5 hp briggs compression problems

tundrabeagle3

tundrabeagle3

Member
#1
#1
I have a 5hp briggs and stratton engine that i have in my mini chopper that has been giving me some problems. When i ride it in high rpms (4900-5200) the motor skips a spark. also it takes a while to reach high rpms with my 6 to 1 ratio and 16 inch tire. i tested the compression and the highest i got was 45 ish psi . what steps should i take in fixing my problem? I am trying to hit 50 to 60 mph would it be a better idea to just get a predator and gear it higher or any other ideas? :shrug: sorry if im asking to many questions but i have been fixing this motor for some time now and would like to have it running good or replace it so i can start to enjoy the mini chopper . thanks
 
Miniwood

Miniwood

New Member
#2
#2
You cant get a proper pressure reading on these engines. Briggs does not recomend pressure readings. 45 is about what i got after i put new rings in.
Sounds like tou have coil or spark issue. Have you changed the plug?
Coil only?
I love working on these briggs because they are so simple. But i really need a good block to build.
Saw the HF predator for 119 Yesterday. Not sure if you can find a coupon.
Not sure if you can hit your goal with a stock 5 hp briggs without some gearing and still be able to take off.
Are you are running a tq converter?
tundrabeagle3 said:
I have a 5hp briggs and stratton engine that i have in my mini chopper that has been giving me some problems. When i ride it in high rpms (4900-5200) the motor skips a spark. also it takes a while to reach high rpms with my 6 to 1 ratio and 16 inch tire. i tested the compression and the highest i got was 45 ish psi . what steps should i take in fixing my problem? I am trying to hit 50 to 60 mph would it be a better idea to just get a predator and gear it higher or any other ideas? :shrug: sorry if im asking to many questions but i have been fixing this motor for some time now and would like to have it running good or replace it so i can start to enjoy the mini chopper . thanks
Click to expand...
 
tundrabeagle3

tundrabeagle3

Member
#3
#3
i put a new plug in it and im running a clutch. i also read on here of people having around 90 to 100 psi with their 5 hp briggs. could it be a valve problem?
 
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Miniwood

Miniwood

New Member
#4
#4
Briggs have compression release built in. You can take off the shroud and push the flywheel backwards by hand and watch it kick back.
According to briggs
 
tundrabeagle3

tundrabeagle3

Member
#6
#6
just tried turning the flywheel back wards and it doesnt spin back. i dont think theres a compression release its an older 5 hp briggs flat head. any 5 hp briggs veterans have any ideas?
 
The Restore Kid

The Restore Kid

New Member
#7
#7
Your compression is real low.. Typically 90 PSI is a usual minimum on anything really.. Maybe less on an old hit an miss engine or Rumley Oil Pull that burns kerosene.. But 90 really is good enough to go ya typically..

The compression release is in the camshaft... :doah: The intake valve floats open for a good portion of the pistons travel.... The intake valve opens as the piston is going down.. Sucks in some air fuel, the intake valve drops shut as the piston is coming up..

BUT!!! instead of the valve snapping shut and sealing off... The valve hangs open just a couple thousandths of an inch for most of the pistons travel..... So it is basically a controlled valve leak.. THEN when the piston is like 3/4 7/8 to top dead, the valve finally drops into place and actually SEATS so it can create compression and and fire...

So... every so often throughout life.. you will need to remove the intake valve, grind a couple thousands of an inch off from the stem.. until the clearance is right, and is seating at the right time and it will run and start way better...

You need to set your valve lash
 
tundrabeagle3

tundrabeagle3

Member
#9
#9
i just took the valve cover and head off the engine. both valves seem to be sealing fine after some adjustment. my exhaust valve stays open up until 7/8 tdc . but my intake valve stays open until 1/2 tdc . so im gonna try replacing the intake spring it seems very worn . i also wanted to try increasing the timing to run 91 but cant find the timing key on the flywheel can some post a pic of it please?
 
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The Restore Kid

The Restore Kid

New Member
#10
#10
Derp.. :laugh: Ohhh this is an OHV engine? Eh... same principle applies, you just HAVE TO USE feeler gauges to get the clearance set right between your valve stem and lifter, as apposed to I can just eyeball it on a Flathead because I've done so many.. :laugh:
 
jeep2003

jeep2003

#11
#11
thats your problem your only getting 1/2" worth of compression. do like trk said and shave the back of your valve stems until you get somthing like 3/4 of the throw giving you compression. I do it on all of mine itll wake it right up :thumbsup:
 
tundrabeagle3

tundrabeagle3

Member
#13
#13
its a 5 hp flathead, is the point of shaving the valve stems to make the valves shut all the way? if so mine already shut all the way, the intake just closes too soon. im guessing its the intake valve spring because i took it out and can easily compress it with my fingers.
 
The Restore Kid

The Restore Kid

New Member
#14
#14
No the intake valve spring usually is pretty limp compared to the exhaust spring.. It saves on destruction but mostly just limits how fast the engine can get going...

It's not the fact that intake valve isn't closing all the the way... the intake valve isn't closing all the way FAST ENOUGH!! It's not closing too fast, it's closing too slow.. thats why it has low compression.... There's like 3 or four stages in the intake lobe on the cam... the intake valve is SUPPOSED TO SEAT TIGHT at like stage 3.25 - 3.5 in the lobe or whatever.... But yours is waiting till it's completely THROUGH into step 4 before it closes tight...

Because the valve lash needs to be re-set.. :thumbsup:
 
tundrabeagle3

tundrabeagle3

Member
#15
#15
that makes sense , ok im going to grind the bottom of the valve a tiny bit with the dremel , i also wanted to advance the timing a little to run higher octane . i figured it would be easier to just move the ignition a little, would i move it to the left or right to advance timing? thanks for help trk
 
The Restore Kid

The Restore Kid

New Member
#16
#16
Moving the flywheel clockwise will advance it... It's spinning clockwise, so any farther forward it is, the faster the spark gets there..

Look up setting your valve lash and make sure to do it right.. If ya over do it, it won't run for squat... You can over do it just a tad bit and make it run stronger, but it's rough on flywheel keys and starter parts and what not..
 
Miniwood

Miniwood

New Member
#17
#17
Take a piece of news paper and try to slide it between the valve spring and tappet after the valve is seated. If it doesnt slide thru the gap its too tight.

Newspaper.0025 folded in half .0050
Intake and exhaust gap just over .0050
 
F

Flexmod3

New Member
#19
#19
oldfatguy said:
the problem with grinding the valve is you are losing lift height. The best way is to remove the material from the cam
Click to expand...


Do you by chance have a picture of the lobe we should remove from? Asking because TRK stated it's got like 4 stages, and wanna make sure I shave the right part...
 
oldfatguy

oldfatguy

Active Member
#20
#20


this is how I do them, I set the cam up in the lathe and use a dial indicator to measure the exhaust lobe. Then I turn the lathe chuck back and forth by hand to cut the high spot off the cam lobe. The part the needs to be cut is the part of the exhaust lobe the contacts the lifter during the compression stroke. This can be done with a file and checking the valve lash .When done , the dial indicator will read the same all the way around the round part of the cam lobe
 
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