Hot rear cylinder example Jabiru 3300A-2575 and plenums

[RFguy]

and the exhaust stems will expand also-  Quite a temperature rise...  they will lengthen. 

 

valve stem material is exotic. wonder what the temp coefficient is.

Maybe I will put one in an oven (thanks Mark D for those)  and measure the TC. And the valve over its length may vary in material used.

 

Jabiru cold clearance is only specified for Solid Lifters - 0.25 to 0.3mm. that's probably a reasonable aiming point if lifters are fully compressed

[Bruce Robbins]

Glen,

It is quite a common problem. Don't risk running with little clearance.

 

Jabiru supply two different length pushrods. Measure yours and contact them.

 

You can also shorten the pushrods by removing the ball ends and machining the tube.

 

I've also heard a few "clattery" Jab motors which i think have the opposite problem. Too much gap for the lifter to take up.

 

On the last engine we did a top end on we ended up with 10 standard pushrods and 2 short pushrods. 

[facthunter]

Equating solid lifter 'clearances " with the hydraulic one s is ignoring how the hydraulic ones work. It's limiting and establishing the working range of the installed lifter and it generally going to operate for the time between the head being serviced. Mostly they stay pumped up and the oil in the lifter being hydraulically locked makes and adjusts the clearance which is virtually nil when the engine is running. The only time you will run out of adjusting ability is if something has altered enough to run out of the range of the lifter to compensate.  The engines oil pressure just supplies the oil to the lifter  and keeps it filled. If you get air in the oil it may start clicking. Failure of the lifter's internal valving may give the same symptom or having grunge in the oil..  I don't particularly LIKE hydraulic lifters as it can mask problems and also create problems as I had with a Continental 0-300 where one didn't stay pumped up and I also know of an engine failure in a 912 for the same reason. These are partial failures usually resulting in no further engine damage  but they are performance reducing  to the extent the motor will struggle to hold level flight.  Nev

[RFguy]

Hi Bruce, thanks for the comments . Well, this stuff it is all part of my aircraft engine apprenticeship... 

 

Removing ball ends and shortening. are the ball ends press fitted onto the shafts ?

[RFguy]

Nev, sure it is  not the same , but I would consider the cold solid clearance a good guide to what the clearance should be on the hydra when the hydra has run out of self-adjustment room .  IE fully compressed, there is NO room for say pushrod or stem expansion, beyond the full compressed stop in the lifter means the valve wont close. (you know this) .. that's really the place where the solid lifter is. 

[facthunter]

Alloy push rods are bad enough already. don't muck with them. If there's 2 lengths try that ex factory  They are usually press fitted ends.The steel ones often have a hard ball welded in TIG?  Much better er.  Nev

[facthunter]

 Usually everything wears to requiring   reduction of  the length and then the valve rides and doesn't seat and won't last long and maybe the head will break off as it over temps.. IF you set it up with a minimal clearance that situation will happen sooner..  Nev

[RFguy]

OK, I see what you mean. why set up with only 0.25mm in hand when there is a good 0 to 3mm of self adjustment in the lifter ....., well there's about 3mm roughly of squeeze in the lifters to the stop point, so I would think 1mm there which is ~ 1.7mm  at the valve stem would be reasonable.  I'll need to do the expansion calcs on the push rods, cylinders, and valve stems to come up with a educated answer. 

 

BRUCE what do you like to see in available 'lifter stop' clearance ?

[facthunter]

The more you allow the worse the effect will be IF the lifter fails. That's the other side of the coin.  There's a chance if the pushrod is flopping around it may move sideways out of the ball end and want to open the valve more and may bend. Even having only one cylinder (of the 6) affected in the 0-300 there was no way it would climb. Fortunately It rectified itself when I got to down about 10 feet above a sea of big tree stumps that had been cut but not cleared from the climb out area where the strip ended... Not an  ideal place to land . Nev

[RFguy]

well the book says they recommend 215mm long push rods now, mine are 217mm .  (!) 

 

I think 215 would be too short in my system considering your comment that too long and the push rod will float around in event of a lack of lifter expansion.

 

[facthunter]

Have you found a good way to depress the lifter fully.? It's easy when they have no oil in them.  If there's still play when the lifter is fully extended that is no good.  The follower can then be off the cam profile which  will reduce lift and also have a sudden initial movement. Nev

[RFguy]

they have no oil or little oil right now. sump empty. well was until I filled it with the 100 before I tidied up. might have been easier to not have any galleries with oil in them during trouble shooting. 

 

Leaving the prop in a position of lift for 20 minutes seemed to bleed them down.

 

The lifter can be compressed to its stop at the moment by pushing hard on the rocker end of the pushrod (or just the pushrod without the head on ) . when pushed all the way in, some have about 0.5mm to 1mm  clearance on the valve.  average 0.3 I think. some  0.0.... (valve not actuated JUST but lifter all the way in. )  . That's no good. hence all this discussion.

 

IE they never ever get fully extended, they're operating between their compressed stop and about a 0.5mm expanded from  that. 

 

 

Edited April 26, 2021 by RFguy

[Bruce Robbins]

Hi Glen,

The ends are pressed in. They can be removed if you are carefull, but I have never attempted to do so, though I have seen it done. I measure all the pushrods lengths before assembly.

 

Assemble the heads to the barrels and torque down with NO oil in the lifters so you can compress them easily. Take note what length pushrod went you used. Push down on the rocker at the pushrod end and measure the tappet gap with feeler guages.

 

The lifters have a working range of 3mm from memory, and I can't remember what that translates to at the tappet end. The idea is to get the lifters somewhere near middle of range if possible. From memory on the last one we did I had about 80 thou as the largest tappet gap with the lifter compressed. Others were zero or close to it.

 

That's when you get to pull a whole lot of heads off again and swap pushrods around till you're happy that all cylinders have reasonable tappet clearances. If you have already filled the lifters or turned the motor over and pumped up oil pressure, you may need to remove the lifters and pump them on the bench to empty the oil. Some of them seem very reluctant to push down by hand once in the engine and full of oil. They probably bleed down under running loads, but unless you make a tool to compress then insitu, they can be hard to do by hand.

 

Just as an aside, I have seen a Jab engine fire up and the stop after 1-2 seconds with zero compression. The oil pressure was way above spec, and had pumped all the lifters straight up to max length. Took about two hours for them to bleed back down and get the compression back.

[RFguy]

Bruce, thanks for the time taken to write the detailed information. Yeah now I have dropped some 100 into the sump, I'll remove the filter for the moment.  can run of course forward/backward to avoid oil pressurizing in the galleries.,

 

yes 3mm it is. translation is roughly x1.7 I think

 

My rods were very close to one another in length. damn close. sounds like I should pull it all apart and measure, catalog and bin them into the  various bread loaf tins (like a histogram)  for length. doesnt take long.  I've found after a few you get a knack for lining up the push rod tubes. 

 

Interesting about the over-pressure causing trouble.  

 

Do the springs ever fail in the Jab hydra  lifters? I gather there is a spring in there .

 

-glen

 

[facthunter]

If your engine  backfires , sometimes the valve(s) will be displaced from the seat and pump up so as to not close for a few minutes and will do a steady misfire until things sort themselves out. This is about the only time an engine can "fix "itself but I would still check it as soon as possible. If you have height reducing the power will lower the loads on the mounts etc and reduce vibration.. Nev

Edited April 26, 2021 by facthunter
more content.

[RFguy]

That's gold Nev, I have heard that symptom described in two instances. It rights itself with a bit of time. 

[Bruce Tuncks]

Interesting, but the main thing I have got is to be grateful for the old solid lifters in my engine. Sure they need checking, but the need for an adjustment tells you stuff.

Can you chuck out the hydraulic ones?  My guess is that other things were changed to suit the hydraulic lifters and this would be a risky thing to do.

[Old Koreelah]

30 minutes ago, Bruce Tuncks said:

Interesting, but the main thing I have got is to be grateful for the old solid lifters in my engine. Sure they need checking, but the need for an adjustment tells you stuff.

Can you chuck out the hydraulic ones?  My guess is that other things were changed to suit the hydraulic lifters and this would be a risky thing to do.

I have hydraulics and sure don’t miss the regular adjustments of tappet clearances. That exercise is good at keeping you in touch with how your engine is trending, but my preflight prop pull-throughs (I like to do ten blades on my 4 cyl.) give me a feel for how it’s going. 

[facthunter]

Different cam profile in respect of the hydraulic lifter AND the roller . Also the hydraulic lifter often uses stronger valve springs. Solid lifter with rollers would be my preference. i don't mind adjusting valves manually. You get to know if anything is going wrong. Nev

[RFguy]

well, anyway, I need to take 0.25mm off  some of  my push rods to get about 0.4mm at the valve stem fully compressed.

going to investigate a little more the varying depths of rocker sockets, see if I can reduce the number of short rods required. 

[facthunter]

I don't know what hardening is done to them. IF it's nitrided you are through it.  Nev

[RFguy]

yeah. will need to remove the ball end, file down the tube a little, and then replace the ball end. fortunately , the ball ends are not in tension, apart from some light surface tension of the oil. 

[facthunter]

I've shortened a lot of pushrods that way  but I wonder if the "already used" size has the original interference, more so with aluminium tube.  Nev

[Bruce Tuncks]

RF guy, don't you need to shorten the pushrods by 1.5mm so as to put them halfway through the 3mm adjustment of the hydraulic lifters?

 

[RFguy]

The case of  if the lifter fails ( and receeds to the bleed compressed point) there may be 1.5mm of gap between the  socket and the ball arm. As Nev points out, that could be enough that the rod ball end  comes out of the rocket ball socket. 

 

Really there just needs to be enough to take care of expansions between cold and hot.

Wear of the rocker bush will increase clearance. (I replaced bushes and lost clearance) .

Wear of the rocker tappet point will increase clearance. 

 

let's look at differential expansions : 

 push rod  15C to 90 C will expand  0.211mm  (reduces clearance) 

Cylinder bore   15C to 180C will expand 0.229mm  (increasing clearance )

Hot Head will expand ~0.1mm (increasing clearance )
oil temp Case will expand reducing clearance a little.  (reduces clearance) 

**....all in all I dont see there's much of a net change.**

0.3mm of bled clearance would yield about 0.5mm at the valve stem .

That's my target.

Anyone think I have made/making a gross error ?

 

Is there is other bad behaviour that I dont yet know about with roller hydra lifters ?

 

 

-glen

 

 

Edited April 27, 2021 by RFguy