Chain rings

[Bigbee]

We're working on a new central crank motor with a foreign factory.The first bike we didnt like as it was under powered,so they have developed a newer motor.Rather than ship a complete bike I said to ship the new motor only and we will fit it our selves.We've just taken off the old chain ring which is held on with four bolts.The new motor has fixing for five bolts,can I just replace the four bolt chain ring with a new five bolt chainring set?Why do some have 4 bolts and others 5? Sorry to sound so dumb!

 

[flecc]

If it can take either, by all means use whichever is convenient.

The variations are mainly due to needing strength when the chainring diameters are larger (more teeth), five spoke keeping spoke to spoke unsupported length of the ring outer within bounds.
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[Old Timer]

We're working on a new central crank motor with a foreign factory.The first bike we didnt like as it was under powered,so they have developed a newer motor.Rather than ship a complete bike I said to ship the new motor only and we will fit it our selves.We've just taken off the old chain ring which is held on with four bolts.The new motor has fixing for five bolts,can I just replace the four bolt chain ring with a new five bolt chainring set?Why do some have 4 bolts and others 5? Sorry to sound so dumb!

Also worth a mention is the different hole centres (BCD = bolt circle diameter) between the fixing bolts. See here Bicycle Chainrings (Chainwheels) from Harris Cyclery