Is it not more common to have the gudgeon pin off centre in the piston to achieve this? If that is the situation turn the piston round.
There has been some study into the effects of offsetting the crank relative to the bore centre, maybe better economy/emissions, I can't remember?
Full Version: Running an engine in reverse, can it be done?
QUOTE (gordmac @ Sep 13 2009, 19:49) 
Is it not more common to have the gudgeon pin off centre in the piston to achieve this? If that is the situation turn the piston round.
As long as the crown is symmetrical - often not the case with valve cut outs and pent-roof chambers.QUOTE (gordmac @ Sep 13 2009, 19:49)
There has been some study into the effects of offsetting the crank relative to the bore centre, maybe better economy/emissions, I can't remember?
Reduces side thrust on the bore opposite the descending crank-pin (power stroke) since this is greater than the side thrust opposite the ascending crank-pin (compression stroke).
Also a benefit of slightly longer "dwell" ATDC than BTDC thus more combustion completed earlier in the expansion stroke.
I have just had a flashback! No, I'm OK nurse...One of the engines that I 'cutaway', and for which I had some works drawings, had the cylinder bore centreline off-set 3mm relative to the crank CL.
QUOTE (Tony Matthews @ Sep 13 2009, 20:29)
I have just had a flashback! No, I'm OK nurse...One of the engines that I 'cutaway', and for which I had some works drawings, had the cylinder bore centreline off-set 3mm relative to the crank CL.
Yes, its done both ways - offset bore and offset pin. I think the offset bore is more elegant - the offset pin creates a moment which tends to "rock" the piston.
QUOTE (Tony Matthews @ Sep 13 2009, 19:29)
I have just had a flashback! No, I'm OK nurse...One of the engines that I 'cutaway', and for which I had some works drawings, had the cylinder bore centreline off-set 3mm relative to the crank CL.
3mm is not a lot. Some Honda inline fours use as much as 13mm. The Ford flathead V-8 had better than a quarter-inch of crank offset, .265 in to the left if I recall.
In some V-type engines the crankshaft CL is above the geometric intersection of the two banks.
QUOTE (McGuire @ Sep 14 2009, 07:53)
3mm is not a lot. Some Honda inline fours use as much as 13mm. The Ford flathead V-8 had better than a quarter-inch of crank offset, .265 in to the left if I recall.
In some V-type engines the crankshaft CL is above the geometric intersection of the two banks.
In some V-type engines the crankshaft CL is above the geometric intersection of the two banks.
Pretty sure the latter applies in some motorsport we used to watch on TV. The difference between gudgeon pin offset and bore offset, for production cars is that you can tune the former right through the development process, the latter is pretty much fixed. I don't know whether the trade-offs are different (fairly sure they are), as you probably know piston manufacturers are damn good at minimising piston slap and piston friction, they tend to send along a box of bits and say try them rather than explaining what they've done and why.
The MGA Twin-Cam had offset Rods,1 set for 1 & 3 and the other for 2 & 4, not sure of the consequences(if any) of this over the normal B-Series Rods.
OT slightly,the UK "Frisky" got a mention in a local paper this Week, it also had the Villiers 2-stroke that gave it 4 reverse gears and apparently was the forerunner/related to the Australian Ligtburn Zeta.
"Frisky" Bubble Car.
OT slightly,the UK "Frisky" got a mention in a local paper this Week, it also had the Villiers 2-stroke that gave it 4 reverse gears and apparently was the forerunner/related to the Australian Ligtburn Zeta.
"Frisky" Bubble Car.
QUOTE (Ian G @ Sep 15 2009, 10:06)
The MGA Twin-Cam had offset Rods,1 set for 1 & 3 and the other for 2 & 4, not sure of the consequences(if any) of this over the normal B-Series Rods.
That would be an axial offset - the type of offset we are talking about can't be achieved by modifying the rod. The other variable on the MG would be the angled big-end split.
Lampredi's Fiat twin cam can be made to run in the reverse direction.
Many years ago I had the idea of using a rear engine Fiat inline four in a mid engine application. I figured if I replace the timing chain and sprockets with timing gears, turned around the flywheel gear and moved the starter to the other side of the flywheel, the bottom end would rotate in the other direction while the cam and distributor would retain the original rotation. I was just a kid then and gave up after trying to band saw and file the timing gears out of aluminum plate.
QUOTE (Greg Locock @ Sep 14 2009, 09:55)
Pretty sure the latter applies in some motorsport we used to watch on TV.
Undoubtedly.
QUOTE (McGuire @ Aug 26 2009, 11:40)
Quite so... all the original GMC (aka Detroit) Diesels were modular in design so the same basic engine could be installed front-to-back or run in either direction. (The Allison V-1710 was also laid out in this manner.) Buses with 4-71 or 6-71 engines were configured to run in either direction, depending on the type of driveline used. A pair of 12-278 or 16-278 engines side-by-side, running in opposite directions, would be a very common marine installation. On smaller craft, a pair of counter-rotating 6-71s.
However, the original GMC diesel nomenclature created some confusion. Throughout the industry, "standard rotation" is held to be CCW as viewed from the flywheel, which GMC termed CW as viewed from the front pulley. Same rotation, opposite description. So a standard GMC engine would be called "right-rotation," which was really left.
... when you buy a pair of larger outboard motors (~140 hp up) you can spec them as a matched, counter-rotating pair. Their power heads rotate in identical direction, while their lower units output in opposite (away) directions. Not as critical in lower output installations -- the difference in handling is apparent but not objectionable.
Counter-rotating engines in twin-screw boats have fallen away in recent years -- as engines have become more sophisticated, they have become more difficult to convert. Meanwhile, there are far more options in outdrive systems than in past years. Still a lot of them out there, however.
In decades past there were a number of single-engine power boats that employed automotive engines converted from standard (CCW) to CW rotation. Chris-Craft, Century, Correct Craft, to name a few... and there are still many of those around, too. Over the years I have heard many explanations as to why this was done, some of them downright convincing. Among other things, it is said that serious water skiers preferred them. Correct Craft ski boats commonly employed a single Ford V8 converted to reverse rotation.
However, the original GMC diesel nomenclature created some confusion. Throughout the industry, "standard rotation" is held to be CCW as viewed from the flywheel, which GMC termed CW as viewed from the front pulley. Same rotation, opposite description. So a standard GMC engine would be called "right-rotation," which was really left.
... when you buy a pair of larger outboard motors (~140 hp up) you can spec them as a matched, counter-rotating pair. Their power heads rotate in identical direction, while their lower units output in opposite (away) directions. Not as critical in lower output installations -- the difference in handling is apparent but not objectionable.
Counter-rotating engines in twin-screw boats have fallen away in recent years -- as engines have become more sophisticated, they have become more difficult to convert. Meanwhile, there are far more options in outdrive systems than in past years. Still a lot of them out there, however.
In decades past there were a number of single-engine power boats that employed automotive engines converted from standard (CCW) to CW rotation. Chris-Craft, Century, Correct Craft, to name a few... and there are still many of those around, too. Over the years I have heard many explanations as to why this was done, some of them downright convincing. Among other things, it is said that serious water skiers preferred them. Correct Craft ski boats commonly employed a single Ford V8 converted to reverse rotation.
Surely most boats adjust the rotation with the gearbox. Most are simply a forward/neutral/ reverse box, so all you have to do is reverse the cable system on the box.
I once helped a fellow fit a new prop on his dive boat. He had a new pair of props and picked up the wrong one. Tries to leave the dock the following day and promptly rams the dock with the stern. So he spent the day with one gear lever forward and the other in reverse and we got to do the prop swap again that afternoon.
QUOTE (JtP1 @ Sep 16 2009, 06:47)
Surely most boats adjust the rotation with the gearbox. Most are simply a forward/neutral/ reverse box, so all you have to do is reverse the cable system on the box.
Nope. Sure, there are boats set up that way, their limitation being that forward and reverse must be the same gear ratio. With an automotive-type engine in a typical pleasure boat application, reverse is typically 1:1 while forward might be 1.5:1, for example.
There are three basic types of inboard prop drive configurations in pleasure and utility boats: direct, vee-drive, and Inboard/Outboard. All are quite common in North America. In a vee-drive boat, the engine(s) is turned around backward with the flywheel facing the bow, with a torque tube connecting to a vee-drive unit mounted forward with the prop shaft running aft under the engine. Some vee drive units incorporate an integral reverse gear while others employ a separate transmission for reverse. Some boats with vee drives, racing for instance, have no reverse. And naturally, depending on its configuation the vee-drive may reverse the prop shaft's rotation.
QUOTE (McGuire @ Sep 15 2009, 19:55)
Nope. Sure, there are boats set up that way, their limitation being that forward and reverse must be the same gear ratio. With an automotive-type engine in a typical pleasure boat application, reverse is typically 1:1 while forward might be 1.5:1, for example.
There are three basic types of inboard prop drive configurations in pleasure and utility boats: direct, vee-drive, and Inboard/Outboard. All are quite common in North America. In a vee-drive boat, the engine(s) is turned around backward with the flywheel facing the bow, with a torque tube connecting to a vee-drive unit mounted forward with the prop shaft running aft under the engine. Some vee drive units incorporate an integral reverse gear while others employ a separate transmission for reverse. Some boats with vee drives, racing for instance, have no reverse. And naturally, depending on its configuation the vee-drive may reverse the prop shaft's rotation.
There are three basic types of inboard prop drive configurations in pleasure and utility boats: direct, vee-drive, and Inboard/Outboard. All are quite common in North America. In a vee-drive boat, the engine(s) is turned around backward with the flywheel facing the bow, with a torque tube connecting to a vee-drive unit mounted forward with the prop shaft running aft under the engine. Some vee drive units incorporate an integral reverse gear while others employ a separate transmission for reverse. Some boats with vee drives, racing for instance, have no reverse. And naturally, depending on its configuation the vee-drive may reverse the prop shaft's rotation.
Sounds almost like a Countach.
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