I am currently modifying my Honda Gx390 engine to run off of hydrogen. I will have to redesign the top of the engine to allow fuel injectors. One of the drawbacks to hydrogen is since it is so tiny it can fit through cracks really easily. Therefore I wanted to make the piston hold 5 rings. However, since the stock piston only allows 4 rings I would need to replace it. The problem with this is that I remember reading somewhere that crankshafts are calibrated to their piston's weight, so by replacing it I am afraid I will put unnecessary stresses on the engine. The Gx390 does come with a counterbalance in the main body so I don't know if it's the same. Any help is much appreciated. Thank you
Piston and crankshaft
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Hi. I would state that hydrogen instead of gasoline is of no concern in the cylinder. Hydrogen at high pressure is a pain to keep without leakage, migrates even through solid stainless steel, but this is not the state in the cylinder. There you will have, in practice, the same conditions as with normal fuels. Everything upstream the injector will however be a challenge.
Thank you for your responce. That saves alot of time and money lol thank you.
Changing the weight of the piston will change the balance characteristics.
The primary imbalances (from the piston moving up and down) are generally handled by the crankshaft counterweight. These are most noticeable as up and down shake at 12:00 and 6:00 in a single cylinder vertical engine.
The counterbalance shaft and its eccentric weight is to help cancel the secondary imbalances that come from the crankshaft counterweight and conn rod big end swinging around and are most noticeable as rocking around the crankshaft centerline at 9:00 and 3:00.
The primary imbalances (from the piston moving up and down) are generally handled by the crankshaft counterweight. These are most noticeable as up and down shake at 12:00 and 6:00 in a single cylinder vertical engine.
The counterbalance shaft and its eccentric weight is to help cancel the secondary imbalances that come from the crankshaft counterweight and conn rod big end swinging around and are most noticeable as rocking around the crankshaft centerline at 9:00 and 3:00.
Never seen an engine with 4 rings(at least, not in the last 50 years or so) ....I think you'd better look again.
Unless you count the two part oil ring as 2 rings, but not a normal practice.
Overall, the idea is hardly worth the effort, especially on an old bushbasher stationary engine given the (so far) problems you haven't thought about.
Hi, Simply "don't do it".... because:
The set of piston rings are not a perfect seal, and adding rings is virtually no benefit anyway.
The top 2 rings in conventional engines are "compression rings" - deemed adequate to prevent enough leakage so you develop the compression to start the engine at the lowest crank speed. They also reduce BLOW-BY gases (from the high pressure during combustion) to acceptable levels. The bottom ring is an OIL CONTROL RING: This keeps out almost all the oil from getting from below the piston to the combustion chamber, where excess oil would drain the engine too quickly, and also polute the exhaust stream - which in car engines has acatalyst that gets fouled with and metal molecules from the additives in the oil. )Hence the limited life on many cars of over 80,000 miles before you need to fit a new one)
When the engine is running, the compression can be achieved with one or no compression rings, but Blow-by is increased, which is a loss of power and efficiency from the engine. Considering that at the end of the compression rings there is a gap maybe 0.001" to 0.003" wide (to compensate for differential expansion of the cylinder and piston at varying temperature during warm-up etc.) trying to prevent hydrogen molecules from escaping the combustion chamber is a waste of time and effort.
I hope this helps your understanding?
It is actually quite complex engineering - best left to Mr Honda et al, as I know they have expert engineers whose whole task is Piston ring sealing, etc.
Good luck with the H2 conversion,. I shall be pleased to hear more.
K2
The set of piston rings are not a perfect seal, and adding rings is virtually no benefit anyway.
The top 2 rings in conventional engines are "compression rings" - deemed adequate to prevent enough leakage so you develop the compression to start the engine at the lowest crank speed. They also reduce BLOW-BY gases (from the high pressure during combustion) to acceptable levels. The bottom ring is an OIL CONTROL RING: This keeps out almost all the oil from getting from below the piston to the combustion chamber, where excess oil would drain the engine too quickly, and also polute the exhaust stream - which in car engines has acatalyst that gets fouled with and metal molecules from the additives in the oil. )Hence the limited life on many cars of over 80,000 miles before you need to fit a new one)
When the engine is running, the compression can be achieved with one or no compression rings, but Blow-by is increased, which is a loss of power and efficiency from the engine. Considering that at the end of the compression rings there is a gap maybe 0.001" to 0.003" wide (to compensate for differential expansion of the cylinder and piston at varying temperature during warm-up etc.) trying to prevent hydrogen molecules from escaping the combustion chamber is a waste of time and effort.
I hope this helps your understanding?
It is actually quite complex engineering - best left to Mr Honda et al, as I know they have expert engineers whose whole task is Piston ring sealing, etc.
Good luck with the H2 conversion,. I shall be pleased to hear more.
K2
Bentwings
Well-Known Member
I too don’t think the hydrogen will be a problem . I’d also skip the 4?ring piston for the same reason given if you really want to complicate things you could make provision forevs dyke ring but just making the ring would be a challenge . We have used these on race cars for years . They are stainless with coating and require fine cyl finish. But some of the conditions we have used them go against all the rules.
We have even run nitro engines with broken rings as there weren’t any good ones in the spare parts box . I wouldn’t worry about crank balance unless you radically change piston weight even then unless you have precision balancing equipment there is little you could do .
