Jabiru 3300 - Reassembly - Re-fitting Cylinder Barrels, Pistons and Thru-Bolts

Introduction ...

This page contains photos of a Jabiru 3300A Solid Lifter engine under going a bulk strip and rebuild. This page documents the process of re-fitting the cylinder barrels, pistons and thru-bolts.



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Image 1

Just to recap ... We ended the last section with the two crankcase halves together but no thru bolts fitted as yet. Here you can see we have two crankcase halves (that have already been fitted to the crankshaft and camshaft by now), cylinder barrels, pistons, thru bolts, 12 point nuts organised and barrel base o-rings all in position. We also have a new tube of Loctitie 518 at the ready.

If you look closely in this picture you will see the pistons already "started" in the base of the cylinder barrels. The piston rings have been compressed, orientated so that their ring gaps are 120 degress apart, and the piston have been have been inserted only just far enough to retain the piston rings in place. This is because the piston pin will be pushed through the small end of the conrod with the piston partially in the barrel. If we push the piston too far in the barrel it will no longer be possible to push the piston pin through.

Note that there are two physically possible orientations of the pistons. One will result in a balanced engine where the valves clear the piston crown and the thrust line offset of the piston pin is observed. The other (incorrect) orientation of the piston will result in the thrust line offset being wrong and also the valve relief cutouts on the crown of the piston will not be orientated correctly to accomodate valve travel. I have never tried to fit the piston around the wrong way to see whether or not the valves actually interfere with the pistons but I am guessing there would be problems. At any rate make sure that you fit the pistons correctly with the valve relief cutout on the side of the sump. Note also that the pistons are "handed" e.g. in a six pot engine there are three left handed pistons and three right handed pistons. All of this should have been given due consideration at the point that the pistons were weighed into reciprocating matched pairs.

It is really important to make sure that the 12 point nuts turn freely on the thru bolts otherwise the torque'ing up process will be more arduous than it needs to be. These thru bolts and nuts are to be assembled "dry". They should be a snug fit but they shouldn't be anything FOD or otherwise that impedes their even torque'ing up ...

Note that once we start the thru bolt torque'ing up process the clock is effectively ticking. The Loctite 518 cure time is shorter in the summer with higher ambient temperatures. All thru bolts and crankcase studs need to be up to target torque BEFORE the 518 has had a chance to cure otherwise a seal between the two crankcase halves and between the crankcases and cylinder barrels will not be realised ...

The entire torque'ing up process takes me in the region of an 90 minutes for a six pot Jabiru. This is the most important part of the Jabiru rebuild to get right. If the thru bolt torque's are not applied evenly and uniformly then there is risk of barrel distortion and a "tight" running barrel that may not become apparent until your engine gets to operating temperature. If the target torque for 7/16th thru bolts is 58Nm I would suggest that to avoid uneven torque'ing that it is a good idea to torque all thru bolts in stages e.g. all to 5Nm, all to 10Nm, all to 15Nm etc. and carry on in 5Nm jumps until target torque is reached. This seems to yield better results than observing a middle cylinder out torqu'ing pattern. Yes it takes longer and might seem a bit over the top but the time invested is worth it.

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Image 2

Apologies in advance - I don't seem to have taken as many photos as would have been helpful during this part of the build so I'll try and add some extra images at a later date and explain what I've missed. Here we can see that one of the middle cylinder barrels (with piston) has been offered up to the conrod and the piston pin pushed all the way home through the conrod. The second piston pin retaining circlip is being located in the circip groove. What may not be so apparent is that the cyinder base o-ring has been positioned and retained in place with an application of Loctite 518. Arrows point to o-ring. The cylinder base that butts up to the o-ring has been thoroughly degreased for a good bond with the Loctite 518 ...

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Image 3

Here is a slightly improved view of the cylinder base o-ring ...

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Image 4

The barrel can now be pushed home to sit in it's correct position on the crankcase. Holding it there with one hand we can push a thru bolt through from the other side of the crankcases and puts the 12 point nuts on the barrel end of the thru bolts as shown here. Now that barrel for cylinder 3 is now in position we can balance it out on the other side by fitting the barrel for cylinder 4 ...

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Image 5

Note the orientation of the valve relief cutouts on the piston crown e.g. they face towards the sump ...

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Image 6

Here you can see we have fitted barrels for cylinders 3,5 and 4 so far ...

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Image 7

Cylinders 3,5 and 4,6 ....

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Image 9

All barrels now in place. Up until now only enough torque has been applied to any thru bolt nuts to "close" the crankcase halves gently but no more. Now we start the progressive torque'ing up. Note that for consistent accurate torques a crowsfoot is used and set at right angles to the torque wrench ..

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Image 10

Once the thru bolts are tensioned and torque'd correctly take the opprtunity to remove the excess Loctite 518 ..

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