I have looked all around on the Internet and can't find it when checking a predator 212 with a compression gauge with stock compression what should the reading be ?
Predator 212 stock compression
- Thread starter romerider153
- Start date
True the PDF file does not say other than 8.5 : 1 Compression Ratio.
http://manuals.harborfreight.com/manuals/69000-69999/69727.pdf
Next I saw on GardenWeb about the Predator 212 should like most small engines have 120 psi and seems a lemon someone got had 30 psi. See (Chiefe's Post) I hope the valves were set right as otherwise a new engine will have too much over lap. My Briggs engine had the seat an valve wear to the point of no clearance. I fixed that by grinding the bottom of the valve stem and used a feeler gauge. Newer engines have adjustments wheel or screw.
http://forums2.gardenweb.com/discussions/1631207/predator-engine
Further web search got Ask.com got "How do you convert compression ratio to PSI?"
And with the equation:
14.7psi atmospheric pressure * 8.5 ratio = 124.95 psi (sea level) (pressure at altitude would be less and below sea level like Death Valley more)
http://www.ask.com/science/convert-compression-ratio-psi-825aedc74e6b59d7
And still further I found about Valve Cross Over that means cam lifter spec info needed and it gets it more refined. Other small amount also noted here about the head and head gasket This on Hotrod.com and also Hotrodders.com:
http://www.hotrod.com/how-to/engine/ctrp-0505-calculating-engine-compression/
http://www.hotrodders.com/forum/compression-ratio-compared-compression-psi-55398.html
Just want to add that if you are not really doing racing for competition the one used for general trouble shooting like 30 psi as opposed to 120 psi roughly, that gets the job done.
Hey I learned something. But wearing of valve and seat just so you know had my Briggs 3 hp 80's era engine not only low compression, it also had another problem related to valve wear.
The intake stays open after BDC and the compression stroke starts. A little of this is normal called cross over. With my clearance between tappet and valve stem bottom at zilch this is how it went.
2/3 of the piston travel on compression stroke the intake valve is still open wasting valuable pressure. Easy Spin Start or not this is too much cross over.
Hey the engine still ran, but it also was spraying gas at the air filter for a moment while it still had the intake open too long a time. The venturi of the carburetor was still effective and sucked gas from the bowl as normal, just pressure, not vacuum, was the force and fuel spray opposite out the opposite way.
Too many paper air filters wetted. A fuel soaked air filter was cause to have me almost stranded as it chokes for air and never starts again until it dries out. If you have time before night fall well just wait.
Prior the engine had the original air filter and that type was of an oil bath air filter type which was not really affected by fuel spray the wrong way. It probably did the oil bath no good, and wasted a bit of fuel too.
I changed the carburetor to a gravity bowl feed system as it fit better on the frame, but oil bath air filter was no longer a choice.
MT
http://manuals.harborfreight.com/manuals/69000-69999/69727.pdf
Next I saw on GardenWeb about the Predator 212 should like most small engines have 120 psi and seems a lemon someone got had 30 psi. See (Chiefe's Post) I hope the valves were set right as otherwise a new engine will have too much over lap. My Briggs engine had the seat an valve wear to the point of no clearance. I fixed that by grinding the bottom of the valve stem and used a feeler gauge. Newer engines have adjustments wheel or screw.
http://forums2.gardenweb.com/discussions/1631207/predator-engine
Further web search got Ask.com got "How do you convert compression ratio to PSI?"
And with the equation:
14.7psi atmospheric pressure * 8.5 ratio = 124.95 psi (sea level) (pressure at altitude would be less and below sea level like Death Valley more)
http://www.ask.com/science/convert-compression-ratio-psi-825aedc74e6b59d7
And still further I found about Valve Cross Over that means cam lifter spec info needed and it gets it more refined. Other small amount also noted here about the head and head gasket This on Hotrod.com and also Hotrodders.com:
http://www.hotrod.com/how-to/engine/ctrp-0505-calculating-engine-compression/
http://www.hotrodders.com/forum/compression-ratio-compared-compression-psi-55398.html
Just want to add that if you are not really doing racing for competition the one used for general trouble shooting like 30 psi as opposed to 120 psi roughly, that gets the job done.
Hey I learned something. But wearing of valve and seat just so you know had my Briggs 3 hp 80's era engine not only low compression, it also had another problem related to valve wear.
The intake stays open after BDC and the compression stroke starts. A little of this is normal called cross over. With my clearance between tappet and valve stem bottom at zilch this is how it went.
2/3 of the piston travel on compression stroke the intake valve is still open wasting valuable pressure. Easy Spin Start or not this is too much cross over.
Hey the engine still ran, but it also was spraying gas at the air filter for a moment while it still had the intake open too long a time. The venturi of the carburetor was still effective and sucked gas from the bowl as normal, just pressure, not vacuum, was the force and fuel spray opposite out the opposite way.
Too many paper air filters wetted. A fuel soaked air filter was cause to have me almost stranded as it chokes for air and never starts again until it dries out. If you have time before night fall well just wait.
Prior the engine had the original air filter and that type was of an oil bath air filter type which was not really affected by fuel spray the wrong way. It probably did the oil bath no good, and wasted a bit of fuel too.
I changed the carburetor to a gravity bowl feed system as it fit better on the frame, but oil bath air filter was no longer a choice.
MT
I checked mine cold it was 75psi I then fired it up and it was 85psi. everything I build I usually try to have atleast 125. I did notice that this engine right from the start was incredibly easy to turn over just by hand on the flywheel. I also changed the oil for the first time today and noticed a slight metallic glistening from the oil I assume it is ok since it's still breaking in I'm sure and there is no form of oil filtration.
From that simple equation and others post saying around 120, yep!
Have you looked at the valve setting both intake and exhaust!
**************************************************
VOID REMARK INCORRECT.... HAS COMPRESSION RELEASE SEE POSTs 7 PG1
and also link to video FFV8 found on compression release post 15 16 & 17 on page 2
There is no automatic decompression release for easy starting on this engine so that could be eliminated as faulty.
**************************************************
MT
Have you looked at the valve setting both intake and exhaust!
**************************************************
VOID REMARK INCORRECT.... HAS COMPRESSION RELEASE SEE POSTs 7 PG1
and also link to video FFV8 found on compression release post 15 16 & 17 on page 2
There is no automatic decompression release for easy starting on this engine so that could be eliminated as faulty.
**************************************************
MT
Last edited:
Valve Clearance
Intake
0.10 - 0.15 mm
Exhaust
0.15 - 0.20 mm
http://manuals.harborfreight.com/manuals/69000-69999/69727.pdf
Intake
0.10 - 0.15 mm
Exhaust
0.15 - 0.20 mm
http://manuals.harborfreight.com/manuals/69000-69999/69727.pdf
Page 6 of manual. (Note this is user not service manual) The how to adjust valves I did not see there, but it is probably on the internet for that particular engine. It differs from my old Briggs as it has Over Head Cam. The valve cover removed and how to position the cranks shaft are the particulars needed. I could not say as I have not explicitly worked on those engines.
Others here will probably chime in and you can get help if that is all. Otherwise what about warranty if not too late?
My engine was one of 3 engines I got at San Jose flea market for 25 dollars years ago, they had to have the valve seats and valve angles re-cut. I found a shop they did each valve or seat for 10 dollars. Two of my three engines seal really good at the valves. Honing the cylinder I was told by the shop it did not need.
MT
COMPRESSION RELATED:
1.
Cylinder not lubricated. Problem after long
storage periods.
2.
Loose or broken spark plug. (Hissing
noise will occur when trying to start.)
3.
Loose cylinder head or damaged
head gasket. (Hissing noise will
occur when trying to start.)
4.
Engine valves or tappets
mis-adjusted or stuck
Others here will probably chime in and you can get help if that is all. Otherwise what about warranty if not too late?
My engine was one of 3 engines I got at San Jose flea market for 25 dollars years ago, they had to have the valve seats and valve angles re-cut. I found a shop they did each valve or seat for 10 dollars. Two of my three engines seal really good at the valves. Honing the cylinder I was told by the shop it did not need.
MT
COMPRESSION RELATED:
1.
Cylinder not lubricated. Problem after long
storage periods.
2.
Loose or broken spark plug. (Hissing
noise will occur when trying to start.)
3.
Loose cylinder head or damaged
head gasket. (Hissing noise will
occur when trying to start.)
4.
Engine valves or tappets
mis-adjusted or stuck
I had an engine where the cup retainer for a valve spring broke, yep no moving valve there was absolutely no compression. But you say your engine runs, so see the trouble shooting areas listed in the user manual online.
Even if it is out of warranty by a little bit I would see if they would help. Mostly I know they always want you to buy the contract extended warranty.
MT
Even if it is out of warranty by a little bit I would see if they would help. Mostly I know they always want you to buy the contract extended warranty.
MT
http://motorbicycling.com/showthread.php?t=60384
Your other thread I now correlate with that same Predator 212 engine.
The slant position (possibly 50 degree) that it's on, I hope the lubrication works OK with oil filled with that extra amount you figured.
Are you testing the compression with it off the bike from that slant position. It is really apples and apples only if you keep the engine within specs of the tilt allowed. Best to put on flat test platform and do the test.
My Briggs allows for 15 degrees of tilt fore or aft I think. It is what I have aft tilt, except when the bike goes up hill.
The crankcase I looked at and the splash fork would still be OK, but forward tilt 15 degree plus going down hill, it would not splash as well. It truly was not reason for aft tilt, just the frame at the time I was afraid of cutting and re-welding. I since have done a clearance issue where 1/4 the weight of the bike and I was modified by cut away and add weld metal. One side of the rear stay for sheave belt clearance was first of welds that so far have held, on very rough trail riding.
Check after the valves if OK what others that run engines tilted like that, see what they know.
Your other thread I now correlate with that same Predator 212 engine.
The slant position (possibly 50 degree) that it's on, I hope the lubrication works OK with oil filled with that extra amount you figured.
Are you testing the compression with it off the bike from that slant position. It is really apples and apples only if you keep the engine within specs of the tilt allowed. Best to put on flat test platform and do the test.
My Briggs allows for 15 degrees of tilt fore or aft I think. It is what I have aft tilt, except when the bike goes up hill.
The crankcase I looked at and the splash fork would still be OK, but forward tilt 15 degree plus going down hill, it would not splash as well. It truly was not reason for aft tilt, just the frame at the time I was afraid of cutting and re-welding. I since have done a clearance issue where 1/4 the weight of the bike and I was modified by cut away and add weld metal. One side of the rear stay for sheave belt clearance was first of welds that so far have held, on very rough trail riding.
Check after the valves if OK what others that run engines tilted like that, see what they know.
Attachments
Last edited:
Well the engine runs fine and I have oil in the valve cover so I'm sure that's not a issue I was just doing some runs and checking the plug iv been slowly drilling the jet bigger and it's made a big difference and I'm getting a nice plug reading. I just tested compression for kicks and was very surprised it was only 85.
http://motorbicycling.com/showthread.php?t=59109
(here I see some one questioning 85 psi?) Post 1 & post 2 see!
http://motorbicycling.com/forumdisplay.php?f=52
Heads & Cylinders section of forum
Go here as this is the location where your answer is more direct to the sections on the forum.
MT
(here I see some one questioning 85 psi?) Post 1 & post 2 see!
http://motorbicycling.com/forumdisplay.php?f=52
Heads & Cylinders section of forum
Go here as this is the location where your answer is more direct to the sections on the forum.
MT
Last edited:
This is the compression release on the 212:
https://www.youtube.com/watch?v=6uTYXaAtzNU
It operates with centrifugal force. When the engine is stopped, the small arm moves in to the path of the tappet. It bumps the Exhaust valve open briefly on the compression stroke.
If you spin the cam in a lathe, it seems to clear the tappet path about 350 rpm. That would be about 700 crankshaft rpm.
That is why you can't get a good compression test pulling the rope - and why the manufacturer never lists compression test pressures.
As for the oiling, you just need to maintain the oil level in the same relationship to the crankshaft centerline that the original orientation had.
When you rotate the engine, the rod still swings through the sane arc it always did. If the oil level is the same distance from the crank centerline, the dipper still dips just as much.
https://www.youtube.com/watch?v=6uTYXaAtzNU
It operates with centrifugal force. When the engine is stopped, the small arm moves in to the path of the tappet. It bumps the Exhaust valve open briefly on the compression stroke.
If you spin the cam in a lathe, it seems to clear the tappet path about 350 rpm. That would be about 700 crankshaft rpm.
That is why you can't get a good compression test pulling the rope - and why the manufacturer never lists compression test pressures.
As for the oiling, you just need to maintain the oil level in the same relationship to the crankshaft centerline that the original orientation had.
When you rotate the engine, the rod still swings through the sane arc it always did. If the oil level is the same distance from the crank centerline, the dipper still dips just as much.
I forgot all about the compression release. My bike is electric start but even still I don't think the starter gets it up to 700 rpm. I still am going to check lash just for ****s since I didn't do it before installing the motor. Thanks mt and ffv
Something about refreshing pages or some delay with seeing others posts..... did not see FFV8's earlier post til now.
I stand corrected auto compression release is on this engine. Post 5 forget that I said it does not have one. There is no mention of it in the text. But zooming in 800 % at the cam and you see a spring, must be part of this compression release.
Still if you run as was said at throttle wide open, what is there a way you can be testing compression. Ya know, you have to have a spark plug to run the engine, right?
What was it that was done, meaning at wide open throttle? That in post of other thread:
http://motorbicycling.com/showthread.php?t=59109
**** I think I understand after a thought, you warm up the engine that is all. At no time is compression tested while engine runs. The throttle (meaning probably the butterfly valve) must be wide open and you hand crank the engine with the recoil starter. The throttle if not open fully must affect the reading. The engine that this was mentioned on in the other thread probably does not have compression release so if the engine runs well, maybe the compression is OK after all. ****
I stand corrected auto compression release is on this engine. Post 5 forget that I said it does not have one. There is no mention of it in the text. But zooming in 800 % at the cam and you see a spring, must be part of this compression release.
Still if you run as was said at throttle wide open, what is there a way you can be testing compression. Ya know, you have to have a spark plug to run the engine, right?
What was it that was done, meaning at wide open throttle? That in post of other thread:
http://motorbicycling.com/showthread.php?t=59109
**** I think I understand after a thought, you warm up the engine that is all. At no time is compression tested while engine runs. The throttle (meaning probably the butterfly valve) must be wide open and you hand crank the engine with the recoil starter. The throttle if not open fully must affect the reading. The engine that this was mentioned on in the other thread probably does not have compression release so if the engine runs well, maybe the compression is OK after all. ****
Attachments
Last edited:
