Engine life for Air vs liquid cooled

Message

Gummiente · Tue Jul 11, 2006 12:26 pm

MotoF150 wrote:on ur Harley the plug fires when the piston is almost at the bottom of the cyl. You see? When that plug fires and ignites the hot gases it also heats up the whole exposed cyl cause the piston is almost at its lowest postion, that inturn causes the engine to run very hot cause the heat spends more time in the cyl before the piston reaches tdc and opens the exhaust valve and releases the hot gases, thats why Harleys overheat, run hot and have engine problems.

Thanks for the laugh!

Kal · #32 Unread post by **Kal** » Tue Jul 11, 2006 12:40 pm

I'm having difficulty with this...

As I understand the basics of internal combustion engines...

The piston compresses the gas and petrol in the cylinder as it rises. The ignition sets off the compressed mixture in a controlled explosion. The explosion forces the piston down the cylinder. The bottom of the cylinder is connected to the crank which is forced to turn by the force of the piston coming down.

If though the ignition were at the bottom of its travel inside the case then the petrol/air mixture wouldn't be under compresion and more importantly the cylinder wouldn't be forced down because its already at the end of its travel! Which in turn means that the crank dosn't turn.

Am I getting this right moto? You honestly believe that Harley's do this?

dieziege · Tue Jul 11, 2006 12:50 pm

He's saying that harleys fire before top dead center, not after it. In other words during the compression stroke while the piston is moving up.

To acknowledge the kernel of truth in that lump of krap, Harley engines DO fire before top dead center... ALL properly tuned engines do because it takes a certain amount of time for the fuel to finish igniting... you don't want to waste part of the power stroke waiting for your fuel to start burning so you fire early. By the time it reaches TDC it's fully engulfed and you have the full power stroke to tap the released energy.

As to how far before TDC, I don't know how many degrees but you can bet it ain't much because if you fire too early the engine spins backwards. Beyond faulty kick starting with the manual mentally challenged set wrong I haven't heard many credible stories of Harleys suddenly deciding to head backwards at 50MPH... which is a shame now that I think about it because they'd be very funny stories indeed... so I don't think there is much evidence to back his claim. Of course it take 2.7 seconds to refute his claim with a timing light...or by looking at whatever they have as a distributor... but that's no fun.

ZooTech · #34 Unread post by **ZooTech** » Tue Jul 11, 2006 1:05 pm

dieziege wrote:He's saying that harleys fire before top dead center, not after it.

MotoF150 wrote:on ur Harley the plug fires when the piston is almost at the bottom of the cyl. You see? When that plug fires and ignites the hot gases it also heats up the whole exposed cyl cause the piston is almost at its lowest postion, that inturn causes the engine to run very hot cause the heat spends more time in the cyl before the piston reaches tdc and opens the exhaust valve and releases the hot gases

No, he's saying the plug doesn't fire until the piston is almost at BDC on the combustion stroke, causing a massive explosion in the cylinder. He goes on to say the exhaust valve doesn't open until the piston is nearly at TDC.

He's a troll. Quit arguing with him from a logical and factual standpoint.

dieziege · #35 Unread post by **dieziege** » Tue Jul 11, 2006 1:09 pm

I've re-read that twice now an I still say he's sayin' what I sez he's sayin...

But you are right... I'm trying to make order from chaos... never wise policy.

flw · #36 Unread post by **flw** » Tue Jul 11, 2006 1:12 pm

From reading the responses, it seems to be a lively point.

So based on the responses, I assume the following for a person with no rebuild experience:

Better to buy a used water cooled bike than a air cooled, unless you have the money to pay someone to possibly rebuild it for you. This is because you never really know how previous owner drove the bike during high temps.

I didn't see anything on V design vs I design. Other than smoothness, is there any difference in life or power?

On Oil type, synth is clearly the leading way to go, if the bike can handle it. I'm thinking of older bikes/motors (seals or valve train, etc... tolerances)

Thank you all for you excellant post. I'd appreciate any more info you could pass on to a newbie.

Dan O.

MotoF150 · #37 Unread post by **MotoF150** » Tue Jul 11, 2006 1:14 pm

I don't like Harleys and I don't like anybody that owns one!

ZooTech · #38 Unread post by **ZooTech** » Tue Jul 11, 2006 1:20 pm

dieziege wrote:I've re-read that twice now an I still say he's sayin' what I sez he's sayin...

MotoF150 wrote:A Harley engine is designed by retarding the timing

the plug fires when the piston is almost at the bottom of the cyl.

When that plug fires...the piston is almost at its lowest postion

It sounds like you're giving him credit for actually knowing when the plug fires. I don't see where you're getting "plug fires just before TDC" from the above quote.

Of course, I don't exactly feel smarter from interpreting the ramblings of a mentally challenged.

dieziege · #39 Unread post by **dieziege** » Tue Jul 11, 2006 1:21 pm

flw wrote:From reading the responses, it seems to be a lively point.

So based on the responses, I assume the following for a person with no rebuild experience:
...

Actually I'd say...

Used bike... doesn't really matter whether it is air or water cooled. Both can be abused (water cooled engine could've been filled with pure water, which causes corrosion et cetera) and either can been overheated in traffic with bad results. Even if each passes a visual inspection they are probably equally likely to have hidden defects.

V engines typically deliver more of their power at lower RPMS (they have more torque)... Inline engines tend deliver their power at higher revs... net result is that if you keep each below say 5000 RPM a 100HP I-4 may actually deliver 40HP while a 70HP V-2 may deliver 70HP. Note however that this is more true for current engines than older designs... in the 70s engine designers didn't know that you needed a V-twin for torque or that an I-4 was supposed to be anemic until it hit 9000RPM so an '80 I-4 might very well put out 50FP of torque and redline at 8,000RPM... numbers currently associated with V-twins.

Synthetic oil is the way to go.... and unless something was very wrong and the engine was abused chemically it can deal with current synth oils.

Zoo... you're right... not good proof of our intelligence any way you cut it.

Kal · #40 Unread post by **Kal** » Tue Jul 11, 2006 1:24 pm

Shut up Moto, you were making sense a couple of days ago try not to post anything until you are making sense again...

Watercooled V's Aircooled (ignore moto)

Aircooled are easy to work work on and more simple designs - Watercooled can get horribly complicated, run at higher temperatures and offer a greater range of design solutions to Bike manufacturers.

As an operator there isnt much too choose from, although personally watercooled makes me nervous as its more systems that can go wrong.

It's kind of like the shaft/chain/belt drive debate.

V twins tend to have a load of torque but generate less bhp than the equivilant inline 4, which is why WSB is looking at giving Ducati and other Vtwins a 200cc advantage next year.

The Synth/dino oil debate is still ongoign and probably will be for all time.

I think you are worrying too much. Find a bike you like.