stihl br600 blower

cranheimDecember 16, 2011

I have been using my STIHL BR600 Backpack blower for over 4 years. I put on about 100 hours per year doing yard work on three large properties. I had been checking the valve clearances and de-coking the engine once a year using the STIHL De-Coking fluid. Everything went fine until my last valve inspection and decoke. After the decoke, the engine ran fine for about 20 minutes, and then stopped like it ran out of gas. When I tried to start it, it had no compression. I removed the valve cover and checked to make sure the valves were working correctly, and the piston was going up and down normally. I took it to a STIHL dealer and he felt the loss of compression while feeling the valve operation as I did. He said everything looked and felt normal, but there was a possibility one of the valves may have chipped. It would cost 200 to 250 dollars to take it apart and replace a valve, or $350 for a new engine. I took the machine back home and decided to look at it more carefully. At first I tried blowing compressed air into the spark plug hole while the valves were closed and the piston at TDC ready for the power stroke to see if I could detect where the air leak was. All that did was drive the piston down with great force. I then decided to recheck the valve clearance again, even though it was fine right before the failure. Much to my surprise, the exhaust valve clearance was a little more than normal. I can't tell you the exact setting because a normal feeler gauge cannot be used. I can only use the special STIHL gauge with the narrow end to verify the correct setting. It now became apparent that the valve was not fully seated. I blew some SEA Foam in the spark plug hole, turned the engine over a few times, and let it sit for 30 minutes. I then put compressed air in the spark plug hole while tapping on the exhaust valve rocker to snap it open and closed. I replaced the spark plug and found the compression and valve clearance was back to normal. I can only assume there was a partical of carbon from the decoke procedure that got caught in the valve seat. The thing that surprised me about this is that the increased valve clearance was too small to feel by hand, both by myself and the STIHL tech, but still caused this loss of compression.

The main lesson I learned from this is to always check the valve clearance with the correct gauge if you suddenly feel a loss of compression.

I called STIHL tech support about this carbon issue, and the need to decoke using STIHL Ultra synthetic oil. I was told as long as I use the synthetic oil, and fresh 89 Octane fuel, I should not have to decoke the engine as part of normal maintenance. I used a blend of ECHO oil for the first year, because the Ultra oil was not available yet. Now, my dealer only carries the STIHL Ultra oil.

Again, I am well pleased with my BR600 and would recommed it to anyone.

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ewalk

"C" Great story , I also have changed my oil usage to syn based oils over the last few yrs. I remember having to decarbonize pistions and rings back in the day while racing in various events (Snowmobile and Motocross). The oil technolgy for 2-strokes and event 4-strokes certainly has evolved too what was the norm just decades ago . I even use modern oils within older vintage units calling for much heavier mixtures with no concerns due to the advances in todays superior synthetic oils. Just a further note on decarboning requirements , we even utilized fine spray of water within Diesels using a spray bottle and misting the intake of various units while they were running to carefully reduce carbon buildup between overhauls . Anyhow Thanks again for sharing your very concise trouble shooting of your valve bridging issue . Nice to see you save a lot of additional expense with a little time & patience ! Have a Great New Year Dude !

    Bookmark   December 31, 2011 at 10:09AM
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newjerseybt(5b NE PA)

I am no expert but have heard of this happening when valve clearances have gotten tighter because of valve seat wear over time. The engine heats up lengthening the valve stems until a valve does not close properly and compression is lost. When the engine cools, the engine will then start. On some type of engines I heard an easy cheap remedy is to machine a number of thousandths off the stem to restore proper clearance. On others there may be a manual valve adjustment (nut). There may other fixes that I am unaware of depending on the design of the engine. I leave that for the experts to explain.

    Bookmark   January 2, 2012 at 8:54PM
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