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ZippoVarga

Briggs 18hp Twin Q and A(Problem Solved)

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ZippoVarga
Howdy snow capped north east and all other fellow Simpletons!! (That didnt sound good) :D:D I recently had a discussion with Al over a situation with a certain 18hp twin Briggs of the early 1990's vintage and we thought it would be a good technical entry to the sight.....so here goes! Symptoms: Hard cold starts, as though the starter has a dead spot or the valves are not releasing pressure to allow for proper starting. Possible problems as stated by Al 1. Cam lobe which is designed to release pressure on start up is worn. 2. Tappet which lifts valve is worn. 3. Insufficient ground, corroded wires. I should also add that once this engine does start, all further starts through out the same day are trouble free. I can heat up the engine with the sun for a couple hours and it starts as normal. What else would any of you attribute to this problem and what would you propose to do for a cure in each of the affore mentioned potential problem areas. I have discussed this with Al but thought I would get every one elses thoughts and possible solutions. Once I find the culprit I will re-post my findings as to help others who experience a similar problem in the future. Sean aka Zippo

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D-17_Dave
I would tend to think the electrical connections are weak. It takes a lot more amps to start a cold engine. Other than that with respect to the hard spot you refered to, are you sure it isn't hydro locking a cyl. Once you heat it up a bit it could vaporise a small amount of fuel built up in a cyl. and start OK. Pulling the plugs when it's cold and spinning it should help determine if this is any issue. My thoughts are still leaning towards weal connections. These could be at the bat, sol, or bad cable ends. Does putting jumper cables straight to the starter make any diff?

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firefoxz1
My first quess would be a sulfated battery. second would be gruded? valve guides/lifters. I found bad grounds show up more when warm not cold and the current draw more because of greater compression on a warm engine, but this is on cars not small engines. All in all I say my quesses or just that.

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ZippoVarga
Update....I replaced the starter with a well known good starter. To no avail. Then I put a 650 cca deep cycle directly to the starter. Again, same result. So, now we're digging a little deeper into the problem. Dave...I removed both of the plugs and gave the engine about 10 seconds of free spin. Replaced the plugs and still the same situation. Now comes the more in depth diagnosis. How do I determine if the lobes on the cam or the tappets are not lifting the valves for adequate pressure relief to allow this engine to spin as originally designed. Assumation is to remove the crank case breather assemblies and check the gap right? What should the proper gap be before tearing into the engine to check the lobes on the cam. I may add.....this "condition" was not gradual. One day the engine fired fine, the next it wouldnt turn over as it should. Sean aka Zippo

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ZippoVarga
Firefox, 70 dollars later for a wet cell battery disproved a sulfated battery. All the wiring is as healthy as the day the tractor was new. I am leaning towards your second suggestion that it's the guides or lifters in relation to a small engine. Has any one thought of gummed up valves? Could this cause such a result? With these high compression, air cooled engines you also have to factor in heat expansion don't you? As was mentioned by Al in our conversations, this would explain the easy starts once the block is warmed up. So it could be just a couple sticky valves right? What do you small engine motor heads use to REALLY lubricate up a sluggish engine? Lucas? Rizlone? Marvel Mystery Oil? I'm looking for an IN DEPTH discussion about how all of you have solved big AND small engine troubles so that this will be a worth while post for people to reference later on down the line. Hope to hear some great back yard solutions as well as the professional directives to fixing this ailment. Sean aka Zippo

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D-17_Dave
If removeing the plugs limbered up the engine spinning it over without noticeing any hard spot or turning it over by hand would elliminate any valve build up or sticking problem. If nothing came out of the plug holes then thta would rule out liquid building up from gas leaking into the cyl's possibly causeing a hydro lock. Now you must get more indepth with the electrical system. I'd measure the voltage at the input of the sol. while cranking and the output. Under this cranking load the voltage should be the same. If not you have a bad sol. easure the voltage at the bat and at the starter, voltage should be close to the same there also. If not check back through the system to find the weak component. No matter how good and strong a bat. is if you can't get the amperage to the starter it won't work correctly. If you have a good bat and the voltage drops all the way back to the bat. and it's a significant drop then the starter is pulling to much load and is converting all the amperage into heat instead of mechanical energy to turn. A note on some components, just because a starter will start one engine is no gaurantee of it being good. It can be new and still be defective.You didn't answer whether or not bypassing the entire electrical system with jumper cables made any differance or not. This would help to identify whether it's an electrical problem or insside the engine. If your sure it's engine and not electrical, and the engine spins easily by hand then I'll ask does this engine have points or electronic ign.?? I think I remeber them haveing points. If t's been converted with magnatron or a aftermarket box then there would be another source to check. Early ign. could be all that's occuring. Boy my fingers are tired now.:o):D

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Al
Dave, He has a new starter and my first suggestion was to take jumper cables from his car and go from the starter itself to a solid ground on the engine block. Don't think he brought all of these details when he said he tried jumping it to the starter. This should eliminate the whole tractor electrical system by substituting a high current primary system. I am not disagreeing with you, just wanted to clarify a clue. Our first check would be to measure the voltage across the battery when trying to crank and then at the starter and the engine block to check the total loss in the pos and neg primary circuits. One needs to heep in mind that at stall torque the current is extremelyy high and can pull those small batteries down significantly. I think my next step would me to check the compression cold and if it is above 75 lbs, would remove the covers to the valve chambers and check the valve clearance. We are seeing a ton of the new OHV single cyl Briggs with the same symptoms not engough starter torque,(just did a warranty on a brand new one for Wal-Mart the other day,set tappets and fixed it) and it is usually loose tappets. One with a bad camshaft. If the compression is above 75 to 80 lbs on a flathead, I would look for compression release problems. Starting with valve clearance. If the valves are barely touching the decompression bump, as soon as it runs or warms up the thermal expansion of the valves and stems, may be enough for the comp release to kind of work. My thoughts, and they are free, value accordingly. Al Eden

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ZippoVarga
Thanks Al, I did forget to mention that I put a 650cca deep cycle directly to the starter and a good ground and had the same results. So, we're at the mechanical point with this engine. How do I fix loose tappets should this be the culprit? And what's the correct valve clearance supposed to be? If the clearance is not correct then how do i correct it? I seem to remember a post about filing the valve end or something of that nature. With a seasonal mower which sits idle 8 months out of the year and is approximately 13 years old one wouldnt think that wear would be a factor but with Al's recent repair on a new engine with a similar problem I will not rule anything out at this point. Does it make sense that it is the tappets since this problem came about so suddenly? Here's another added bit of information.....one side measures approximately 70 lbs and the other side measures 80+ pounds of compression. I am planning to remove the heads and inspect the clearance tomorrow evening and I will post those results at that time. Thanks for joining in the post Al!! I forgot to e-mail the post topic to you. Glad you found it!! Sean aka Zippo

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ZippoVarga
The end........What wound up being wrong? A severe build up of carbon in the combustion chambers. I removed the heads to find a LOT of carbon build up. Mostly due to a rich burning condition caused by the air filter being bad. To tell the truth on this particular tractor.....I have neglected it. Why?? It's a Ranch King by MTD. As though that's not enough said......It's not for lack of working on the thing because it requires more of my time repairing inferior parts than any of my other tractors combined. Where I went wrong was neglecting the one part of the tractor that's worthy. The 18hp briggs twin. Well...This was my mothers primary mowing machine. I've since converted her ^ so it left time for me to get the engine in shape for a transplant and to scrap the rest of the mower. I know I know. I should have kept better tabs on the B&S. But.....the bottom line is...all the internals are fine. Valves are opening as they should (now) and I have even compression in both jugs. After cleaning both hold in at around 65-70lbs. Where one was higher prior to cleaning the valve seats and heads. After reassembly and at about 40 degrees with sae30 and a new air cleaner the engine fired strait away with no hesitation. Thanks to every one who took part in this little challenge of "What's wrong" Sean aka Zippo

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