weight of 4 & 2 stroke engines?

[Ariadne]

My son asked me a question this morning which I couldn't answer, which came about as we have got to replace our old Suzuki DF6 which was terminal (cost prohibitive!!!).

Why are 4 stroke engines heavier than 2 stroke engines?


Bearing in mind that our new Aquapro RHIB is only 30Kg (and rated for a 9hp engine), hasn't the engineering side of outboards lost the plot? A new 4 stroke 9hp outboard weighs in at about 50Kgs and a 15hp 2 stroke weighs in at 22Kg. Half the weight and nearly twice the power! The 4 stroke engine is nearly 20Kg heavier than the dinghy its supposed to drive, whereas the 2 stroke is 8Kg lighter.

Or, is it because the EU has banned the sale of 2 stroke engines to the general public, and the RHIB/dinghy manufacturers make/design boats for the rest of the world which still quite happily run around with 2 stoke engines?

Sensible answers & comments please.

P.S.
Outside of the Uk anybody will sell you a 2 stroke engine - we have been asked on numerous occasions whether want a new 2 stroke or 4 stroke! /forums/images/graemlins/frown.gif

 

[gandy]

[ QUOTE ]
...15hp 2 stroke weighs in at 22Kg.

[/ QUOTE ]Is that really the case? I didn't look at all makes, of course, but I looked into this recently for slightly smaller engines than you're interested in. Speaking only for Mercury their two-strokes were 5HP=20kg, 8HP=33kg. Four stroke 4, 5 or 6HP=25kg.

 

[sarabande]

2 strokes are lighter bcs (generally):

no valve train, no valves, holes (ports) in the cylinder walls, less of a crankcase full of oil, no dedicated lubrication system for the crank/ conrod/ piston bearings; fires every stroke - not just one in two; overall - less parts = less mass.

 

[Salty John]

4-stroke motors weigh between 10% and 20% more than 2-stroke motors for the reasons others have indicated.
A typical 4-stroke 15HP weighs 45kg, a typical 4-stroke 10HP weighs 40kg, and a 5HP about 25kg.

 

[seabright]

Gone back to 2 stroke as now in NZ. Feel much better. Had a Suzuki DF6 - were we unlucking or did others find this a pig of an engine? From this sample size of 1, find 2 strokes much more suited to cruisers needs so not just a weight issue with 4 strokes.

 

[Ariadne]

The Suzuki DF6 is a worthless piece of scrap metal. Has to be worst engine ever made! Too heavy, unreliable, a sod to keep serviced and you can't maintain the gear shift to keep it greased and/or free of salt, unless you remove the head.

Was never designed by an engineer just a bunch of C...ts/monkeys sorry accountants who can see money rolling in from the punters.

They should have stuck to making bikes!!!!!!!!!!!

 

[ralf2]

We were weight concious with regard to the rib and engine set up and bought a 2 stroke tohatsu 9.8.Its a devil in disguise and pushes a 3.1 avon rib with 16 stone of me and my 7 and 9 year old kids along at about 24kmph i`ll never sell it.