fresh rebuild is blowing head gaskets, help!

[Shrek 12]

Here's the background. I bought a C-85 last year with a Kohler K181 engine. Mowed all season with it while planning a rebuild over the winter because it was burning oil. I found another k181 that I rebuilt this winter.  I also plowed snow this winter while rebuilding the replacement motor.  The replacement motor was bored .010" over and received a valve job and new exhaust valve.  Installed rebuilt motor and used carb, exhaust and ignition from the original.  About 30 minutes into the first mow I heard what I thought was a rattle.  A few minutes later the engine bogged then the cylinder head gasket blew with a pop. I replaced the head gasket. After about 40 minutes of mowing I started hearing a rattle. Then again, a few minutes later the engine bogged and the cylinder head gasket blew.  I now think the rattle was possibly pre-detonation that led to the cylinder head gasket failing.  The spark plug tip looks tan.  Any thoughts on what's causing this?

 

Matt

[OutdoorEnvy 1,522]

The first thing I would check is the valve clearances.  You could also compression test it to confirm.  It might be one isn't opening at the right time and it's building too much pressure.

[ebinmaine 67,623]

I'm going to throw a couple things in here and then wait to see what the other people say anyhow.

 

Is the points Gap set correctly and staying in place? Like are the points tightened correctly?

 

The first thing that actually popped into my head was wondering about the crankshaft keyway...

[ebinmaine 67,623]

Just now, OutdoorEnvy said:

The first thing I would check is the valve clearances.  You could also compression test it to confirm.  It might be one isn't opening at the right time and it's building too much pressure.

Can't do a compression test on a Kohler but you can do a leak down test.

 

Valve theory does make sense though. Once it gets hot things would change.

[WHX?? 48,828]

Check the head for flatness and glass if not too far out of flat Shrek. If your not sure how let us know and we'll walk you through it or there are many good you tubes on doing it. Next make sure block threads are good and chase them as required. Use new head bolts, I use flanged grade 8's. Lube the bolts when installing.  Quality head gaskets, some purists like to use genuine Kohler but I just use Stens or after market with no problems. 

Torque per the manual and recheck after a bit of run time and while engine is still hot. 

 

Any chance the the crank to cam timing a tooth off? It's an easy one to goof up on. 

[squonk 41,155]

Tan plug. Running lean? Burning the gasket? Timing way advanced.  Exhaust valve not opening all the way. Pretty much what everyone else has suggested.

[Shrek 12]

Valve clearances were checked during assembly and after engine was installed.

Point gap and spark plug gap were checked before startup.  I'll check the point gap again.

Head was sanded flat and checked with .003" feeler gauge.

I did not put in new head bolts. I did lube them prior to install though.

The crankshaft keyway is in good shape.

 

I'll check the point gap again.  I was careful to line up the timing marks when installing the crank.  Is there a way to check the ignition timing statically?

[Shrek 12]

1 hour ago, WHX24 said:

 

Any chance the the crank to cam timing a tooth off? It's an easy one to goof up on. 

Has anyone experienced this?  would an engine behave like this with timing off by a tooth?

[squonk 41,155]

The only things that would cause repeated gasket failures are warped head and or excessive heat. You got the head covered. Excessive heat is caused by timing and or lean mixture. If your cam timing is off, you're ignition timing will be off. It won't matter where the gap is set. You can try taking out the plug. rotate the engine to top dead center. Also take off the points cover. Just as the piston reaches TDC the points should start to open. If they open way before the ignition timing is way early which will cause pinging and rattling. If it doesn't start to open until you go past TDC it's way late. Either one is bad. If you cannot correct this with a points adjustment, your cam timing is off. You may be able to tell with the head off. Rotate the crank and watch the valves. There is some over lap between the exhaust closing and the intake opening. If the piston is a quarter of the way down and the exhaust is still partially open you cam is probably off which puts the ignition timing off. 

 

Another tell tale sign is run the engine in the dark. If the exhaust starts glowing fuel mixture and valve / ignition timing need to be looked at.

Edited April 26, 2021 by squonk

[WHX?? 48,828]

From a manual ... should help nail down if it's a timing issue.  I have the whole manual if that helps any further Matt. 

Edited April 26, 2021 by WHX24

[Shrek 12]

1 hour ago, WHX24 said:

From a manual ... should help nail down if it's a timing issue.  I have the whole manual if that helps any further Matt. 

That could be helpful. I'm looking at the old bearing plate and flywheel.  The only "sight hole"  would be the V-shaped notch where the starter sits.  On the flywheel I see what looks like a part number and possibly a single mark like a " | " on the back side below the teeth.  Does any of this sound correct?

[Achto 27,604]

3 hours ago, WHX24 said:

Quality head gaskets, some purists like to use genuine Kohler but I just use Stens or after market with no problems.

 

One thing that I look for on a head gasket is weather or not it has a fire ring on it. By fire ring I'm referring to the metal edge on the inside of the gasket. All OEM Kohler and some aftermarkets will have this feature. I believe that the fire ring supply's better sealing power as well as protection from the heat and compression. 

 

This OEM gasket has the fire ring that I am talking about.

 

This aftermarket one does not have the fire ring.

[squonk 41,155]

5 minutes ago, Shrek said:

That could be helpful. I'm looking at the old bearing plate and flywheel.  The only "sight hole"  would be the V-shaped notch where the starter sits.  On the flywheel I see what looks like a part number and possibly a single mark like a " | " on the back side below the teeth.  Does any of this sound correct?

That manual is for the older engines. Look for a hole in the engine shroud beneath the coil towards the bottom. The flywheel will have a S and a T. They are hard to see.

[Achto 27,604]

5 minutes ago, Shrek said:

The only "sight hole"  would be the V-shaped notch where the starter sits.

 

There should be a round hole in the back of the aluminum bearing plate. It may have a metal plug in it that will have to be removed to see the timing marks.

[WHX?? 48,828]

25 minutes ago, squonk said:

Look for a hole in the engine shroud beneath the coil towards the bottom.

Thought that was only for big blocks? Either location there should be a hole for viewing the timing marks. 

[Gregor 4,846]

I recently rebuilt a K181. It started, ran fine on medium to high RPM, but would not idle well. I checked lots of things. Turns out, I had the timing mark off by one tooth on the cam and crankshaft. It's easier to do than you think. I reset the timing marks, runs perfect now.

[Shrek 12]

I don't see a timing hole.  I have the cylinder head off and have checked the cylinder position when the points open using a test light. They open before TDC and there is about 1/8" of travel ( actually 0.1" from the caliper) of the cylinder up before it reaches TDC. I could slap together the old engine parts to get a comparison measurement.  I would really want a strong indication that the timing is off before tearing it all apart.  The cylinder head gaskets come from Isavetractors and do not have a fire ring.

[squonk 41,155]

I just looked at some pictures of a Kohler OEM 8 HP head gasket #41-041-10. No fire ring on them.

[Gregor 4,846]

Do this. This is how I discovered my timing marks were off. If yours checks out OK, you are good to go. I have only rebuilt 3 Kohlers, but all my parts came from isavetractors. No problems yet.

 

P.S. I just love the sound at the beginning of his videos.

 

BTW  Your timing marks may or may not be, where they show in this video.

Edited April 26, 2021 by Gregor

[Shrek 12]

56 minutes ago, Gregor said:

Do this. This is how I discovered my timing marks were off. If yours checks out OK, you are good to go. I have only rebuilt 3 Kohlers, but all my parts came from isavetractors. No problems yet.

 

P.S. I just love the sound at the beginning of his videos.

 

Your timing marks may or may not be, where they show in this video.

Okay. I have found the sight hole in the housing, the mark on the bearing plate, and the "S" on the flywheel. I'll follow through with the video instructions and report back.

[Shrek 12]

I set the points gap per the video. It appears that the cam and crank gears are indexed right.

[Gregor 4,846]

Kohler k-181  Spec # 30108

 

 

Kohler K-181. Spec # unknown.

 

[ol550 830]

Hurry up and get this figured out. I've got a 12 horse with very similar problem.  First out the door after a rebuild, mowed about 30 min and started rattling, Idled down for a few min and started mowing didn't last long.  Blew a hole in the head as well as cracks.  That was last fall, got it out for the first time this spring after about 30 min rattling again and head gasket leaking.

I'm thinking the bore job is too tight.  

[Gregor 4,846]

3 minutes ago, ol550 said:

I'm thinking the bore job is too tight.

Maybe rings expanding after warm up?

[ol550 830]

25 minutes ago, Gregor said:

Maybe rings expanding after warm up?

 

One thing I did notice each time is the smell of hot oil and fumes from the crankcase vent.