Inner rotor kit in a '79 z50r

3401 Views 18 Replies 8 Participants Last post by dirtbkr188, Jan 22, 2010

ryan's dad

Discussion Starter · Dec 22, 2008

What would I need to do to make an inner rotor ignition kit work in my stock '79 Z50R? I'm really intrigued with the concept. Have any of you tried one? thanks for the time Dennis

1 - 19 of 19 Posts

thorwarrior915

· #2 · Dec 22, 2008

did it with an early 80's. here we go...

The taper for the flywheel (where the keway is) is different between 6V motors and 12V motors. Your 79 model is a 6V points ignition motor. To my knowledge, IRK's for the 6V cranks are not readily available... however one of the hardcore tuning companies from overseas may make something. I went the ebay route. Here is what you will need to do

Method 1:

-Browse ebay for a crank adapter that will change the taper of the crank from the 6V style to the 12V style. They are out there.

-Pick up an inner rotor. I would suggest grabbing one from Mark at AHP minis... thats where I got mine and it hasn't skipped a beat, plus its simple to install. Dont forget a new 12V coil!

-Get a flywheel puller too (grab it from mark when you order the IRK)

-Pull your stock flywheel and stator plate off. Make sure to use an impact driver on the #3 phillips head screws on the stator or they will strip out. Also, dont lose the little O-rings that go behind the screws on the stator plate... dont remember if it came with new ones or not. Install the new IRK stator plate and rotor (little flywheel) with the crank adapter in place. Mount your IRK cdi box, and new 12V coil that you bought seperately. Wire it up and rev away.

Method 2:

-Buy an OEM XR/CRF50 crank from honda, or out of the classifieds here... or an aftermarket stock style crank from DRatv.com. Because of the year of your motor, you will need an XR/CRF50 piston kit, and head to get the right deck height/dome/compression ratio. Sounds scary, but you can pick up somebody's stock engine parts for dirt cheap after they do a race head big bore kit install.

-Get yourself a complete gasket kit while you are at it.

-Split the cases and swap cranks, then put it all back together with new gaskets and top end.

-Any inner rotor will simply bolt on to the crank now with no adapter, and your motor will be completely fresh and worthy of performance goodies. Not to mention you got rid of the junk points!

I opted for choice A because I was feeling cheap... but its up to you.

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firepower354

· #3 · Dec 22, 2008

Need an 82-87 piston for a 12v crank swap, won't he?

thorwarrior915

· #4 · Dec 22, 2008

3

I'm not really experienced in making different year pistons make with different domes, but I know if you replace it all with XR/CRF parts like I said above it will work, and replacement parts will always be easy to find. Long rod, short rod... big dome... no dome. Too many variants.

Edit... so I'm bored...

69-81 piston looks like this

82-87 piston looks like this

and the last generation piston

So firepower... the way I see it, If he ran an 82-87 piston with his 79 head and an XR/CRF crank... it would be super low on compression because the old heads had some super dome going on? Maybe I'm misinterpreting what you said...

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OLDSCHOOL

· #5 · Dec 22, 2008

my opinion and experiance.. (I run a IRK in my stocker)

Since its going to cost you way to much money to convert over and you will not see any Preformance gain (2-stroke rev effect) or quick throttle responce.

Have your Flywheel proffesionaly Lightend as much material as can possibly be removed...and keep it safe ( up to -10oz) of material removed ($45.00 and $60.00)

you will get close to the same effect that the IRK is going to give you without losing any momentum in the corners

See less See more

ryan's dad

Discussion Starter · #6 · Dec 23, 2008

thorwarrior915 said:
did it with an early 80's. here we go...

The taper for the flywheel (where the keway is) is different between 6V motors and 12V motors. Your 79 model is a 6V points ignition motor. To my knowledge, IRK's for the 6V cranks are not readily available... however one of the hardcore tuning companies from overseas may make something. I went the ebay route. Here is what you will need to do

Method 1:

-Browse ebay for a crank adapter that will change the taper of the crank from the 6V style to the 12V style. They are out there.

-Pick up an inner rotor. I would suggest grabbing one from Mark at AHP minis... thats where I got mine and it hasn't skipped a beat, plus its simple to install. Dont forget a new 12V coil!

-Get a flywheel puller too (grab it from mark when you order the IRK)

-Pull your stock flywheel and stator plate off. Make sure to use an impact driver on the #3 phillips head screws on the stator or they will strip out. Also, dont lose the little O-rings that go behind the screws on the stator plate... dont remember if it came with new ones or not. Install the new IRK stator plate and rotor (little flywheel) with the crank adapter in place. Mount your IRK cdi box, and new 12V coil that you bought seperately. Wire it up and rev away.

Method 2:

-Buy an OEM XR/CRF50 crank from honda, or out of the classifieds here... or an aftermarket stock style crank from DRatv.com. Because of the year of your motor, you will need an XR/CRF50 piston kit, and head to get the right deck height/dome/compression ratio. Sounds scary, but you can pick up somebody's stock engine parts for dirt cheap after they do a race head big bore kit install.

-Get yourself a complete gasket kit while you are at it.

-Split the cases and swap cranks, then put it all back together with new gaskets and top end.

-Any inner rotor will simply bolt on to the crank now with no adapter, and your motor will be completely fresh and worthy of performance goodies. Not to mention you got rid of the junk points!

I opted for choice A because I was feeling cheap... but its up to you.

thanks for all the info. Are you happy with the IRK? Are there any cons to it? I like the sound of option "A" also. Thanks alot Dennis

firepower354

· #7 · Dec 23, 2008

thorwarrior915 said:
So firepower... the way I see it, If he ran an 82-87 piston with his 79 head and an XR/CRF crank... it would be super low on compression because the old heads had some super dome going on? Maybe I'm misinterpreting what you said...

Likely, but an early piston will stick 3mm out of the top of the jug. Swapping a 6v rod on to the 12v crank is about $65

dirtbkr188

· #8 · Dec 23, 2008

firepower354 said:
Likely, but an early piston will stick 3mm out of the top of the jug. Swapping a 6v rod on to the 12v crank is about $65

An early piston, meaning '69 through '81, correct, Terry? The '82 and newer engines have the same long rod that the XR/CRF has, wouldn't the '82-'87 be compatible with the pre '81 head, or would there still be considerable compression loss?

firepower354

· #9 · Dec 23, 2008

I thought the 82-87 chamber was the same as the 81-back, but I dunno... ThongWarrior says no

thorwarrior915

· #10 · Dec 23, 2008

ryan's dad said:
thanks for all the info. Are you happy with the IRK? Are there any cons to it? I like the sound of option "A" also. Thanks alot Dennis

Glad I could help. Cons... well, I put the IRK on an 86 points motor with a stock head takegawa 88 kit. With the stock jetting on the stock carb, I couldn't get the bike to idle. Unfortunately with a stock 50 carb there is no way to play with the pilot jet unless maybe you can drill the passage out?

Long story short, I put a stock XR70 carb on it and got it to run stronger and idle at the same time. It is definately easy to stall, even with the auto clutch... but thats probably a tuning issue. I have never ridden an IRK on a stock bore so I can't help there. The bigger the displacement, the better I like an IRK. Makes a stock chinese 125 rev and sound like a 250F

thorwarrior915

· #11 · Dec 23, 2008

firepower354 said:
I thought the 82-87 chamber was the same as the 81-back, but I dunno... ThongWarrior says no

Sounds like somebody has their panties in a bunch.:lol: I double checked my thoughts on DRATV and they say 81 and back had the "old 50 dome"/short rod combo. 82-up has "new 50 dome".

By the way firepower WTF IS IN YOUR AVATAR???? I stare at it from time to time and cant figure out if its a pile of naked women, or some kind of abstract art... Like a barbie assembly line blew up and they melted into a pile of arms and heads???

dirtbkr188

· #12 · Dec 23, 2008

thorwarrior915 said:
...By the way firepower WTF IS IN YOUR AVATAR???? ...

He calls it an intervention...looks more like a group grope to me...

LoudFastUgly

· #13 · Dec 23, 2008

OLDSCHOOL said:
my opinion and experiance.. (I run a IRK in my stocker)

Since its going to cost you way to much money to convert over and you will not see any Preformance gain (2-stroke rev effect) or quick throttle responce.

Have your Flywheel proffesionaly Lightend as much material as can possibly be removed...and keep it safe ( up to -10oz) of material removed ($45.00 and $60.00)

you will get close to the same effect that the IRK is going to give you without losing any momentum in the corners

Wouldn't have any pics of a lightened flywheel wouldya?

Some measurements would be real nice too.

firepower354

· #14 · Dec 24, 2008

thorwarrior915 said:
Sounds like somebody has their panties in a bunch.:lol: I double checked my thoughts on DRATV and they say 81 and back had the "old 50 dome"/short rod combo. 82-up has "new 50 dome".

By the way firepower WTF IS IN YOUR AVATAR???? I stare at it from time to time and cant figure out if its a pile of naked women, or some kind of abstract art... Like a barbie assembly line blew up and they melted into a pile of arms and heads???

DrATV says the 82-up has a new dome, but the OE 82-87 piston has a dome that won't clear an XR/CRF head. Might be three different chambers, or the Dr is dipping in to the med cabinet???

It's just a pile of mannequin parts, sadly

Panties? Nah. I figure something born in the wild shouldn't be "raised" in captivity, ya see.

thorwarrior915

· #15 · Dec 24, 2008

I was suprisingly accurate with the blown up pile of barbies. I believe you are right about the 82-87 piston having more of a dome... because that is the one that people turn down to make a HC xr/crf piston on the cheap.

dax

· #16 · Dec 24, 2008

If using either 1 or 2 method, are you able to use original 6v points type flywheel cover?

How about if you installed an outer rotor kit using either method?

dirtbkr188

· #17 · Dec 24, 2008

You can use the original 6V ignition cover if you use the inner rotor kit on the stock crank. If you swap out to a 12V crank, it is approximately 3/8" wider on the left side, and the 6V ignition cover will not fit in place properly.

Depending on the inner rotor kit you use, you MIGHT be able to grind the extra 3/8" off the 12V crank end, and still use the 6V ignition cover.

mx2007

· #18 · Jan 22, 2010

hey were can i get a crank adapter? i cant find one

dirtbkr188

· #19 · Jan 22, 2010

mx2007 said:
hey were can i get a crank adapter? i cant find one

The adapter isn't made to be used on an XR70 crank...see HERE

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