How tight is your Jab 3300 Hot vs Cold

[Thruster87]

Just wanted to hear from other Jab 3300 owners on what it feels to rotate the prop cold and hot.How much compression kick back.Mine gets fairly tight hot vs cold very little kick back if any. Cheers

 

 

[facthunter]

Don't confuse stiffness with compressions. it's good to know what "proper" compression feels like, because I have always recommended doing it at least before the first flight. If it doesn't feel good let it idle slowly a bit of time after starting and see if the idle is even. test the feel again after the engine has been run. The after hot run test is more valid as engines that have sat for a while might not show good compression initially. Although these engines do not normally kick while hand propping excercise caution anyhow. Sometimes a cylinder will have more compression in one direction than the other. The position of the ring slots will cause that. They move around in use so don't be perturbed. Nev

 

 

[Sapphire]

Nev said: The position of the ring slots will cause that

 

Actually I read a comprehensive, scientific article on that whether the position of the ring slot position makes a difference. It was concluded that it didn't. However every car manual has you put the ring slots in a particular place. If they rotate, why bother in the first place. One of the smol [sweet mysteries of life]

 

 

[Guest Andys@coffs]

Mine has fantastic compression after its been run and poor when cold. Dont read into that thats its as it should be, its just how mine is

 

Andy

 

 

[Sapphire]

Mine has fantastic compression after its been run and poor when cold. Dont read into that thats its as it should be, its just how mine isAndy

 

Yours is just like every other engine. If by some weird circumstance you have max compression cold, you have problems.

 

 

[geoffreywh]

My engine has a real plop when turned over cold, but is stiff to turn over when hot...? can't really say why. It has to be piston/ring related, But it's not jab3300? sorry

 

 

[Sapphire]

My engine has a real plop when turned over cold, but is stiff to turn over when hot...? can't really say why. It has to be piston/ring related, But it's not jab3300? sorry

All the moving parts in your engine expand when heated so it runs tighter. If the engine runs too hot, the engine seizes up because it is too tight.

 

 

[facthunter]

The position of the ring slots DO make a difference to the holding of compression and the side the piston has moved to because of the direction of rotation. I'll bet my house on it. It may not significantly affect HOW well the engine runs. Why you would bother to stagger the oil rings ( which does not hold compression at all) eludes me. Model aeroplane engines that have piston rings which are not pegged because those engines have gridded ports to stop the rings popping out. Sometimes the engine will have poor compression and other times feels totally different. You can look into the ports and see where the ring gaps are ( or are not). When I assemble a new motor I usually stagger the compression rings only . Generally there are only two so they go at right angles at 90 degrees to the gudgeon pin . That is not critical but I do it that way. Oil plays a big part in sealing piston rings. Very fierce oil ring action could play an adverse part here. Nev

 

 

[Sapphire]

Lots of conflicting info from different sources [would your really bet your house]

 

 

[facthunter]

Sure , I've built my own model aero two stroke engines, with ringed pistons. You feel the effect all the time and it is quite pronounced. Any one who has has a McCoy, Dooling or ETA with piston rings will have noticed it. two stroke motor bike engines will have better compression in one direction than the other. They are pegged so they can't turn to a position where the ring could catch in the port. Put a spanner on the nut on the end of the shaft and try it. It's always better when the piston if forced against the bore at the same point where the ring gaps are. That way the leakage is stopped because the piston has sealed against the cylinder wall, where the gaps would have let the gas past if it wasn't. The side thrust of the conrod pushes it there, when you are turning the engine over against compression. Doesn't that make sense?. Nev

 

 

[Thruster87]

Yours is just like every other engine. If by some weird circumstance you have max compression cold, you have problems.

But I find it hard to interpret which part of the engine is causing the stiffness when hot and also what is normal due to my lack of exprience on the type.Without doing an actual compression [gauge] test hot vs cold how would you know. Cheers

 

 

[Sapphire]

But I find it hard to interpret which part of the engine is causing the stiffness when hot and also what is normal due to my lack of exprience on the type.Without doing an actual compression [gauge] test hot vs cold how would you know. Cheers

 

Compression won't tell you how stiff the engine is. The hottest parts are proboably giving the most stiffness including the aluminium piston which is expanding the most. Don't worry your little head, all the parts are manufactured so they have the correct dimentions when the engine is at normal operating temp and the engine will be more stiff. Of course if the engine is way too stiff then there may be a problem. An experienced hand will judge that.

 

 

[Sapphire]

Sure , I've built my own model aero two stroke engines, with ringed pistons. You feel the effect all the time and it is quite pronounced. Any one who has has a McCoy, Dooling or ETA with piston rings will have noticed it. two stroke motor bike engines will have better compression in one direction than the other. They are pegged so they can't turn to a position where the ring could catch in the port. Put a spanner on the nut on the end of the shaft and try it. It's always better when the piston if forced against the bore at the same point where the ring gaps are. That way the leakage is stopped because the piston has sealed against the cylinder wall, where the gaps would have let the gas past if it wasn't. The side thrust of the conrod pushes it there, when you are turning the engine over against compression. Doesn't that make sense?. Nev

 

That makes sense and so it is most likely to be true. And I was looking forward to moving into a new house:yes:

 

 

[facthunter]

I t might have had to be a modest one. Cheers. Nev

 

 

[Thruster87]

Compression won't tell you how stiff the engine is. The hottest parts are probably giving the most stiffness including the aluminum piston which is expanding the most. Don't worry your little head, all the parts are manufactured so they have the correct dimensions when the engine is at normal operating temp and the engine will be more stiff. Of course if the engine is way too stiff then there may be a problem. An experienced hand will judge that.

You're right on the money as I would like to hear from an experienced hand who can judge between normal and abnormal stiffness with these engines not the theory behind piston engines as I'm a LAME Cheers

 

 

[viewfromright]

My engine has a good compression feel when turned over cold, but is stiff to turn over when hot, and hard to pick up the compression cycles.

 

 

[nong]

I've seen plenty of Jabs get tight when hot. I had one (2200) that could not be rotated by the starter-motor when hot.......very cruel on the start system. When cold it felt good. Anyway, the valves were starting to "hiss" so it was overhauled. I think the tightness might be crankshaft/through bolt related. Maybe your crankcases are fretting.

 

 

[Thruster87]

I've seen plenty of Jabs get tight when hot. I had one (2200) that could not be rotated by the starter-motor when hot.......very cruel on the start system. When cold it felt good. Anyway, the valves were starting to "hiss" so it was overhauled. I think the tightness might be crankshaft/through bolt related. Maybe your crankcases are fretting.

It's only done 32hrs since new and 8 hrs since replacement thru bolts fitted.It appears that these engine can get quite tight once hot [spoke to Jab] but like I said earlier wanted to get a more informed cross-sectional opinion from actual /owner operators of their Jab 3300's Cheers

 

 

[RogerLewis]

But I find it hard to interpret which part of the engine is causing the stiffness when hot and also what is normal due to my lack of exprience on the type.Without doing an actual compression [gauge] test hot vs cold how would you know. Cheers

Thruster,

 

The Jabiru engine will typically get stiff when the barrels distort when hot. You can check this by carrying out the following procedure:

 

1. hand swing your prop to checking all the compressions and more importantly checking for stiffness when the engine is cold.

 

2. Run the engine for 2 mins at 1200 rpm and then shut down

 

3. Hand swing the engine again and check for stiffness.

 

if the engine feels stiffer then it is because the barrels are beginning to distort. I say this because after 2 min at 1200 rpm only the barrels get hot.

 

Rule of thumb. If you fly the aircraft and shut down always watch the prop. If it kicks back then the engine is acceptable.

 

If the engine gets really stiff then it will need remedial work. Essentially this means removing and honing the barrels and using re-worked barrel base nuts. When re-torquing, check for barrel going stiff using a hot air gun.

 

Roger Lewis

 

 

[Howatharra]

Just wanted to hear from other Jab 3300 owners on what it feels to rotate the prop cold and hot.How much compression kick back.Mine gets fairly tight hot vs cold very little kick back if any. Cheers

I've owned four Jab motors, three 2200 and a 3300. All of them were stiff when hot and behaved as you described. A friend has a 2200 in an identical aircraft but his doesn't behave that way. He used a rebuilt engine which had the old barrels re-honed which may explain the difference, i.e. more clearance for the pistons. However he uses far more oil than I do if he runs the 15W50 Shell. Recently he tried out HPR 15w60 oil and now has very little oil burn running RON 95 fuel and has picked up around 100 extra rpm on takeoff.

 

Howatharra.

 

Just wanted to hear from other Jab 3300 owners on what it feels to rotate the prop cold and hot.How much compression kick back.Mine gets fairly tight hot vs cold very little kick back if any. Cheers

[facthunter]

IF you run avgas stick to an aviation oil. If you run mogas fair enough use a good engine oil. Aircooled engines are not common, and run much hotter than liquid cooled motors Just having a thick oil doesn't mean it is a good aero engine oil. Ring groove carboning ( top one mainly) and valve stem jambing can occurr from deposit build-up , at high temps..Nev

 

 

[Howatharra]

IF you run avgas stick to an aviation oil. If you run mogas fair enough use a good engine oil. Aircooled engines are not common, and run much hotter than liquid cooled motors Just having a thick oil doesn't mean it is a good aero engine oil. Ring groove carboning ( top one mainly) and valve stem jambing can occurr from deposit build-up , at high temps..Nev

As a level 2 I get a lot of enquiries about Jab engine issues. Recently the lube oil issue seems to be a common one, possibly arising from a forum at Natfly. I have to stick to Jabiru's recommendations as an L2 and not make recommendations outside of that. However I am currently monitoring four Jab owners who have made the decision to change engine oil types. All four had experienced loss of compression after only 100 to 150 hours on new enines running the normal aviation oil. I inspected the engines after they had pulled the cylinders and found that all four engines had been fitted with what appeared to be chrome rings which had galled with the ring metal forming a fine razor sharp feather pulled upwards running between the piston and the cylinder. The ring gaps on the top ring measured in excess of 5mm in some cases which was surprising in view of the low hours. Three of the engines were 2200 and one 3300. I know the owners and they are good with their maintenance and operation.

 

I recommended that they clean the piston grooves carefully, have the bores lightly honed and checked for out of round, and re-fit using cast iron replacement rings, which all did. So far so good, all four are reporting good results and all are running the Penrite HPR 15/60 synthetic multigrade oil on Mogas. I don't know where they got that particular recommendation from. I'll be watching with a degree of interest to see how it works out long term. The longest hours run since is approaching 40.

 

Howatharra

 

 

[VFR Pilot]

The position of the ring slots DO make a difference to the holding of compression and the side the piston has moved to because of the direction of rotation. I'll bet my house on it. It may not significantly affect HOW well the engine runs. Why you would bother to stagger the oil rings ( which does not hold compression at all) eludes me. Model aeroplane engines that have piston rings which are not pegged because those engines have gridded ports to stop the rings popping out. Sometimes the engine will have poor compression and other times feels totally different. You can look into the ports and see where the ring gaps are ( or are not). When I assemble a new motor I usually stagger the compression rings only . Generally there are only two so they go at right angles at 90 degrees to the gudgeon pin . That is not critical but I do it that way. Oil plays a big part in sealing piston rings. Very fierce oil ring action could play an adverse part here. Nev

I'm a little late with this one.....

 

I have built many engines over the years and I always keep the ring gaps 120 deg apart including the 3 piece oil rings, they don't hold compression but they do hold oil.

 

I also keep the gaps away from the thrust faces as much as possible.

 

 

[VFR Pilot]

IF you run avgas stick to an aviation oil. If you run mogas fair enough use a good engine oil. Aircooled engines are not common, and run much hotter than liquid cooled motors Just having a thick oil doesn't mean it is a good aero engine oil. Ring groove carboning ( top one mainly) and valve stem jambing can occurr from deposit build-up , at high temps..Nev

Valve stems are lubricated by fuel not oil.

 

If your engine is designed to run on avgas then you should use it.

 

Avgas uses tetra ethyl lead to lubricate valves and guides, (originally introduced by Henry Tizard as an anti knocking agent which allowed for higher compression ratios). Tetra ethyl lead was replaced by Tin in modern times in unleaded fuel.

 

If you want to run unleaded fuel in your avgas designed engine then you should change your valve guides to suit.

 

 

[cooperplace]

I've owned four Jab motors, three 2200 and a 3300. All of them were stiff when hot and behaved as you described. A friend has a 2200 in an identical aircraft but his doesn't behave that way. He used a rebuilt engine which had the old barrels re-honed which may explain the difference, i.e. more clearance for the pistons. However he uses far more oil than I do if he runs the 15W50 Shell. Recently he tried out HPR 15w60 oil and now has very little oil burn running RON 95 fuel and has picked up around 100 extra rpm on takeoff.Howatharra.

wow, he picked up another 100rpm by changing from 15W50 to 15W60? that seems counter-intuitive. No other changes made?