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19.5 hp briggs opposed twin... very strange things are happening with it
#1
the_scrapsman
the_scrapsman
i got a 19.5 opposed twin thats on a 01 craftsman lt1000 and when i got it the guy said it ran off of starting fluid. i couldnt get it to run off of anything flammable so i chnaged out the coil to a new one and then i replaced carb thinking that was the issue but.... it wasnt. so i took the carb cack off, i took it apart, i combined the top and bottom of the two with eachother i tried every damn thing i could think of! it eventually ran on carb cleaner and ran good, no smoke and then i noticed fuel was being spit back up outta the carb... so i put my hand a couple inches above it sure a hell theres a nice strong push of air coming up out of the intake. my dad suggested covering the carb with a hand so we did and it stayed running and would not run without choke. now its running without choke but there was gas in the oil andit smoked some, blue smoke. it didnt use any, maybe the teeniest little bit but i changed the oil with some frsh stuff and i took it for a ride and it drank up most of it... that or i didnt put enough in which i swear i did. and it started to gain what i like to call "the well known oppy clatter" which it had this whole time but it gradually got worse and yeah. so the air is still coming up out of the intake you can hear it very clearly. any ideas on whats going on with this thing i confused briggs and stratton support and even a boatloads of other people... oh yeah and it quit smoking after the oil change it only does it on choke now. it runs okay theres a decent stutter to it even my junkyard briggs with pitted bores didnt have asmany problems as this ones having... it was out i the open with no air filter cover and no hood. so my questions are: why is the "known oppy clatter" getting worse? why is there air coming up out of the intake?
thanks for any help, the_scrapsman.
thanks for any help, the_scrapsman.
#2
H
hlw49
H
hlw49
Valves out of adjustment. A lot of those old apposed twins would rattle knock. That could be due to carbon build up on top of piston. Some of them just knock and run forever maybe top main bearing.
#3
the_scrapsman
the_scrapsman
its got really good compression thougfhValves out of adjustment. A lot of those old apposed twins would rattle knock. That could be due to carbon build up on top of piston. Some of them just knock and run forever maybe top main bearing.
#4
B
bertsmobile1
B
bertsmobile1
If the oil is thin & smells of fuel then the float valve is not cutting off the fuel supply .
#5
the_scrapsman
the_scrapsman
it is, i checked it i think it might valves and or ringsIf the oil is thin & smells of fuel then the float valve is not cutting off the fuel supply .
#6
H
hlw49
H
hlw49
Rings won't blow back out the carb. Will blow by the rings into the crank case. If you have access to a cylinder leak down tester it would tell you if it is leaking by the valve or the rings.it is, i checked it i think it might valves and or rings
What is really good compression? Oh and those old opposed twins had a problem with valve sets coming out. Check Compression Briggs & Stratton does not publish any compression pressures, as it is extremely difficult to obtain an accurate reading without special equipment. It has been determined through testing, a simple and accurate indication of compression can be made as follows: Remove both spark plugs and insert a compression gauge into either cylinder (one cylinder at a time). Open throttle wide open and choke open. Turn engine over with engine starter until there is no further increase in pressure. Record this reading. Repeat procedure on other cylinder and record that reading. The difference between both cylinders should not exceed 25%. More than 25% indicates loss of compression in the cylinder with lower pressure. See example. Example: Cyl. #1 Cyl. #2 Diff. % Diff. Eng. #1 65 PSI 60 PSI 5 PSI 7.6% Eng. #2 75 PSI 55 PSI 20 PSI 26.7% If compression is poor, look for – 1. Loose cylinder head bolts 2. Blown head gasket 3. Burned valves, valve seats and/or loose valve seats 4. Insufficient tappet clearance 5. Warped cylinder head 6. Warped valve stems 7. Worn bore and/or rings 8. Broken connecting rods Cylinder Leakdown Test The cylinder leakdown tester, Tool # 19413, may be used to test the sealing capability of the compression components of each cylinder and quickly identify the problem component.its got really good compression though
#7
B
bertsmobile1
B
bertsmobile1
You have 2 problems which are not really connected.
Excessive blow back through the carb is causes by a bad valve or blocked exhaust
Inlet is not closing fully so the compressing charge is being blown back out the carb as the piston rises
Blocked exhaust / exhaust valve not opening the cylinder may fire but the exhaust can not get out so it stays in the cylinder till the inlet opens and then blows back out the carb
Bring a side valve it is a PIA to get to the valve chest & observe so probably easier to pull both heads & watch the valves moving.
When I suspect bad valve timing but can not be sure I move the magneto (s) back off the flywheel then put some masking tape around the flywheel.
Then I do 2 full revolutions of the crankcase marking when each valve starts to open, is open fully and closes plus the piston when it is at TDC & BDC
Then I carefully remove the tape . lay it on the edge of some graph paper and plot the valves as a bar graph then plot the piston as a zig-zag line over the top.
While B & S do not publish their valve timing ( where I can access them anyway ) you will easily see if the cam is mistimed, one valve is not moving as it should
If you have a cheap vernier gauge with a depth gauge function then use it to measure the maximum valve lift , they should all be the same, within the limits of valve lash which on your engine is +/- o.oo5"
second problem is that carb
It is flooding .
To say they are a bitch to work on is a massive understatement .
I could write 40 pages on how to work on them buy their are a lot of You-tube videos that can show you how it is done , but it ain't easy .
Excessive blow back through the carb is causes by a bad valve or blocked exhaust
Inlet is not closing fully so the compressing charge is being blown back out the carb as the piston rises
Blocked exhaust / exhaust valve not opening the cylinder may fire but the exhaust can not get out so it stays in the cylinder till the inlet opens and then blows back out the carb
Bring a side valve it is a PIA to get to the valve chest & observe so probably easier to pull both heads & watch the valves moving.
When I suspect bad valve timing but can not be sure I move the magneto (s) back off the flywheel then put some masking tape around the flywheel.
Then I do 2 full revolutions of the crankcase marking when each valve starts to open, is open fully and closes plus the piston when it is at TDC & BDC
Then I carefully remove the tape . lay it on the edge of some graph paper and plot the valves as a bar graph then plot the piston as a zig-zag line over the top.
While B & S do not publish their valve timing ( where I can access them anyway ) you will easily see if the cam is mistimed, one valve is not moving as it should
If you have a cheap vernier gauge with a depth gauge function then use it to measure the maximum valve lift , they should all be the same, within the limits of valve lash which on your engine is +/- o.oo5"
second problem is that carb
It is flooding .
To say they are a bitch to work on is a massive understatement .
I could write 40 pages on how to work on them buy their are a lot of You-tube videos that can show you how it is done , but it ain't easy .
#9
Fish
Fish
Pull the heads and decarbon everything, and take a good look at everything.
#10
the_scrapsman
the_scrapsman
Ok thanksRings won't blow back out the carb. Will blow by the rings into the crank case. If you have access to a cylinder leak down tester it would tell you if it is leaking by the valve or the rings.
What is really good compression? Oh and those old opposed twins had a problem with valve sets coming out. Check Compression Briggs & Stratton does not publish any compression pressures, as it is extremely difficult to obtain an accurate reading without special equipment. It has been determined through testing, a simple and accurate indication of compression can be made as follows: Remove both spark plugs and insert a compression gauge into either cylinder (one cylinder at a time). Open throttle wide open and choke open. Turn engine over with engine starter until there is no further increase in pressure. Record this reading. Repeat procedure on other cylinder and record that reading. The difference between both cylinders should not exceed 25%. More than 25% indicates loss of compression in the cylinder with lower pressure. See example. Example: Cyl. #1 Cyl. #2 Diff. % Diff. Eng. #1 65 PSI 60 PSI 5 PSI 7.6% Eng. #2 75 PSI 55 PSI 20 PSI 26.7% If compression is poor, look for – 1. Loose cylinder head bolts 2. Blown head gasket 3. Burned valves, valve seats and/or loose valve seats 4. Insufficient tappet clearance 5. Warped cylinder head 6. Warped valve stems 7. Worn bore and/or rings 8. Broken connecting rods Cylinder Leakdown Test The cylinder leakdown tester, Tool # 19413, may be used to test the sealing capability of the compression components of each cylinder and quickly identify the problem component.
#11
the_scrapsman
the_scrapsman
Oh okYou have 2 problems which are not really connected.
Excessive blow back through the carb is causes by a bad valve or blocked exhaust
Inlet is not closing fully so the compressing charge is being blown back out the carb as the piston rises
Blocked exhaust / exhaust valve not opening the cylinder may fire but the exhaust can not get out so it stays in the cylinder till the inlet opens and then blows back out the carb
Bring a side valve it is a PIA to get to the valve chest & observe so probably easier to pull both heads & watch the valves moving.
When I suspect bad valve timing but can not be sure I move the magneto (s) back off the flywheel then put some masking tape around the flywheel.
Then I do 2 full revolutions of the crankcase marking when each valve starts to open, is open fully and closes plus the piston when it is at TDC & BDC
Then I carefully remove the tape . lay it on the edge of some graph paper and plot the valves as a bar graph then plot the piston as a zig-zag line over the top.
While B & S do not publish their valve timing ( where I can access them anyway ) you will easily see if the cam is mistimed, one valve is not moving as it should
If you have a cheap vernier gauge with a depth gauge function then use it to measure the maximum valve lift , they should all be the same, within the limits of valve lash which on your engine is +/- o.oo5"
second problem is that carb
It is flooding .
To say they are a bitch to work on is a massive understatement .
I could write 40 pages on how to work on them buy their are a lot of You-tube videos that can show you how it is done , but it ain't easy