50cc to 70cc question


New Member
Hey, decided to upgrade the 50 to a 70 using the ooracing kit....the 50 is just too slow to accelerate safely.

Got the engine out, but all the tutorials I can find on youtube are for the GY6 engine which is a little different. There's a access hatch for the cam timing, as below. My question is, is the timing 'dot' on the sprocket supposed to point to the vertical notch?

Also, anyone know the easiest way to remove the sprocket, as it needs transferring to the new head.

Apologies for the incorrect terminology - it's the first time I've done this!

IMG_6646 by sagalout, on Flickr

Also does anyone know what the valve clearances should be as I guess I'll need to adjust these, or will they be set by ooracing as the whole head is complete?

Next question....the kit comes with a CDI, again with no instructions at all. I can't even see where this should plug in?


New Member
OK, managed to remove that, and now trying to install the new piston.....is there a technique for the circlips?! Been trying for 30 mins and can't even get the first one in, off the engine! Just doesn't seem close to fitting compared to the youtube videos I've seen?

stroker crazy

crazy as a fox
sagalout said:
… is there a technique for the circlips?!
If we're talking the little items that retain the gudgeon pin, they should just push into place with a bit of judicious help from a screwdriver.

If they're taking more than 30 seconds each something is definitely amiss!



New Member
Going to have another go later - was trying to prise it in with needle pliers but will try screwdriver.

Another question, what oil would you recommend? 10W40?


New Member
If it's cold where you are, try 10w-30. Valvoline should be readily available.

The clip is really easy, just for the love of mothers priceless shekels, place a rag around the conrod to prevent it dropping in.

Place one sharp end of the clip into the channel. Slide the other clip end towards the hole and it will compress and slip in. Takes 5 seconds and I usually just use my finger nail.


New Member
It's never that cold really - very rarely below zero!

These clips are really really stiff - I can't even bend enough to get one side in! Had another go this morning and only succeeded in cutting my finger open lol
According to my research - ;)

Put one of the circlips in place already then slip the gudgeon pin in so you only have to do one side. As for youtube vids, I have found one that helped me out when I did mine.

Its a 4 part so you can skip to the 4th.


The Ace 50cc motor is based on the old Honda ST50 motor.


New Member
Thanks, managed to get circlips on finally and now have engine rebuilt :)

Today's task getting it back in the bike!


New Member
HHmm, spoke too soon. Something isn't right :(

When I turn over the engine (on the bench) its very very stiff when the piston is at the top of the stroke. The spark plug is out so there should be little or no compression. I can only turn it over using a wrench on the crankshaft.

I thought when fitting it that the piston seemed to be hitting the head gasket, but assumed when it was all torqued down it 'was supposed to be like that'.

Any ideas what could be wrong before I strip it all down again :(

Pretty sure the seating pins were put back correctly (surely if they were wrong it would be a problem the other way anyway?)


New Member
OK, stripped it back down and there's good news and bad news!

Good news is I haven't broken anything, or installed anything 'wrong'.

Bad news is ooracing sent the wrong head gasket with the kit. When I took it back if and laid it out with the old one its exactly the same size :(

So now I'm stuck until tuesday, when hopefully I'll receive the proper one.

IMG_6653 by sagalout, on Flickr
I don't know what the actual compression is with that gasket but CRAZY did it without to up compression.He used silicone rtv instead. Perhaps it's possible to use that instead? Speak to your mechanic and see if it's safe to up compression.

That is if you don't want to wait....

Edit: Incorrect info as per corrections below. Ignore the above. No other choice but to wait for replacement...

stroker crazy

crazy as a fox
As 'orrible said, it was the base gasket I deleted. Silicon wouldn't last five minutes on the head and clearance between the valve and head might be problematic.

I am installing a 70 cc kit and whilst removing the head or barrel a positioning dowel fell out and not sure where it came from . Most dowels are straight tube , this one is " belled " one end , can anyone tell me what is its purpose .

Also at the front right hand head gasket area around the stud has a bigger hole with silicon ring all around it ,as this is the oil gallery is there a need for an oring as one came out ,but a new one is not supplied .

OK , Had a response from OO Racing , the dowel is an oil control dowel and its purpose is to stop the o ring going up into the gallery . Fit the dowel with the bell up is what he has recomended . These components i believe are not shown on the skyteam parts site engine diagrams .
Ok ,kit fitted ,as people have said , a different bike , after a quick ride i will take off the front tappet cover and run it to make sure i am getting oil up to the top ,this will be shown by the cams throwing oil out .You can remove the rear one and run it without any splash
One thing ,before putting the barrel in place reset "back/out " the chain adjuster and fit to the barrel with the 2 mounting bolts but without the central spring and its bolt . This spring will be put inplace once the cam sprocket has been mounted . I left this out and had to remove the starter to fit the adjuster assembly .


Nice work Paul. Glad bike is an improvement. Hopefully running bike in a dyno shootout on Saturday in Hackman

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Peter, if we look at the dlra 100cc record its 54 mph which is around 90 klm . Early days but it maybe achievable .If we feel confident we may have to share the entry and you take the record . Woo Hoo .
For yours and others info google target 550 as it will be in adelaide for 2 years for running at Lake Gairdner .
Our twin engine triumph build has stalled a little but is not forgotten .


That was the other suus bike. It is a doable record. Or even try m-f record. You have a year almost to prep bike. Shame there are no more spots left in the dyno comp this weekend. Would have been rewarding to see what your bike would pull

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In road trim today , 51 mph . 30cc under the 100cc is telling as you need to be right up with displacement , and 3 or 4 mph short of the 100cc record . . Will look at the tune up now and keep trying .
Recently i added to my helmet " bell style striping " , that obviously didn't work . Paul .

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