My grandson (age 9) is building the racing car.

He's nearly finished and is distraught that he has just noticed that when turning one rear wheel assembly (no wheels on yet) that each turns in opposite directions. I've been helping him by checking each step.

Do we have to go right back and any ideas which page he has done wrong?

Sorry I'm not a lego builder nor technical.

Thanks

Don't worry ;-)

Finish the build, put on wheels and see what happens. Everything will be fine!

Your car sure has the same problem, it is normal in all the cars around the world.

Oh great. Thanks. I adore my grandson but he does have a tendency to panic!

Why don't we all go round in circles then? My dad would be ashamed of me. He was a shipwright and seemingly knew how everything worked!

My husband was pretty good too but, very sadly, he died in November aged 71. My grandson's father left and remarried so is as much use as the proverbial! We may live in a liberated world but still feel the need for a man!!!

google differentials and how they work....

google differentials and how they work....

The short explanation is that a differential (in the Lego model this is a dark gray tubular part that has 3 small gears in it, located between the rear wheels) allows the wheels to rotate at different speeds. If the vehicle is stationary, then yes, one wheel will go forward and the other backward. If the vehicle is moving forward, then both wheels roll forward - but they may do so at different speeds. The reason for this is that when the car turns, one side of the car moves in a tighter curve than the other, so the wheels on that side move more slowly.

For a longer but very clear explanation, watch

.

This 1930s film explains it best:

Edited January 27, 201411 yr by nicjasno

That video breaks it down "barney style". If you can't understand differentials after that video, then I don't know what will teach the concept.

v/r

Andy

Thank you very much. The explanations and video have been very helpful.

Completed car does not move forward though. There doesn't seem to be the drive shaft or something is in too tight.. Hard to see now it's completed!

In other words the "Crown wheel" is not turning and there doesn't seem to be anything to make it turn.

I've always wanted a Morgan or a Caterham and now I feel I'm well on the way to a self-build!!

Pictures would be very helpfull, so we could pinpoint the problem.

By not moving forward, do you mean that it will not move easily when you push it due to some mechanical resistance? Pictures would be very helpful.

Welcome to the forum! Several things I would check:

1) Make sure the CVs are connected into each of the rear wheel hubs and differential. See instruction manual page 64

2) On instruction manual page 53, steps 1 and 2, make sure the tan axle with stud is placed correctly. If this part is inserted backwards (from the inside of the grey frame), the stud part may contact the differential and keep it form turning.

3) Check to see if the axles going into the engine block are in all the way. If they back out and one end of the crankshaft is not supported, the pistons can bind and make it harder to move. Check the grey axle on instruction manual page 69, and the red axle (not the red pin) on page 70, step 6. (I doubt this is a cause, but could be a possibility--check the other two first)

That's all I can think of. My guess is a CV or axle came out during assembly.

Edited January 27, 201411 yr by dhc6twinotter

We are homing in on the problem! The engine pistons are not moving as they should. One half are but on the other side two pistons are permanently down and the other two up. It would be useful if Lego instructions made a note to check the movement of moving parts before they become embedded and difficult to access later on.

The crown wheel is correctly linked.

Sorry guys I hadn't seen your helpful posts when I posted again. I'll make sure we check. Bedtime looms though!!!

yes rear wheels only turn together for a short distance before meeting resistance.

You are all awesome helping a granny in this way!

Seems like pistons are not installed correctly into the engine blocks? Are they sideways stuck?

if some pistons not moveing then they are stuck and causing the problem

try taking engine out and see if the crown wheel moves ok then

then you have isolated the issue and can rebuilt that part

Is it possible to lift out the engine without going right back to where it was fitted originally?

Thanks for that video. It didn't teach me anything new but it would have done a nice job at it.

Great video, thanks for posting

Yes I agree the video was good