Even Compressions

[BigPete]

OK - this may sound a little paranoid BUT - ;)

 

How many Jabiru owners out their actually get 4/6 even weight compressions when they pull their motor thru for first start of the day? ;)

 

I have NEVER had 4 good strong compressions - always 1 or 2 a bit less (sometimes a lot????). I've been told this is quite normal?? :;)4:

 

My J160c now has 270 hrs and running fine.

 

(It's driving me crazy) :confused:

 

regards

 

 

[Geoff]

Maybe you were already :confused: Pete ;)

 

 

[Guest brentc]

I noticed that yet again yesterday on the pull through. Probably only about 2 of 6 on mine felt strong. Probably doesn't mean much as if it's not hot the rings won't be doing their job anyway.

 

 

[Alan]

230c (140hrs) - I am the same; it varies as to how many good compressions out of 6 I get during a cold pull through. I just put this down to the varied piston stop position with some valves open some closed etc leading to a variation in retained oil/fuel vapour. When hot the pull through evens (subjective decision) out.

 

Alan

 

 

[blueline]

Compressions when cold seem to be all over the place even on new engines (the J160 now has 500 hours and seems to have one always low when cold, J230 has 75 hours and it too has some low compressions when cold).

 

Does seem to get better when hot (as it should). Lycoming engines the same.

 

Leak down compression test on a hot engine is the only one that counts (but I can't help but notice when one is down on compression, even when cold).

 

I'm more worried about oil temps, especially as summer kicks in!

 

 

[Ross]

My J160 is yet to start but a cold pull through is generally "all over the place".

 

So what I do is every few days or so spin the motor up on the starter motor with both ignitions off, no fuel in the system anywhere, no plug leads and keep it up until oil pressure stabilises for a few seconds.

 

Pull throughs after that are generally good (to my unexperienced ear).

 

Regards

 

 

[Guest ozzie]

just wondering if the jab and 912 cylinders are of the "choked" type?

 

Ozzie

 

 

[Whack777]

Cold pull through for me on LSA 2.2 is irregular... as long as I feel some compression and don't hear any hissing at all, I am happy.

 

 

[Yenn]

My 2.2 Jab with about 90 hours on it was always pulled over as part of the pre flight and always had even compressions, until today. It had 3 good and one very poor so I didn't fly.

 

I checked the valves and 3 were a bit wide, so I re adjusted them and the compressions were the same. 1 low.

 

I then did a ground run, just skipped it along at T/O speed and the revs were good, it ran sweetly as usual at slow speed and when I pulled it through after stopping it I had excellent compression on all 4 cylinders. Tomorrow will tell, but it looks as if I had a sticking valve.

 

My real fear was that I would find a valve with no clearance, which would suggest a stretched valve. Tomorrow will tell and I will keep you informed.

 

 

[Yenn]

Update on yesterdays post.

 

I checked and found one of the re set valves was now tight. The compression felt good. I had expected all 3 would have been tight. I reset that valve and flew. Everything went well, engine sounds sweet and runs smoothly. I am assuming that I had a stuck valve and would not have known anything about it if I didn't always pull through compressions as part of my preflight.

 

 

[Guest shadey]

I have about 80 hrs on my 2.2 h/valve motor in my lsa jab,,every time i pull the prop through before cold start ,,i get a mixed lot of pressure responses but no hissing,,it does it now and again no matter how many times i pull it through,,motor runs very well,,,john

 

 

[Yenn]

shadey.

 

Have you talked to Jabiru?

 

They may gave some info and in any case it doesn't hurt to let Rod or Don know. It may even have some bearing on your warranty. By h/valve do you mean hydraulic tappets, they could be the cause, due to leak down while the engine is not running and pumping up as it starts.

 

 

[facthunter]

Hydraulic lifters.

 

Ian , I think they ( the cam followers ) are from an automotive source. My only experience of "pumping up" is at high revs, and they were considered unsuitable for racing purposes for that reason. IF the internals of the lifter are such a poor fit,or contaminated with foreign material, that they leakdown, and develop excessive clearance, you would hear the irregular beat on start-up and there would be a danger of the push rod moving off its ball end/or bending. I would consider a follower that behaved like this as unserviceable. It is possible that the lifters are so good at holding the hydraulic lock that when the engine cools (and contracts) the valves are held off their seats marginally, giving the symptoms of poor compression with a cold engine, that seems to be reported. Once the engine has been run, the problem seems to diminish, as the valves settle in to the normal running clearances, (virtually zero lash). Nev

 

 

[Guest shadey]

Yes Ian it dose have hyraulic lifters,,I just got out of it now,,did an hour around wentworth (near mildura) it did exactly the same again,,the 4th flip of the prop seemed the worst,,so I did it again and it seemed better ,it flew beautiful,,I think nev might have the right answer,,cheers john

 

 

[Geoff]

In this case it, (Shadey) may have had to much port the night before. :star::star: G'Day Mate

 

 

[BigPete]

G'Day Geoff - much rain up your way?

 

We've had 50 mm - did Cliff get away OK to go home or is he staying 'tll tomorrow?

 

regards

 

 

[Guest disperse]

I'm not an owner or a person with lots of jab experience. But also to the other mentioned things. I would think that the speed of the pull through could create a difference in compression pressure. ie: it would be expected that each pull through would be at a slightly different speed.. also if you start the pull through with the piston say 1 inch higher then the one before. you would feel the difference. unless you a looking at timing marks it would be easy to be off bottom dead center at the start of the pull.

 

 

[Geoff]

G'Day Peter 22 mm Cliff still hear today had to go over to Wenty to get the asic card **** done again 2years gone all ready and another $110 had to do it all again not just apply for a renewal:angry:

 

 

[facthunter]

Feel.

 

Disperse, there are bound to be variations, but as in all things, once you get the "knack" and the feel for what is right and what is not so right, you know what to expect, and get something from it.. Nev...

 

 

[BigPete]

Thanks Geoff - We had 72mm here in town.

 

Slow steady rain that soaked in and didn't run off. ;)

 

Sorry to hear the ASIC is such a pain in the A%$#.

 

regards

 

 

[Ross]

Hi Peter

 

Attended a wedding in Eltham over the weekend and heard vague reports of flash flooding around your area so returned to Leeton via the freeway as far as Benalla and then Tocumwal on Sunday afternoon. We found 18.5 mm in our gauge when we got home to Leeton just on sunset.

 

Regards

 

 

[Admin]

Ross - Eltham is right next door to me - why didn't you drop in for a coffee?????

 

 

[BigPete]

G'Day Ross - we got 72mm in our rain gauge here in town (Echuca). ;);) Lake Cooper has water in it (been empty and bone dry for about 8 years). Lots of water laying around and local grass strips closed. We don't care!!:big_grin::big_grin:

 

regards

 

 

[Ross]

Hi Ian

 

Thanks for the invite - but if it were not for the GPS I would probably be still down there driving around arguing with my wife looking for Eltham. As it was I am fairly certain that we seemed to be driving around in almost circles each side of a valley.

 

We stayed at the Gateway Motel up near Research, the wedding and reception was at Montsalvat Eltham, and the barbecue lunch on Sunday seemed to be across the valley from Montsalvat as was the shopping centre that I had to visit with my wife.

 

The 1984 street directory of Melbourne and the total overcast did not help with my lack of orientation and setting the GPS with "track up".

 

Regards from a very infrequent visitor to Melbourne.

 

 

[facthunter]

Whether compressions?

 

Hate to be a pain in the butt, BUT this thread has gone off topic chaps. Nev..