# Briggs & Stratton Low Compression?



## ironman_jk (Jul 7, 2016)

I'm can't seem to figure out what is wrong with my lawn mower. It is a Toro Recycler 20041 with a Briggs and Stratton 125K05-0186-E1. A few weeks ago I performed an annual tune-up. Frustrated with it's performance while mowing tall grass I decided to speed up the RPM's for about 25 minutes. A week later I went to start it, and it was barely running. Sounded like 1 rev/sec. I happened to notice a few drops of oil under the spark plug. A compression test showed 40 psi. I figured the head gasket was blown. I pulled off the head, and the gasket looked fine. With engine back together I performed a leakdown test. I heard lots of noise in the crankcase and a little from the exhaust. I disassembled the engine enough to install new rings and lapped the valves. Upon reassembly (with a new head gasket) I performed another leakdown test. No noise from either valve, however, I still hear noise from the crankcase. A compression test now shows 60 psi. I can get it to start, but it runs at low RPMs and dies after about a minute. Can anyone help me figure this out? I appreciate any input.


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## AVB (Nov 28, 2014)

A couple things here.

First you can't just slap in another rings without at deglazing. Second if the cylinder is worn then deglazing usually just makes it worse even if the compression reading goes up some as if the cylinder is oval-ed deglazing just makes the oval larger. The real way to correct this is to use a ridge hone, oversize, then install new oversized piston and rings.

Also on these small L-heads tend to warp causing problem but if you only hearing air escaping into crankcase then most likely the rings are sealing.


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## ironman_jk (Jul 7, 2016)

I was second guessing my decision not to deglaze. I didn't deglaze because the cylinder walls and piston looked really good. If I were to just deglaze the cylinder walls, would I need oversized rings or could I use the stock size? And, how long does it take for piston rings to seat? Any chance that is the issue? Also, why would it run for a minute before dying? Could there be another issue I am overlooking that is causing it not to run and let the rings seat?


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## AVB (Nov 28, 2014)

The cylinder would need to be mic at three level with reading at 90 degrees of each other at each level to out the cylinder condition. Your particular engine the standard cylinder diameter is 2.6875 with anything over .005 requiring going to .020 oversize. If you don't have a ridge hone or access to one just leave it alone as a flex hone won't work except for de-glazing.

As for the dying check for a fuel restriction such as swollen needle seat. But I think part your problem is still the low compression.


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## ironman_jk (Jul 7, 2016)

I am familiar with a flex hone, but I can't find a ridge hone. Are you talking about a ridge reamer or a cylinder hone with the three stones or something different?


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## AVB (Nov 28, 2014)

It is a two stone with two wipers setup. I'm use a Lisle 15000 and 16000 series hone with 180 grit stones for aluminum.

Here is a link to the Lisle 16000 hone. They can be found on Amazon for about $140 depending your account with them. You will also need 1/2" low variable speed drill. 0-500 rpm which for your size cylinder you be running at around 250 rpm max or you will gall the cylinder walls. The drill can be found at Harbor Freight Tools.

Lisle Corporation


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