Given the fact that standard size replacement pistons are no longer available from Jabiru USA / Arion and that their solution is to overbore all of your cylinders as a set and then install oversize gen 3 pistons with the valve relief at a cost of $1370 + shipping costs (pistons, rings and cylinder machining only and without shipping costs), I have spent a lot of time looking at alternatives.
Those from Camit, the company who behind the scenes manufactured all of the parts for the Jabiru engines for generations 1-3, have long told that the Jabiru pistons are from the 3800 Holden Commodore. Also known as the Buick 3800 series 2 engine. Some changes were made as the Buick engine retains the piston pin through a shrink fit in the small end bearing. Thus no circlips are needed in the piston itself. In the case of the Jabiru application, it must have been known that the piston runs too hot for a shrink fit piston pin, thus it was converted to a "fully floating" application and a set of circlips was used in the piston. Initially this required the pistons to be modified to accept the circlips.
Time passes and the Buick engine is of course long out of production, having lasted to 2008. Spares are now through the aftermarket and the aftermarket sells full floating pistons and non floating (with and without circlips and its all based on the fit of the pin n the small end bearing. I found that some of the well known US tuning outlets (Summit Racing in this case) carry these pistons. I had to confirm that the rings that were on offer were matched to the pistons because the data provided was appalling (dimensions of the ring grooves not provided) but as it turns out they were indeed a match. From comments on Jabiru groups who have sed Hastings rings, they are said to be better than the rings provided by Jabiru.
So I am proceeding with a rebuild of a 160 hour engine that I bought as a backup engine. I know that 1 cylinder is low on compression. I looked up the specs for the Buick 3800 engine, in naturally aspirated form they put out up to 205hp and ran up to 5000+ rpm as a push rod motor. Thats 34.1hp/cyl compared to the 20hp/cyl of the Jabiru engine at 3300rpm. From a mechanical load position, the Jabiru application is loafing compared to the original engine it was in. The main problem with the Jabiru is heat. The pistons get hot enough that oil is coked in the region of the pistons where the rings sit and that coking eventually jams the rings and you lose compression and in some cases may score the cylinders and even break the rings. Blowby will raise the oil temperature, especially at maximum power during climb, worse than it was in the first place. Heat also causes the head material to soften and for the cylinder sealing surface to plastically deform the cylinder head face which is why the head bolts constantly lose their torque and why Jabiru require that they be retorqued at every 25hr oil change. Going with liquid cooled heads resolved the heat problem for both the cylinder head and the piston as well as lowering the oil temperature. Should bode well for less coking of the piston ring grooves and longer oil life (implement oil analysis to track its condition. I live close to the only Phillips 94UL fuel sources in Michigan and intend to use it 100% for local and training flights to minimise lead contamination of the oil.
My idea is to strip this engine down completely and go through all the parts looking for any of the known problems.
Case fretting
Undersize fasteners (through bolts and cylinder bolts)
Flywheel to crankshaft attachment (inadequate torque capability)
Prop hub to crankshaft attachment (inadequate torque capability)
Main and rod bearings
Cylinder condition
Replace air cooled cylinder heads with LCH heads from Rotec
Delete muffler and reduce exhaust heat rejection under the cowl
Replace carb with throttle body
Port injection
Electronic ignition
Delete both distributors
replace 1 distributor with gear driven water pump for LCH
replace second distributor with gear driven backup alternator
Replace multi part flywheel with 1 piece CrMo flywheel. Potentially use diamond grit shim between flywheel and crankshaft for positive mechanical keying. Same with Prop flange. Both currently rely on small fasteners and friction between steel surfaces alone.
Add coolant based cabin heater, no carb heat system will be needed because of fuel injection
I am trying to get the core engine shipped to MI from AZ, freight industry seems to be in turmoil due to bankruptcies and other problems so its amazingly difficult to make this simple shipping exercise happen right now... I do have a build thread on this particular engine but dont yet have the core in my hands, but at least I seem to have found a piston and ring option.
Those from Camit, the company who behind the scenes manufactured all of the parts for the Jabiru engines for generations 1-3, have long told that the Jabiru pistons are from the 3800 Holden Commodore. Also known as the Buick 3800 series 2 engine. Some changes were made as the Buick engine retains the piston pin through a shrink fit in the small end bearing. Thus no circlips are needed in the piston itself. In the case of the Jabiru application, it must have been known that the piston runs too hot for a shrink fit piston pin, thus it was converted to a "fully floating" application and a set of circlips was used in the piston. Initially this required the pistons to be modified to accept the circlips.
Time passes and the Buick engine is of course long out of production, having lasted to 2008. Spares are now through the aftermarket and the aftermarket sells full floating pistons and non floating (with and without circlips and its all based on the fit of the pin n the small end bearing. I found that some of the well known US tuning outlets (Summit Racing in this case) carry these pistons. I had to confirm that the rings that were on offer were matched to the pistons because the data provided was appalling (dimensions of the ring grooves not provided) but as it turns out they were indeed a match. From comments on Jabiru groups who have sed Hastings rings, they are said to be better than the rings provided by Jabiru.
So I am proceeding with a rebuild of a 160 hour engine that I bought as a backup engine. I know that 1 cylinder is low on compression. I looked up the specs for the Buick 3800 engine, in naturally aspirated form they put out up to 205hp and ran up to 5000+ rpm as a push rod motor. Thats 34.1hp/cyl compared to the 20hp/cyl of the Jabiru engine at 3300rpm. From a mechanical load position, the Jabiru application is loafing compared to the original engine it was in. The main problem with the Jabiru is heat. The pistons get hot enough that oil is coked in the region of the pistons where the rings sit and that coking eventually jams the rings and you lose compression and in some cases may score the cylinders and even break the rings. Blowby will raise the oil temperature, especially at maximum power during climb, worse than it was in the first place. Heat also causes the head material to soften and for the cylinder sealing surface to plastically deform the cylinder head face which is why the head bolts constantly lose their torque and why Jabiru require that they be retorqued at every 25hr oil change. Going with liquid cooled heads resolved the heat problem for both the cylinder head and the piston as well as lowering the oil temperature. Should bode well for less coking of the piston ring grooves and longer oil life (implement oil analysis to track its condition. I live close to the only Phillips 94UL fuel sources in Michigan and intend to use it 100% for local and training flights to minimise lead contamination of the oil.
My idea is to strip this engine down completely and go through all the parts looking for any of the known problems.
Case fretting
Undersize fasteners (through bolts and cylinder bolts)
Flywheel to crankshaft attachment (inadequate torque capability)
Prop hub to crankshaft attachment (inadequate torque capability)
Main and rod bearings
Cylinder condition
Replace air cooled cylinder heads with LCH heads from Rotec
Delete muffler and reduce exhaust heat rejection under the cowl
Replace carb with throttle body
Port injection
Electronic ignition
Delete both distributors
replace 1 distributor with gear driven water pump for LCH
replace second distributor with gear driven backup alternator
Replace multi part flywheel with 1 piece CrMo flywheel. Potentially use diamond grit shim between flywheel and crankshaft for positive mechanical keying. Same with Prop flange. Both currently rely on small fasteners and friction between steel surfaces alone.
Add coolant based cabin heater, no carb heat system will be needed because of fuel injection
I am trying to get the core engine shipped to MI from AZ, freight industry seems to be in turmoil due to bankruptcies and other problems so its amazingly difficult to make this simple shipping exercise happen right now... I do have a build thread on this particular engine but dont yet have the core in my hands, but at least I seem to have found a piston and ring option.
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