Lo 206 comp psi

Popatopracing said:
What should a stock 206 f
Have for comp psi on a gage
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maybe somebody else does, but I don't. I don't think it's really important what the peak PSI is. What is important is if it drops. After you break the engine in, check the compression pressure. Go race. Before going home check it again. Do that after every race. If it goes down, that indicates a problem. At this point, if you do a leak down test, you can determine if it's the valves giving you the problem. If the valves are not leaking, it must be the rings.

Comments compliments criticisms and questions always welcome.
If the data does not support the theory, get a new theory.(Al Nunley)
 
I usually just do a leak down test it is hard to get a good comp psi reading because of the compression release on the cam shaft im sure there is a way to do it but im not sure how
 
I will do a leak down test tomarow it has 30 psi for comp motor ran mint last year now it. Has no power I had the pipe bracket welded could that have messed up the ignition
 
The compression release associated with the exhaust lobe (for starting) will lift the valve .030-.040. Might be the reason for a low number. That said, you have to account for it. Compression test, by itself, sheds little light on the ring & valve seal. Leak-down test is the preferred choice.
 
Gonzari said:
The compression release associated with the exhaust lobe (for starting) will lift the valve .030-.040. Might be the reason for a low number. That said, you have to account for it. Compression test, by itself, sheds little light on the ring & valve seal. Leak-down test is the preferred choice.
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And no one ever said the compression check would shed any light on whether it's the ring or valve seal, not individually at least. If you make a compression check, and it's down, (and a compression check is real quick and easy) then you know it's the rings or the valves leaking. Then you do a leak down test to discover which one is leaking. You have to admit that a compression check is much easier to do than a leak down test. When you're at the track, it's not important to know which is leaking, it's only important to know if the compression is down. After all, if the compression is down, you're not going to fix it at the track, are you?

The resistance I see to the compression check is unreasonable IMHO! It is so fast, and so easy, and tells you so much, it seems unreasonable to me that people will not adopt it.

From the desk of Al Nunley
Comments compliments criticisms and questions always welcome.
If the data does not support the theory, get a new theory.(Al Nunley)
 
A compression test can vary so much from engine to engine, then explains little. Most tuners, through a process of elimination, are all about isolating the problem, then fixing it. Popotopracing can do that compression test, but there's no point of reference to compare HIS number to. Pulling the head is so simple, then test for leakage.

He's my technique when a quick test is needed: Find a rubber stopper that plugs both the intake & exhaust ports. Drill a 1/16" hole through the center of the plug, then insert an 1/8" brass tube through it. Attach an 1/8" plastic line to it, and you have a portable tool. Insert the rubber stopper into the port, turn the head w/ the valve-seats skyward, add a bit of WD40 to the chamber (with the head completely assembled) then blow through the tubing. Repeat for both intake & exhaust ports.

You'll probably see leakage around the exhaust valve due to EGT's being far higher than the intake. It's a 15 minute check, usually confirms that valve seal was the culprit. BTW, we can & do fix that issue at the track, by putting another head on the motor....if rules allow.

https://www.youtube.com/watch?v=S3uw2z2l8-8
 
Al, are you understanding of the compression release mechanics on this engine? At cranking speed it releases a large part of the compression pressure to facilitate hand starting. It centrifugally moves away at engine start to give max compression that engine has to offer. It would have to spin at a relatively high rpm to get a usable compression check.
 
Flash-o-matic said:
It would have to spin at a relatively high rpm to get a usable compression check.
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two cycle racers use a starter motor. Why can't you? People obsess endlessly about gear ratios, and changing gear sets, and which clutch is better, and which chain is better, and which flywheel is better, and yet they care not to go to the trouble, and expense, to check the compression pressure. Compression is the Holy Grail. All things being equal, the engine with the highest compression, is going to put out the most horsepower, a fact that cannot be disputed.

I don't dispute that the leak down test serves a useful purpose. After all, if the compression is down you want to know if it's the rings or the valves.

And by the way, if I see somebody at the track changing heads, without the tech man there, I'm sure I would want to know why. In two cycle racing, after you qualify, they paint several things just to make sure that you don't do something like that.

From the desk of Al Nunley
Comments compliments criticisms and questions always welcome.
If the data does not support the theory, get a new theory.(Al Nunley)
 
Because the Lo206 is a spec class from Briggs and Stratton and it has a pull start and you can't change it. If people dont want a Lo206 with a pull starter they can go buy an animal.

Not everyone can run a 2 cycle Al. The most compression may make the most horsepower but how can we compare it? Use the same dyno on three different motors that all run an octane to match their compression and see which makes the most? Probably, but I believe that horsepower is irrelevant to torque and how you transfer that to the wheels in any form of racing.

Sorry to get off topic hope you find what is going on with your motor Popatop.
 
BrendanFitz #73 said:
Because the Lo206 is a spec class from Briggs and Stratton and it has a pull start and you can't change it. If people dont want a Lo206 with a pull starter they can go buy an animal.

Not everyone can run a 2 cycle Al. The most compression may make the most horsepower but how can we compare it? Use the same dyno on three different motors that all run an octane to match their compression and see which makes the most? Probably, but I believe that horsepower is irrelevant to torque and how you transfer that to the wheels in any form of racing.

Sorry to get off topic hope you find what is going on with your motor Popatop.
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did I ever say anything about taking the pull starter off?
Is there a rule against checking your compression with an electric starter? At home?
"Horsepower is irrelevant to torque"?? I don't know where you came up with that. Or what you're trying to tell me. Maybe I misunderstand. I've done it before.
Did you know that horsepower is a calculation? Torque x RPM / 5252.1 = horsepower. So they're hardly irrelevant to each other. Torque is work. "Horsepower" is a name given to the sum of the equation, torque x RPM / 5252.1.
Two cycle four cycle, makes no difference. How can you compare it? I don't understand that question. And who matches their octane to their compression? If I understand you right, no one knows what their compression is, and this tells me they have no idea what octane to use. Not precisely in any case. And most don't even know what octane is, or what it does. You would be surprised at the number of people that run high-octane premium, or even high-octane race gas, in their low compression engines.

From the desk of Al Nunley
Comments compliments criticisms and questions always welcome.
If the data does not support the theory, get a new theory.(Al Nunley)
 
For the purposes of the compression test you could pull the side cover off and spin it with a starter. Note RPM and ADR if you wanna get really detailed.
Leakdown is a good way to go. I measured 4% leakdown on mine, consistent at 20PSI, 50PSI and 100PSI
 
Side cover has seals on it. You can cut the seals if you like but then it's no longer a legal L0 206
 
Why can't you simply just spin it from the crank ?
According to Briggs website this motor has a nine to one compression ratio , which should be good for 85 to 88 octane gas .
The only way to do a compression test on this engine would be to weld the compression release closed on the cam so that it does not release the compression . I said it once and I'll say it again torque gets you moving horsepower get you going faster . More horsepower for life .
 
the easy explanation would like to have a clidesdale horse pulling your heavy wagon or a quarter horse. the clidesdale has a lot of pulling power but not much speed. (torque) the quarter horse has lots of speed but very little pulling power. (horsepower)
 
You don't have HP without torque, Torque is simply a rate at which the torque is applied. Doesn't matter how fast the horse is if it can't move the load.
 
I have to ask....and I know i'll catch crap for this....but why are you worried about it? Check the valve lash often and lap the valves over the winter and dont worry about it for a few years. One winter you will pull the head off and look and the bore and know its time to swap out the short block. Have 4 years on both of my motors and they still run strong.
 
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