rotostart to pullstart conversion

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alexwright

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30
hello all.
I am sorry if this has already been covered but I have looked through the forum to no avail.

I want to change from rotostart to pullstart
most places are selling the pull start I need but state "no one way bearing included"
do I need a one way bearing or did the rotostart already have one?
please see photo attached
please note this is the savage x 4.6 rtr latest version with the F4.6 engine and drill shape style rotostart
 

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You need a OWB. The hub with grub crew was placed as a rotostart unit but isn't a real one.

Be sure to check the starting shaft for damage.
I think the grub screw has damaged the shaft.

What engine is it?
 
thanks for your reply
it is the F4.6 engine
there are 2 grub screws that sit on 2 flat spots on the shaft so there is no damage
will the one way bearing replace the metal hub then?
 
The 2 flat spots on the shaft ARE the damage.
The shaft is supposed to be round..
So you need the shaft and a one way bearing.
 
Post a picture of the other end of the shaft where the flats are at.... I believe the one way is in the backplate assembly you have
 
thanks jam
this is doing my head in now haha
there are no bearings in this assembly
what is the purpose of the owb?
there is a small spring pin on the bottom of the con rod that sits in the Grove one he back if that shaft that prevents you from turning the engine the wrong way
 

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The owb on this assembly should be on the outside and in the pullstarter.
If the owb is on the inside the shaft has a hex on the outside. As used on the K4. 6.
 
That is the exact meaning of One Way Bearing. If you turn it clockwise it will turn the shaft and if turned counter clockwise it will spin freely like a bearing.
 
I think that shaft has machined flats on it, and i do think there is a one way bearing in that backplate.. other wise how would it start the engine as you outlined earlier... post a pic of the other side of that backplate for me to :eyes:
 
I am sure there is no owb on the inside. The flat spots on the shaft ARE done very well but not by the engine manufacturer.

Stock F4.6 OWB is on the outside of the backplate.
 
hpi-savage-x-f4-6-nitro-start-backplate-one-way-shaft-109535-4-6-roto-screws-c3d9e7801ad13158dc47b6ecc6ac868b.jpg

I believe this is the setup (Nitro Start). I have the same on one of my Savages and it uses a "special" starter that turns in the direction that the motor turns so is a direct drive similar to a pull start action. The OWB will not grip the shaft with the flats on so you are better off replacing the back plate with one that is compatible with the pull start.
 
the back plate has no bearing in it
the shaft goes through the hole very snug and will spin in bother directions no problem
when it is all built together you can turn the starter shaft in both directions
clockwise the engine will turn
counter clockwise the engine will not turn but you can still rotate the shaft. every 360 degrees you hear the small spring pin on the bottom of the con rod drop back into that groove
 

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It was standard on some of the F4.6 engines and I am assuming it was something that HPI came up with to remove the need for a OWB and allow people to use a standard drill to start the engine. It is a pain though when you have 1 on Nitro Start and 1 on Roto Start as you need 2 different starters!!! My engine is over 2 years old and it was standard on it so am assuming it has been around for a while.
 
so if the OWB is in the rotostart itself I will need a OWB and a pullstart then
will the OWB fit onto this shaft ok if it has 2 flat spots?
I can't see how a bearing can grip the shaft enough to turn the engine over!
 
No, you will need to replace the backplate and shaft with one that will take a OWB (similar to below but make sure you get the correct one for your engine). As you can see, the shaft is perfectly round for the OWB to grip. You will, of course, need to get a OWB as well and once again make sure you get the right size.

upload_2016-2-28_19-51-55.jpeg
 
firstly that's everybody for your input
please see image attached that explains all!
I found this on HPI website you can
buy the engine I have on its own and it comes with a pullstart
I downloaded the user manual for the engine and this diagram answers all the questions
 
so sorry jam
I must have missed your post!
would have saved me a lot of time and stress if I hadn't of missed it haha! thanks again
 
Haha you could say good to go
will cost about £50 or $70 usd for me to get sll the parts here int he uk!
 

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