Intek, 17 HP, uneven cranking speed

G

Gumby83

Well-Known Member
Hello to all and thanks for taking the time to read.

Model 311777
Type 0143-E1
Code 000914ZD

A customer brought in a Sabre 42” w/ this engine for a no start. I found the spark plug bore had been heli-coiled some time in the past, and the coil had been working its way into the cylinder over time. Only about 4 threads of contact on the end of the spark plug and pushing 10 PSI.

Customer thought on it for a day and asked us to repair, and if it runs then service/inspect mower, change oil & filters, and sharpen blades.

I used a threaded insert like this one, set it in red threadlock over night. This morning, I thoroughly cleaned the debris out of the cylinder using combinations of shop air and brake cleaner, then tried to start at full choke.

It took off almost immediately and ran very smoothly. I took it to a grassy area next to the shop, put the deck down and run the blades for 15 minutes to get everything warmed up good - the whole time the engine ran smoothly and responded surprisingly well to changes in speed and load - then return it to the shop for the oil change including fuel filter.

I had other repairs I was alternating on, so it sat for most of the afternoon before I started it since changing the oil and filters. I put 1 quart of oil in it before moving on to the other repairs, and that was just above the full mark with the dipstick fully seated - I was going to recheck after running it a few minutes.

I’m not sure this has much to do with it, but I did have to siphon the oil out of the dipstick tube because the drain plug is seized and it didn’t seem worth the time/effort to get it out because the engine had just run so well.

Now, it’s cranking unevenly like it’s out of time, and after 5-6 revolutions it snaps off a near-deafening backfire in the full choke position.

The plug is damp with fuel but not wet, so I don’t think it’s flooding to the point of hydro-lock.

Pulling the air filter and it’s obvious that pressure is escaping into the intake as well.

Valve clearances at TDC were:

Int. .005 (Adjusted to .004)
Exh. .002 (Adjusted to .005)

Cranking speed/consistency improved a little, but still no start and backfires in the full choke position. Any other speed and it just cranks but no backfire.

I haven’t yet checked compression, but will do so in the morning.

I’m at a loss for what could’ve happened.

Thanks.
 
Gumby83 said:
Hello to all and thanks for taking the time to read.

Model 311777
Type 0143-E1
Code 000914ZD

A customer brought in a Sabre 42” w/ this engine for a no start. I found the spark plug bore had been heli-coiled some time in the past, and the coil had been working its way into the cylinder over time. Only about 4 threads of contact on the end of the spark plug and pushing 10 PSI.

Customer thought on it for a day and asked us to repair, and if it runs then service/inspect mower, change oil & filters, and sharpen blades.

I used a threaded insert like this one, set it in red threadlock over night. This morning, I thoroughly cleaned the debris out of the cylinder using combinations of shop air and brake cleaner, then tried to start at full choke.

It took off almost immediately and ran very smoothly. I took it to a grassy area next to the shop, put the deck down and run the blades for 15 minutes to get everything warmed up good - the whole time the engine ran smoothly and responded surprisingly well to changes in speed and load - then return it to the shop for the oil change including fuel filter.

I had other repairs I was alternating on, so it sat for most of the afternoon before I started it since changing the oil and filters. I put 1 quart of oil in it before moving on to the other repairs, and that was just above the full mark with the dipstick fully seated - I was going to recheck after running it a few minutes.

I’m not sure this has much to do with it, but I did have to siphon the oil out of the dipstick tube because the drain plug is seized and it didn’t seem worth the time/effort to get it out because the engine had just run so well.

Now, it’s cranking unevenly like it’s out of time, and after 5-6 revolutions it snaps off a near-deafening backfire in the full choke position.

The plug is damp with fuel but not wet, so I don’t think it’s flooding to the point of hydro-lock.

Pulling the air filter and it’s obvious that pressure is escaping into the intake as well.

Valve clearances at TDC were:

Int. .005 (Adjusted to .004)
Exh. .002 (Adjusted to .005)

Cranking speed/consistency improved a little, but still no start and backfires in the full choke position. Any other speed and it just cranks but no backfire.

I haven’t yet checked compression, but will do so in the morning.

I’m at a loss for what could’ve happened.

Thanks.
Click to expand...
Few ideas:
1. Is the flywheel key sheared?
2. Carburetor mounted correctly and no air leaks?
3. Trash in the fuel system?


Usually a back fire is the timing is off. Is it possible the flywheel key is damaged?

Even a broken clock is right twice a day.

It worked and then it didn’t
 
Hello G.

Go back to the initial heli-coil repair and verify there are no problems there. If not, then move on. This may end up needing a head replacement, especially if a valve seat is coming loose after all these years. Stranger things have happened.

Customers often fail to mention some of the finer details regarding when it last ran.

An odd thought is a wrong or defective spark plug. Plugs do break the porcelain from time to time. Pull the plug and swap it but also check the coil firing with an adjustable gap spark tester. Do not trust a "Christmas" tree light design spark tester.

A flywheel key on a rider seldom shears unless someone has already had the flywheel off and did not properly torque it, no harm in pulling it apart enough to verify the key is still solid and not partially sheared. Don't overlook the ignition coil to flywheel air gap.

Trash in the fuel system and carburetor would be my next suspect due to the age of the rider. Grass clippings moisture a dirt collects over many years and settles in the bottom of the fuel tank. Once the rider is initially fired up, all seems well until the next start, them the gremlins come out.

One thing I have learned over many years of doing this work is to never trust an initial test run on any equipment. They will fail you usually when a customer comes to pick it up. A policy that I have is to run any machine like I own it for a couple of days. If it is going to act up, I want to catch it beforehand.

A Sabre model has not been made for quite a few years (1998-2001, the engine code indicates 2000).

TractorData.com - Sabre lawn tractors sorted by model

tractordata.com tractordata.com

Briggs and Stratton 311777 – Engine Specs

www.engine-specs.net www.engine-specs.net
 
Compression test is basically useless on an engine with an automatic compression release. Do a leak down test instead. And with this being an OHV engine disable the valve train and do a modified leak down test as to test the complete cylinder stroke.

This 2000 engine will have the easily sheared flywheel key and keyway. Also these engines are known for blowing the head gasket between the cylinder and the push rod galley.
 
I need to prioritize other repairs this morning but I did check the flywheel key and do a leak down test with the rockers completely loose at TDC.

It’s leaking into the crankcase but there’s no damage to cylinder wall that I can see with a bore scope.

Flywheel key looks good to me (see pic).
 

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Gumby83 said:
I need to prioritize other repairs this morning but I did check the flywheel key and do a leak down test with the rockers completely loose at TDC.

It’s leaking into the crankcase but there’s no damage to cylinder wall that I can see with a bore scope.

Flywheel key looks good to me (see pic).
Click to expand...
Key looks good,

Leaking into crankcase should be slight leakage past the rings and that would usually be expected, but if you loosen the oil fill cap and it blows the dipstick out under pressure, there is a blown head gasket at the push rod area between the block and the head. You can pull the valve cover to verify this.
 
I would replace the spark plug on the non-firing cylinder in case you got a defective one. It has happened to me. The backfire may have been exhaust flames from the other cylinder igniting the unburned fuel and air from the other cylinder.

I do not know whether the engine you have shares a carb venturi, or has a seperate venturi for each cylinder. If it has a seperate venturi, it is possible that one venturi has a partially plugged jet, and that the engine was partially relying on fuel in the oil to run. If so, then the mixture went lean when you replaced the oil.
 
Gumby83 said:
I put 1 quart of oil in it before moving on to the other repairs, and that was just above the full mark with the dipstick fully seated
Click to expand...
You would be wrong. Under the full mark, nope. Over full, nope. Right on full is a win. Check oil level prior to EVERY mow.
 
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