Sign in to follow this  
Followers 0

Compression numbers ?

26 posts in this topic

Posted

Guys,

 

I'm getting a condition inspection on a 582 greyhead with about 150 hrs.  guy wants a compression check.  I cant seem to find any numbers .  What's good ? 70-80 -120 ?  engine warm or cold ?  is it really necessary to do one at all ?

 

thanks

 

EG     

Share this post


Link to post
Share on other sites

Posted

From an older article my Mike Stratman: "Good compression should read between 100-120 psi in both cylinders and 

equal at a minimum of 300 rpm"
 
Find the original article here" http://www.cps-parts.com/cps/pdf/Part47.pdf

Share this post


Link to post
Share on other sites

Posted

If your A&P is used to doing a compression check on the Continental and Lycosauris engines, you may have to convince him to use the automotive type compression gauge and starter, and not the blow-by type.

EDMO

Share this post


Link to post
Share on other sites

Posted

I bought my compression gauge at Autozone and test it warm through the hole that is straight now the angled one.

Share this post


Link to post
Share on other sites

Posted

 My trusty new Harbor Freight compression tester is giving me 80 psi on both cyl.  Seems odd that if it had a stuck ring etc. both cyls would give the exact same reading.  The engine is running smooth and turning a 70in Warp two blade (11 degree pitch) at 6500 static.  I ground ran it at 6500 for two minutes and the EGT ran 1050 and the water temp stabilized about 180.  You guys think this thing has problems ?

 

I sure appreciate your help.  No one around here know dick about a 582.  They are all busy trying to get the plastic covering off the interior cushions of their RV12s.  That thing must be the Crysler New Yorker of the homebuilt world !!     

Share this post


Link to post
Share on other sites

Posted

I feel your pain. On my field the only other two strokes are on the weed trimmers. Even the powered parachute guy is running a 912. At least the other guys are a little jealous that I get to do my own wrenching.

Share this post


Link to post
Share on other sites

Posted

The article says that anything BELOW 80 or 10% difference is cause for concern. Not sure what the 100-80 range means. Could just be your engine is ready for some rings. If they are both the same and it's running good.......I'll let you make the call. I went through the whole compression thing when I had my conditonal done the first time by a certified guy. After about 20 minutes of fiddling around in his toolbox trying to find an adapter for his tester and me biting my lower lip he finally just said we'll just do an engine run when were done. The fact that the engine ran satisfied him and he signed it off.

Share this post


Link to post
Share on other sites

Posted

O.K., so what to do if you have the pull-starter?  Hard to get a consistent compression value if you can't crank at a consistent rpm.  Facing my first conditional with a guy who doesn't have experience with 2-strokes.  Hopefully demonstrating 6200 rpm static full throttle will do, along with appropriate temps.

Share this post


Link to post
Share on other sites

Posted

O.K., so what to do if you have the pull-starter?  Hard to get a consistent compression value if you can't crank at a consistent rpm.  Facing my first conditional with a guy who doesn't have experience with 2-strokes.  Hopefully demonstrating 6200 rpm static full throttle will do, along with appropriate temps.

Just pull the cord, The compression tester will hold the reading and add the next pull to it. You got nothing to worry about there Turbo.

Share this post


Link to post
Share on other sites

Posted

 My trusty new Harbor Freight compression tester is giving me 80 psi on both cyl.  Seems odd that if it had a stuck ring etc. both cyls would give the exact same reading.  The engine is running smooth and turning a 70in Warp two blade (11 degree pitch) at 6500 static.  I ground ran it at 6500 for two minutes and the EGT ran 1050 and the water temp stabilized about 180.  You guys think this thing has problems ?

 

I sure appreciate your help.  No one around here know dick about a 582.  They are all busy trying to get the plastic covering off the interior cushions of their RV12s.  That thing must be the Crysler New Yorker of the homebuilt world !!     

I would either try another compression tester to try the compression tester on another engine.  My 582 has compression of 150psi (ish in both Cycl).

Share this post


Link to post
Share on other sites

Posted (edited)

Not really the question you were asking about, but if you are running at static 6500 rpm, you will most likely over rev the engine on climb out.  EGTs will most likely run much hotter, and then you are asking to experience that big silence when the fan stops turning.  6250 static would be a much better place.   JImChuk

PS  more related to your question, I checked the compression on a Hirth yesterday and it was 135 lbs in both cylinders. 

Edited by 1avidflyer

Share this post


Link to post
Share on other sites

Posted

Not really the question you were asking about, but if you are running at static 6500 rpm, you will most likely over rev the engine on climb out.  EGTs will most likely run much hotter, and then you are asking to experience that big silence when the fan stops turning.  6250 static would be a much better place.   JImChuk

PS  more related to your question, I checked the compression on a Hirth yesterday and it was 135 lbs in both cylinders. 

125 to 151 is normal. Most 2 strokes that are lower than 100psi are a real bugger to get started.

Share this post


Link to post
Share on other sites

Posted

Just to report to the group, my 582 Blue Head had 119 psi on each cylinder with 160 hours, and the next year had exactly the same reading (119 psi) with about 80 hours more time. These numbers were recorded with an electric starter.

Share this post


Link to post
Share on other sites

Posted

Mine tested at 115psi and 118 psi.  Only one problem.  My bowl floats are sinking!  Holy Moly are they pricy little buggers!  Is there another way out here?  Are the Bing 54 carbs used on snowmachines or something without wings?

Share this post


Link to post
Share on other sites

Posted

You might be able to get the floats through a BMW motorcycle parts supplier.   JImChuk

Share this post


Link to post
Share on other sites

Posted

Comparing both carbs, all the floats seem to be low riders!  Dried and shook them, and none had fuel sloshing inside.  One float bowl had the requisite half-inch level from the rim, the other less.  I am thinking that I just need to "rebuild" the bad carb, and of course clean them both.  Seems like the float-bowl level cutoff valve is the culprit for the bad carb.  Could just have a tiny piece of debris on the seat.  Sorry to have misappropriated the thread!

Share this post


Link to post
Share on other sites

Posted

I believe the floats are supposed to weigh at or less then a certain amount as a way of checking them.  3.5 grams seems like the right number.  Maybe this will jog someone else's memory and they can answer for sure.  Just googled it and I'm right.  JImChuk

https://www.rotax-owner.com/en/rotax-blog/item/34-912-914-float-inspection

Share this post


Link to post
Share on other sites

Posted

Compression Testers.

I've got to wonder if mine is accurate.  My 582 grey starts easily, and makes acceptable rpm behind an IVO IFA 70" prop. Yet, I'm only reading 90 psi on my non-descript gauge of 20 plus yrs old.  90 seems to low for an engine that runs so well.

Share this post


Link to post
Share on other sites

Posted

Egp8111, I'm a bit the newb here, but isn't 6500 static a bit high?  From what I understand, 6200 to 6300 is the rpm range to shoot for statically, so when you're moving thru the air, and the prop is unloaded somewhat, you aren't in danger of exceeding redline.  Now, I may be idiologically mistaken, comrade, but I see the compression test as only a crude indicator, since the engine in operation is turning way faster than even an electric starter can crank it, so any leakage past the rings will be fractionally way less.  I have read that worn-out 2-stroke engines become hard to start.  I'm sure there are folks on this site that have way more 2-stroke experience than I do.  What other symptoms say a 2-stroke engine is ready to suddenly stop running due to wear?  That IS the main concern, right?

Share this post


Link to post
Share on other sites

Posted

Probably way more likely to seize a 2 stroke engine and stop it then wear it out.   Cold seizures, to high of EGTs,  rings getting stuck with to much carbon build up which allows exhaust gasses to go down the side of the piston causing a hot spot.  Improper cooling will also cause problems.  JImChuk

Share this post


Link to post
Share on other sites

Posted

I dought that you will ever wear out a engine by the time you hit the recommended 300 hr overhaul time.

Share this post


Link to post
Share on other sites

Posted

A number of years ago, there was a guy from Oregon or Washington who had a 503 on his plane.  He flew it a lot, and he said he had 1250 hrs on that engine and it had never been apart.  He was going to fly the plane from his place to Oshkosh.  He post was about, should he trust the engine.   Lots of guys said that was to many hours, and they wouldn't do it.  At any rate, he started east, and the engine quit on him close to Yellowstone park (or maybe over it) At any rate, he was able to land on a small road with no damage.  He caught the bus to Oshkosh where he bought a new 503 and brought it back with him.  Installed it in the plane and flew back home.  Maybe some here remember that story.  He flew a lot with a little gal from Oregon who flew a Drifter from Oregon to Sun and Fun in Florida a few years back.  I think he flew the SnF trip also.  I guess the point of this whole post is these engines maybe can go a bit longer than Rotax's 300 hrs before they are worn out.  No doubt, four times longer is stretching it a bit though.  JImChuk

1 person likes this

Share this post


Link to post
Share on other sites

Posted

Oh, and on the compression check:  I only got 90 or so on the first pull.  Apparently it's o.k. to do multiple pulls to get that compression number.  After 4 or so pulls I got my final numbers, almost 120 psi.  Maybe that accounts for some of the diffs we see between good-running engines.

Share this post


Link to post
Share on other sites

Posted

When i work for a snowmachine repair shop when younger i was shown to pull the rope 3times like ur starting it on each cyl to get ur compression reading.  Id say 4 would b ok also long as u check both the same way and dont over do the pulling.  Hope thats right its always worked for me. 

Share this post


Link to post
Share on other sites

Posted

Also set the throttle to WOT to get a more accurate reading.

1 person likes this

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now
Sign in to follow this  
Followers 0