Need To Help Four Stroke Combustion Engine on 3D model

The only big part that is geared to go round much faster than the crankshaft is the starter motor. They usually drive using gears rather than toothed belt as here, and I can see no particular advantage to this change to 'standard'. On the other hand, where is the device that disconnects the starter once the engine starts? Without it the starter will last for 30 seconds and then the armature will explode.

Sorry, doesn't make a lot of sense to me.

Cheers, Tim

At the risk of spoiling the fun ...

This might be £14.99 well-spent

**LINK**

http://www.agrimanuals.com/mercedes-benz-engine-om421-om422-om423-om424-om421a-om422a-om423a-om424a-om421la-operators-manual-11789-p.asp

MichaelG.

Tim in Jon's 3D model the starter is labelled item 20 with the starter solenoid as 19.

Muzzer and Michael, I think while there are some superficial similarities to the Merc power unit, from following the link that Neil found to the origin of the model and looking at some of the internal details I'd be very surprised if Mercedes had any input to the model at all. As I said earlier - a 24 valve engine with only 12 push-rods, and each of those operating 2 valves by pushing on a bridge piece attached to the stem each of the valves. That would put an appreciable side load on the valve stems, which in turn would give quicker guide/stem wear, so considering that Mercs are known for reliability it would seem a very odd design decision.

The cylindrical item the OP asked about is not only belt driven but the crank pulley seems to be spaced off from the crank by a vibration damper or similar, so another level of disconnect to what appears to be some sort of oil pump - surely not a satisfactory solution for a real engine as opposed to a design concept.

On 2nd thoughts, I'd like to change my vote to Air-Con Compressor!

Where is that man who used to run a lorry garage?

Second thoughts its the weekend and maybe better off not knowing what he is upto

The mind boggles

Hi, thanks for the replies.

Keith, a setup as shown in the model is not wholly unusual for a 24 valve engine with 12 push rods, typically it is employed for slower speed engines. An image shows this below:

http://www.tpub.com/engine3/en3_files/image088.jpg

From responses on other forums, the part appears to be a scavenge dry sump oil pump. I will be checking this over the coming week though to confirm. The alternator could be mounted on the same shaft, or be oil cooled, again, need to check.

http://www.enginebuildermag.com/wp-content/uploads/Articles/12_31_2007/38721drysumpgif_00000012655.gif

It seems impossible to say without reference to the manufacturer's literature. It does not fit the normal description for a fuel pump, oil pump, air con compressor, alternator, starter motor, air injection pump, hydraulic PTO pump or brake vacuum pump. It is odd because is it very large in scale to the rest of the engine and is geared to run very fast.

The location and the shallowness of the sump would tend toward a dry sump oil pump but it seems huge for that task and a bit lacking in plumbing. If you can find out what kind of engine it is and google the oil pump image you might get lucky.

As it is a drawn engine and not a photograph, though, it is possibly a figment of the drawer's imagination, is it not?

Edited By Hopper on 11/02/2017 23:42:07

Edited By Hopper on 11/02/2017 23:50:40

If its a truck motor, could it be a hydraulic pump. At first I thought of a hydraulic motor for starting, but that wouldn't work, you need the motor started to get hydraulic pressure. If it is it seems a bit high geared.

Ian S C