Full crank vs half crank

[rthacker7]

I've seen advertisements on 2 stroke engines claiming it had a full crank so it was a better motor. While I can see the 1/2 crank or what ever its called
might be a less quality motor, does the crank really define the quality of the motor or is it an indicator of going cheep?

[bgsengine]

Yes in a way - full crank can take more torque as it is supported on both ends by bearings, where a half crank has support only on one end - putting too much torque on it you can bend the crank - Many machines may be built with half crank to save space and weight (Ive seen Stihls with half cranks) it has more to do with the amount of torque that will be applied. - stick one end of a rod in a wall, and lean on it, it may or may not support your own weight.. but can't support 2 of you.. but that same rod, supported on both ends, can support a lot more weight

Most cheaper consumer models can be built with half crank, they really do not output that much torque or power for their weight and CC's (That's another reason why the CC of an engine is no longer an indicator of its true power) so they can stall out under a heavy enough load, while an *equivalent* CC's engine from someone like Echo, Stihl, etc with full crank and a little more weight, can put out twice or three times the power... So, it is not necessarily an indicator of quality, but it surely can indicate that the full crank machine is built to handle heavier loads than a similar CC model with half crank.

[NevadaWalrus]

One major downside of half cranks is the recoil starter must be on front side of engine. At some point in the life of a well cared for engine that will get its full potential life expectancy, that starter will need repair. Because of dis-assembly/assembly time it will cost you at the repair shop 2-3 times as much as the simple removal of a starter on a full crank. For DIY'ers many will find they are over their head repairing a starter on a half crank. Often owners will decide repair cost of these half cranks starters renders them disposable.

This isn't to say half crank units don't have their place. I used an IDC brand [Ryan/Riobi] line trimmer at home for many years with excellent service. But I knew how to fix it myself so there was no fear.

[wristpin]

Don't disagree with any of the above regarding torque etc and echo the pia factor of front mounted starters but while it doesn't suit the makers of budget hand held equipment it is possible to have an "external" starter with a single crank engine - Victa (Australian) did it with their Power Torque vertical crank engines on rotary mowers. The crank was supported on two large well spaced bearings and a conventional recoil starter mounted on top. Nothing flimsy about their kit which, in its day, was popular with both commercial and domestic users.

[hillsider]

Don't disagree with any of the above regarding torque etc and echo the pia factor of front mounted starters but while it doesn't suit the makers of budget hand held equipment it is possible to have an "external" starter with a single crank engine - Victa (Australian) did it with their Power Torque vertical crank engines on rotary mowers. The crank was supported on two large well spaced bearings and a conventional recoil starter mounted on top. Nothing flimsy about their kit which, in its day, was popular with both commercial and domestic users.

Strong yes but not indestructible! Saw one that for reasons best known to itself seized the big end bearing to the crank pin. The engine was powerful enough to drive through this until it unscrewed the crankpin from the web of the crankshaft which in turn destroyed the top half of the crankcase.