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Donzo

vanguard ohv engine smokes

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Donzo
Just got a used 1994 Broadmoor w/ a 15 hp BS vanguard OH valve engine. Got off ebay in "as is " condition. I used it for the first time yesterday. It starts right up and doesn't smoke until I engage the mower, but then it smoked heavily. When I shut it off it back fired. I started it back up and let it warm up a while. No smoke when idling, but once I engage the mower PTO it started smoking again. What would cause this? How expensive a repair is it?

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RayS
I blew the head gasket on my kohler command and it used oil like crasy. Changed the head gaskets and it hasn`t used any oil between changes. If your head gasket or gaskets are blown it is possible that it was caused by the back firing when you shut it off. On my tractor the dealer told me when I shut it down to do so at 1/2 throttle to wide open throttle. I didn`t listen because I never did so with my cast iron single cylinder briggs engines. It would almost back fire every time that I shut it off at a idle. This was a costly mistake. I now shut it off like the dealer and the manual says to and it hasn`t back fired in the 2 1/2 years since I had it repaired.

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Al
Hi, This is what I expect you to find. I think the compression will check normal, a leak down check will be good. The crankcase vacuum will be normal UNTIL you put a fairly heavy load on the engine. When you load it down, the crankcase vacuum will drop to near zero or maybe even go positive. At this point there will be oil vapor blowing into the air cleaner base from the crankcase breather. The engine will really smoke until the load is removed and it will clear up. If the above symptoms are observed, and you pull the head, you will see a head gasket that looks normal except if you look closely, there will be a slight evidence of leakage from the cylinder to the oil return hole from the cylinder head. One other place you may observe leakage could be to the push rod area. These gaskets will not be blown, and under normal running don't leak enough to cause the problem. When a load is applied and the combustion pressures rise, they seep enough to reduce the crankcase vacuum and then the breather blows oil vapor into the carb causing the smoke. This a very common problem with these singles and the earlier V twins that had the steel head gaskets. I expect you will also find if you put a straight edge on the heads, you will find the heads are warped about .004 to .006 between the bolts. You can then take some 80 then 120 grit sandpaper and place it on a flat plate. Place the head on the sandpaper and slide across the paper being sure to keep the pressure as even as possible. Rotate the head 1/4 turn with each stroke. This keep the head surface flat. Continue until the sanding marks are showing on the head in the area between the bolts. Finish using 120 grit paper. It seems to me that the initial warpage from new sort of stresses or else stress relives the head casting. We have probably fixed 50 to 75 or more of these engines with this problem. Some only smoke when the mower hits some really tall grass. It seems like once the heads have been resurfaced they stay flat after the initial resurfacing. Clean the head bolt threads with a wire wheel and put some anti-sieze on the threads. Torque head bolts precisely as the Briggs manual instructs. Then feed her gas and grass. It will be interesting to me to see how close I am to correct on this tractor. Please let us know what you find. Al Eden

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Al
Hi, I think it is good news, as if I am correct, it is a relatively inexpensive fix parts wise. You will have some time in it, but if you do it yourself, not that much cash outlay. Feel free to ask anything in the line of help. Everyone here will be glad to answer what we can for you. I hope my post was not arrogant, it was not meant that way. I have seen a lot of these and this is what I think you will see. Sometimes it is kind of fun to see if you can score a hole in one. Al Eden

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dirtsaver
Al we see quite a few Briggs OHV Vanguards with this problem also. Somewhere around 30-40 of them a year. Briggs has not given us an answer as to why but your theory sure seem sound. By the way Al,next time you're coming through Louisville stop by and see our new dealership facility. We should be moved in by Saturday. Larry

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Al
Hi, I think the problem is related to the fact this engine is designed with only 4 head bolts. The bolts seem to warp the heads a little this reduces the clamping on the gasket. I have never been a big Tecumseh fan, but they did see the value of 5 head bolts in their twins. Al Eden

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Donzo
I didn't think you were being arrogant at all- so no worries. It is obvious you know what your talking about and I'm thankful that I was able to "pick your brain". That's why I posted the question. Thanks for the great advice.

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Donzo
I started taking the engine apart last night. I was surpised to see that it is only a single cylinder engine. The guy I bought it from said it was a twin. He also said he did a ring job on it and now I know he wasn't very truthful. Caveat Emptor. I only paid $225 so i'm not too upset. Other than the smoking engine and a noisy deck spindle, the tractor's in good shape. I think it is a warped head. The gap isn't uniform all the way around. Tonight I'll pull the head and see what I find.

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