hp. Tecumseh engine, but I'd have to do some research to find the correct P/N for the shaft I have. I thought it was 33375, but that number appears to be a blower housing according to Parts Tree. Let us know what you find and we'll go from there. All the best,

Sky

[Arkie]

Tecumsehs that are slightly out of time will rip meat off your fingers, especially the 8-10hp's.

If that one has the adjustable magneto coil for timing and is the L-head see pg 68-70 of the FREE Tecumseh 3-11hp L-head service manual for timing.
Check the specs section in the rear of the manual for CORRECT timing specs and in the manual and BE SURE YOU ARE ON THE CORRECT PAGE AND ENGINE. Some of the engines had a serial number breakover for different timing specs and if you get on the wrong serial number range for timing you will be SOL.
The timing is very critical to prevent or reduce the pullback and if the timing is too far BTDC they will usually throw a rod (especially if you hear the ping or spark knock when the engine is rev'ed up) and if too far ATDC they will start harder and not as much power. NOT getting the timing correct on the old points type Tecumsehs is one of the MAJOR reasons of them getting a bad rap from shade tree mechanics.
If you do not have the special Tecumseh timing tool you can remove the head and set a dial indicator on the top of the cylinder to get the CORRECT piston TDC/BTDC reading. The top of the piston is not right below the spark plug hole and the special Tecumseh timing tool needs the has a offset leg. I usually just bolt the head back on with the old head gasket as a preliminary run timing test if the old gasket appears ok and if good engine timing run I might replace the gasket later. I've re-used the old OEM gaskets with good success for my own eq, but the later type gaskets not so much.

On some of my very old Briggs rope crank engines that pull back hard due to worn camshaft and the engine is a good runner once started and parts are high or NLA I've done a REDNECK mod and installed with good results manual compression release valve in the top of the head. (chainsaw type compression release valves)

T-Man from the old Perr forums helped me get better acquainted with the TECUMSEHS.

[creia]

Thank you very much for the replies. All good information and duly noted. I'll be going through the engine in the coming weeks and I will report back with my findings.As far as doing a "traditional" compression test (i.e., using a gauge and repeatedly pulling on the rope start) I doubt I'll be able to do that due to the jerk backing of the pull start.The engine does have spark and "seems" to have decent compression (maybe too much?).

I'll be checking both the valves and timing and adjusting as/if needed. Agreed on the Tecumseh timing being tricky. In the last 15 years, I think I have had to set the timing on maybe 2 or 3 and it is always seems to be a challenge for this "garage-hack" small engine mechanic. (I have the L-Head manual and a dial indicator) Please refresh my memory- (At 68 years old probably not much left) - Can just the the points be replaced w/o screwing up the timing and having to reset it?

The take away I am getting from your replies is that it is more likely the timing being off or the compression release not working rather than improperly adjusted valves causing the starter cord pull back?
Michael

[bgsengine]

Thank you very much for the replies. All good information and duly noted. I'll be going through the engine in the coming weeks and I will report back with my findings.As far as doing a "traditional" compression test (i.e., using a gauge and repeatedly pulling on the rope start) I doubt I'll be able to do that due to the jerk backing of the pull start.

If that happens when you are doing a COMPRESSION TEST, then the problem definitely ain't timing.. so if you don't get kickback then (or with spark plug wire unhooked) , chances are it IS ignition timing..

The engine does have spark and "seems" to have decent compression (maybe too much?).

I'll be checking both the valves and timing and adjusting as/if needed. Agreed on the Tecumseh timing being tricky. In the last 15 years, I think I have had to set the timing on maybe 2 or 3 and it is always seems to be a challenge for this "garage-hack" small engine mechanic. (I have the L-Head manual and a dial indicator) Please refresh my memory- (At 68 years old probably not much left) - Can just the the points be replaced w/o screwing up the timing and having to reset it?

Correct - as long as you do not loosen the 2 bolts holding the stator plate (which is also the breaker box, and holds the points inside) then your timing should not change (and if you wanna tweak timing, simply adjust gap a little more or less than .020)

The take away I am getting from your replies is that it is more likely the timing being off or the compression release not working rather than improperly adjusted valves causing the starter cord pull back?
Michael

Quick test - crank engine over with plug installed, but spark plug wire OFF.. If there's no spark to ignite the gas, you should not see kickback... so if you do get kickback, it's probably something mechanical.. if not, then it is probably ignition .. simple.

[Arkie]

First thing to do is make sure the points gap is correct and very close to correct and the spark plug is the correct one a gapped at specs and then if still kicks back you will need to see if you can find the timing specs in the manual FOR THAT SERIAL NUMBER ENGINE. After you have found the correct and specs and if you do not have the Tecumseh tool I've had to remove the head, use my DIAL indicator bring the piston up to TDC, AERO out the dial indicator then rotate the piston to proper specs and see if the properly gapped points are indication properly and if not the mag screws have to be loosened and the mag rotated until the timing is correct. (and this usually take few hits and misses and will change sometimes as the mag screws are secured.
I've tried to rig up a redneck thru the spark plug hole offset way of monitoring the piston movement but never could get it done and did not want to spend the $70 when the tool was available. It does not do any good to put witness marks on the mag legs/screws and then reset to the same place after a Mag has been off or moved because it's so critical that it will get out of time enough to kick back when you try such.
Also I usually drill and tap the flywheel on my own Tecumsehs so as I do not have to constantly use the Whack and pry to remove the flywheel, especially when one is out of time.
Constant go backs is not a good thing with the whack to remove method. Also you might look into the flywheel key on yours, I seem to remember that some of the Tecumsehs used a slight offset flywheel key. (and it only was to be installed with one end in the proper direction on the keyway. (and some of the standard keys had a offset notched end to be installed in one direction in the crank keyway slot) I have not been to the m&d mower.com site in awhile, but they had a very good Tecumseh reference LONG list by model and serial and showed pictures of parts/part numbers. If they still have such look on the right side long list a scroll down to Tecumseh or maybe even Peerless Tecumseh and then look for the long scroll list for Tecumseh engines. m&d handled lots of NLA Tecumseh parts, but after getting the proper Tecumseh part number I could sometimes find the parts other places like flea bay for example. Some of the old Model Tecumsehs with points did not have a compression release, they just relied on correct timing of the engine
The later Model electronic ignition ign type Tecumsehs had a compression release built into the cam shaft and the 8hp and up were not user friendly to hand crank when cold and the compression release give lots of complaints. (and if had low emission type Al Gore carbs would hunt and surge and hunt severely when cold or when sucking cold air)
Lots of Tecumsehs in the 8 hp and up were built with and needed the electric start, especially during cold weather
If I heard complaints of a Briggs or other brand engine having complaints of surging and hunting I would just tell them to rename it Tecumseh and it will then be ok.

If someone else has ever loosened and retightened or moved the magneto in yours or gapped the points wrong it WILL BE OUT OF TIME.
At one time I found quite a few 8-11hp electric start parts for the old Tecumsehs and converted them to electric start if the engine block was tapped for the starter. Most Tecumseh snow throwers used 120v starters.

Do check and make sure yours has the proper flywheel key.

[Arkie]

I failed to mention what bsengine wrote;


You should test this first. I've seen some of the old Model Tecumsehs, especially the H series 8-10 hp Tecumsehs that have serious pull thru WITHOUT having any spark. (and I seem to think some of the old ones did not have any provision built in for any type compression release) Just built for the tougher guys to yank on. Them type Tecumsehs 8-10hp hard to rope crank really come alive with electric crank and I keep a eye open for the old electric crank type Tecumsehs for parts, even seen some of the old iron 8 hp tiller engines that are both rope and electric crank with charging stators and weigh twice as much as a late model aluminum block engine.

Some of the OLD Model Briggs especially the H shafts 8hp and up had the now obsolete and NLA camshaft ground for compression release and parts expensive if found. This is the type that I have installed the manual compression release in the head with good results if it is an otherwise good engine.
But HF $100 predator engines are usually what people now days go to to save few big bucks for tiller and Wood splitter engines. They can go through 3 or 4 of the Predators as compared to the cost of a new name brand GOOD engine such as Brigg's, Honda or Kohler. I cannot seem to get tools or most any eq that is China made to live very long around me and not surprised about such when it breaks.
I know that you are usually re-storing vintage engines keeping them original as possible for vintage collector eq, etc. (and I try to do the same for my own use when within reason)

[Skywatcher]

Hi Again Creia

On some of these older engines, sometimes the only thing to do is to Tailor your pull to make the most of flywheel momentum. Pull the engine over slowly until you feel the piston go to TDC on the compression stroke. Now reset the starter cord and give a firm brisk pull. This will give you about 1¾ revolutions of the flywheel before the piston meets compression which is often enough to get a single cylinder engine started. Yes, you'll be pulling against a vacuum above the piston for the first ½ a revolution, but this equates to about 10 to13 psi (atmospheric pressure) against the underside of the piston which disappears as soon as the exhaust valve opens.

Non mechanically minded people seem to have a hard time grasping this concept. However, with your experience, I'm sure you'll understand the theory behind this technique. All the best,

Sky

[KE4AVB]

Same technique is used for starting compression 2 cycle chainsaw except you only get +-3/4 turn before you back up against the high compression. This where speed is you friend as you got to pull hard and fast to start these saws. To develop the speed sometime I need to both pull the rope and push the saw away for the extra speed.