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Too much compression?

#1

F

familyman121712

I have a poulan pro riding mower with a briggs and Stratton 19hp ohv engine. The battery us fully charged, the starter is brand new, I've checked the valve lash and made sure they are moving. Compression still stops the crank. Any ideas?


#2

Scrubcadet10

Scrubcadet10

most likely its a engine with the known Automatic Compression release failure... you should see the intake valve bump open on the compression stroke if you remove the valve cover and rotate the engine by hand,
also post the engine Model and Type numbers, they are stamped into the valve cover.


#3

StarTech

StarTech

Second the ACR failure. Quite common. Camshafts are currently on back order. They had an ETA 07/15/2021 but that has passed and no camshafts yet.


#4

F

familyman121712

Scrubcadet10 said:
most likely its a engine with the known Automatic Compression release failure... you should see the intake valve bump open on the compression stroke if you remove the valve cover and rotate the engine by hand,
also post the engine Model and Type numbers, they are stamped into the valve cover.
Click to expand...


#5

F

familyman121712

Model # 33r877. Type # 0009 g1. Can you go a little more in depth on the acr? Ive never heard of it, but I'm not really a small engine guy.


#6

I

ILENGINE

StarTech said:
Second the ACR failure. Quite common. Camshafts are currently on back order. They had an ETA 07/15/2021 but that has passed and no camshafts yet.
Click to expand...
Currently showing 8/2/21 for me, but we will see.


#7

I

ILENGINE

familyman121712 said:
Model # 33r877. Type # 0009 g1. Can you go a little more in depth on the acr? Ive never heard of it, but I'm not really a small engine guy.
Click to expand...
It consist of a weight, and return spring and a rod that bumps the intake valve off slightly just before TDC to drop the compression down when cranking to assist the starter to turn the engine over. It then moves out of the way to allow full compression while running. The problem is the weight breaks off and will end up in the bottom of the engine sump and without it working the compression is too high for the starter to crank the engine past compression stroke.

Very known common problem and I have personally been waiting on a backordered camshaft since April for a customers mower.


#8

M

mechanic mark

Results

www.briggsandstratton.com www.briggsandstratton.com
Your valve clearance is on top left of page 10 in Operators Manual posted above. Intake valve .003-.005 / Exhaust valve .005- .007. I myself would set intake valve lash at .004 & exhaust valve lash at .006.
Don't give up yet, watch video above for proper valve adjustment procedure.


#9

F

familyman121712

ILENGINE said:
It consist of a weight, and return spring and a rod that bumps the intake valve off slightly just before TDC to drop the compression down when cranking to assist the starter to turn the engine over. It then moves out of the way to allow full compression while running. The problem is the weight breaks off and will end up in the bottom of the engine sump and without it working the compression is too high for the starter to crank the engine past compression stroke.

Very known common problem and I have personally been waiting on a backordered camshaft since April for a customers mower.
Click to expand...
Crap. That does sound exactly like what its doing.


#10

StarTech

StarTech

IL, I think I see why the ACRs are failing and it is a design problem. Even when the ACR is fully retracted the pin is still loose enough to be constantly bump by the tappet rocking the pin until it breaks off sending the ACR weight flying across the engine. It is just like you bending a piece until it breaks. And sometimes it takes out the governor while at it along other damage. The last two I did use aftermarket camshafts ACR had damage the governor too. THe next to last one actually snag the cylinder a little, lucky it was just a nick.


#11

M

mechanic mark

familyman121712 said:
Crap. That does sound exactly like what its doing.
Click to expand...
Don't assume anything or get down, read my post above & watch video.
Read above by clicking on website. Are you sure you were on correct stroke when adjusting valves? You may have been 180 degrees off. With spark plug out, engine cold of course, insert dowel, pencil, screwdriver, etc. making sure piston is at TDC, top of stroke, then go 1/4" past, both rocker arms should be loose & even with valves closed. You are now ready to adjust both intake & exhaust valves to specs.


#12

F

familyman121712

mechanic mark said:
Don't assume anything or get down, read my post above & watch video.
Click to expand...
Yep, did that last night. Matter of fact thats the same video I found.


#13

F

familyman121712

familyman121712 said:
Yep, did that last night. Matter of fact thats the same video I found.
Click to expand...
Sorry, hit the button before I finished. When I checked the lash before I reset it, they were at .005 intake and .008 exhaust. I set them to .004 and .006 like you suggested.seemed like a good spot right in the middle of tolerance. Didnt change anything, though.


#14

Scrubcadet10

Scrubcadet10

Parts tree shows the cam as in stock (leaves within 1 business day)
www.partstree.com

PartsTree - Home of OEM Parts for Outdoor Power Equipment

Parts lookup and repair parts diagrams for outdoor equipment like Toro mowers, Cub Cadet tractors, Husqvarna chainsaws, Echo trimmers, Briggs engines, etc.
www.partstree.com www.partstree.com
Appears available at jacks.
also plenty of Chinese aftermarkets on amazon. https://www.amazon.com/s?k=84005207&i=automotive&ref=nb_sb_noss_1
although star tech has mentioned issues with the cam journals being slightly over sized.


#15

StarTech

StarTech

Either way telcon either vendor to be sure they have it in stock. Jacks is bad at having to order items after you order it.


#16

I

ILENGINE

StarTech said:
IL, I think I see why the ACRs are failing and it is a design problem. Even when the ACR is fully retracted the pin is still loose enough to be constantly bump by the tappet rocking the pin until it breaks off sending the ACR weight flying across the engine. It is just like you bending a piece until it breaks. And sometimes it takes out the governor while at it along other damage. The last two I did use aftermarket camshafts ACR had damage the governor too. THe next to last one actually snag the cylinder a little, lucky it was just a nick.
Click to expand...
It is a sloppy design and I would agree that is the reason they are a high failure item.


#17

N

njswede

familyman121712 said:
I have a poulan pro riding mower with a briggs and Stratton 19hp ohv engine. The battery us fully charged, the starter is brand new, I've checked the valve lash and made sure they are moving. Compression still stops the crank. Any ideas?
Click to expand...
I was driving myself nuts trying to track down this issue. Tried new battery, valve clearance, starter solenoid and everything else. It ended up being a leaky needle valve seat in the carb. It caused the engine to aqua lock when it sat for a while. Take the plugs out. If gas comes pouring out then you have this problem. You then have two options: Rebuild/replace the carb or install a fuel valve you keep closed when you’re not using the mower.


#18

N

njswede

…also, if that turns out to be the problem, I highly recommend an oil change! More likely than not, you trying to crank it has pushed some gas past the piston rings and into the oil.


#19

S

SamB

I had this cam/ACR issue a while back. A "hack" I learned was if you just have to get the Briggs running to mow,covering the intake at the carb will not allow air into the engine and the engine will turn over fast enough to start as soon as you remove your carb covering. I used a piece of rubber I cut from an old floor mat. Hey,I did say it was a hack,but it does work. LOL!


#20

R

Ronni

familyman121712 said:
I have a poulan pro riding mower with a briggs and Stratton 19hp ohv engine. The battery us fully charged, the starter is brand new, I've checked the valve lash and made sure they are moving. Compression still stops the crank. Any ideas?
Click to expand...
I had the same problem with a new mower I had just bought. It turned out that gasoline was flooding through the carburetor and filled the piston with gasoline during the compression stroke. This totally locked up the engine from starting. It would not crank at all. I took it back to Lowes and got another mower in exchange.


#21

T

Tommy Mckeown

familyman121712 said:
Crap. That does sound exactly like what its doing.
Click to expand...
Some people have just used 2 head gaskets on the head with a little more torque down. This while lowering the overall compression seems to allow the starter to spin the motor to start.


#22

StarTech

StarTech

SamB said:
I had this cam/ACR issue a while back. A "hack" I learned was if you just have to get the Briggs running to mow,covering the intake at the carb will not allow air into the engine and the engine will turn over fast enough to start as soon as you remove your carb covering. I used a piece of rubber I cut from an old floor mat. Hey,I did say it was a hack,but it does work. LOL!
Click to expand...
But does anyone want a piece or several bouncing around in the engine doing all kinds of damage?


#23

S

SamB

StarTech said:
But does anyone want a piece or several bouncing around in the engine doing all kinds of damage?
Click to expand...
You are so right. Answer is..absolutely not! I took the bottom end off and removed the pieces while waiting for a replacement cam. I thought it best to not go with a used or an aftermarket cam,so there was some wait time. The grass didn't wait.. Not a difficult job.


#24

J

jamesds016

familyman121712 said:
I have a poulan pro riding mower with a briggs and Stratton 19hp ohv engine. The battery us fully charged, the starter is brand new, I've checked the valve lash and made sure they are moving. Compression still stops the crank. Any ideas?
Click to expand...
The acr is on the exhaust side of the cam. And they do have common failure rather frequently.


#25

I

ILENGINE

jamesds016 said:
The acr is on the exhaust side of the cam. And they do have common failure rather frequently.
Click to expand...
Incorrect. The briggs single cylinder OHV Intek style engine has a cross flow head and the intake is on the bottom of the head which is were the ACR is located.


#26

F

FLRMAN

Could it be a flywheel key sheared a little? I just repaired a push mower engine that was almost impossible to pull start. When it did turn over it fired and yanked the pull cord back. About broke my arm and it was only a 6.5 hp. I can't imagine a starter on a bigger engine being able to turn it over. Just a thought.


#27

S

slomo

What happened to the OP? Comes here asking for help then leaves. No hugs either LOL.

slomo


#28

Scrubcadet10

Scrubcadet10

slomo said:
What happened to the OP? Comes here asking for help then leaves. No hugs either LOL.

slomo
Click to expand...
I tried to give him a kiss but he..... oh that may have done it.........


#29

J

jamesds016

ILENGINE said:
Incorrect. The briggs single cylinder OHV Intek style engine has a cross flow head and the intake is on the bottom of the head which is were the ACR is located.
Click to expand...
Sir you are wrong I’ve been to many schools and replaced many of these so unless you have a picture to prove your correct then you are not.


#30

J

jamesds016

ILENGINE said:
Incorrect. The briggs single cylinder OHV Intek style engine has a cross flow head and the intake is on the bottom of the head which is were the ACR is
Click to expand...

ILENGINE said:
I do stand corrected. There is only 1 Briggs engine where the release is on the intake and it is a 19hp single cylinder engine that does have a common issue with the compression release failing.
Click to expand...


#31

StarTech

StarTech

jamesds016 said:
Sir you are wrong I’ve been to many schools and replaced many of these so unless you have a picture to prove your correct then you are not.
Click to expand...
Look IL is right about the 310000 series being a cross flow head of sorts. The intake port and exhaust ports are about the same height; therefore, intake port must cross over downwards (about 30 degrees) to the intake valve. Now the exhaust valve does have a straight shot at the exhaust port. Either way the paths are not a prefect criss cross but is very close. A true criss cross flow it is not. The old L heads the intake valve is always on top (magneto side) and the exhaust valve is on the bottom (PTO end).

As far going to schools I haven't been to a single small engine school in my life.

One advantage of this head design is the less fuel waste as all ACR vented fuel mixture is to the intake, One drawback is there is no way to fully clamp the head gasket in the area where the intake is crossing over leading to lots blown gaskets.

Now IL is wrong about the only Briggs 19 hp engines with the ACR on the intake as not only the 310000 but the 210000, 280000, and 330000 series also uses the same camshaft and head design. So far the most common ACR failures on these camshafts I have seen is only on the 310000 and 330000 but the camshaft is the same one in all four series. I just replace two 21hp 793880 camshafts this month alone.


#32

Scrubcadet10

Scrubcadet10

Dunno, just watched a video by EReplacement parts.com and they said the bottom valve is the intake... Which if it's on the bottom, it gets bumped.
Unless I've been adjusting valves on intek engines wrong for years.


#33

B

bertsmobile1

I can't remember the last OHV engine I worked on with the ACR on the exhaust
I will hazard a guess that ones again it would be an EPA regulation to prevent unburned fuel being emitted from the engine thus compression release shifted to the intake.


#34

StarTech

StarTech

Kawasaki v-twins have the ACR on the exhaust valves.


#35

I

ILENGINE

StarTech said:
Look IL is right about the 310000 series being a cross flow head of sorts. The intake port and exhaust ports are about the same height; therefore, intake port must cross over downwards (about 30 degrees) to the intake valve. Now the exhaust valve does have a straight shot at the exhaust port. Either way the paths are not a prefect criss cross but is very close. A true criss cross flow it is not. The old L heads the intake valve is always on top (magneto side) and the exhaust valve is on the bottom (PTO end).

As far going to schools I haven't been to a single small engine school in my life.

One advantage of this head design is the less fuel waste as all ACR vented fuel mixture is to the intake, One drawback is there is no way to fully clamp the head gasket in the area where the intake is crossing over leading to lots blown gaskets.

Now IL is wrong about the only Briggs 19 hp engines with the ACR on the intake as not only the 310000 but the 210000, 280000, and 330000 series also uses the same camshaft and head design. So far the most common ACR failures on these camshafts I have seen is only on the 310000 and 330000 but the camshaft is the same one in all four series. I just replace two 21hp 793880 camshafts this month alone.
Click to expand...
I didn't say that the 19hp was the only series with the cross flow head which is what Briggs call it. that was jamesds016 that said that. I knew all the single cylinder ohv engines which I should of clarified at the vertical engines, and not the small horizontal version of those engine. I knew that the 28-31-33 all used the same camshaft and have had ACR failures on all three. Haven't looked into the 210000 series so not sure about that one. Just haven't have camshaft failures on that series for my own experience.


#36

H

hlw49

Some times the cam lobes or gear can slip and cause it to kick back and not start. If it is the compression release most of the time you can turn the engine backwards by hand until you come up on compression. This way you have one full turn with no compression and the engine will start. But if the cam lobes or gear have slipped and it kicks back you will know it, really kicks back hard.


#37

H

hlw49

Haven't followed this threat and this may already been addressed but valve lash can cause kick back as well.


#38

G

GroundFisher66

StarTech said:
IL, I think I see why the ACRs are failing and it is a design problem. Even when the ACR is fully retracted the pin is still loose enough to be constantly bump by the tappet rocking the pin until it breaks off sending the ACR weight flying across the engine. It is just like you bending a piece until it breaks. And sometimes it takes out the governor while at it along other damage. The last two I did use aftermarket camshafts ACR had damage the governor too. THe next to last one actually snag the cylinder a little, lucky it was just a nick.
Click to expand...
Great info! I am having exactly the same problem. In addition, the ACR weight probably messed up my governor, because the engine runs at a substantially higher rpm now and has a higher rpm when idling. Thanks for the information.


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