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» Welcome to Pocket Bike Racing

Poor Cag engine mounts (pic)

Posted in Pocket Bikes Performance Tips

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Old 07-03-2009, 10:16 AM
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Poor Cag engine mounts (pic)

While many of use have all heard about how the engine mounts on cags arnt exactly level but today I found out exactly how much. I did a bit of a milling on my crankcase in preparation for an engine build and I thought I woudl clean up the mounts. I clamped the case upside down, rested a shaft through the middle of the crank bearings and then put a digital angle gauge on it to confirm it was clamped level. I can happily say the front and back face of the cags are within 0.3 degrees of being 90 degrees of the central line of the crank which is a nice change from the rest.

However when I got to the mounts it was sad indeed, starting with the lowest mount I took the minimum amount of material off it and then took the same off the rest. In the end I found one of the front corner mounts was the lowest and it was 1.4mm different in height than the rear 3!

Here is a pic:

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Old 08-03-2009, 03:37 AM
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gromet is an unknown quantity at this point
good work m8.. It makes you wonder if they can get that so wrong, Its amazing the engines even start with all the other stuff they would get wrong...
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Old 08-03-2009, 04:24 AM
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That's pretty impressively bad when you think about it. Goes to show why so many people have problems aliening sprockets and what not on their cags.
What's worse is that when it comes to Chinese made bikes the only thing that is consistent in them is that they are all inconsistent. Each bike is unique.
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Old 08-03-2009, 02:34 PM
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gromet: thanks, Luckily for me I have found that the main measurments are ok, as in the line of the two bearings is 90 degrees to the face of the clutch area and the pullstart face, this means I didnt have to make some jig to start machining this engine to blueprint it, I could immeadiately clamp it in the vice and do what I wanted. Sadly for the rest of its pretty sad as you say.

Crash Dummy: I tottaly agree, it looks like some of the machining work is fairly good but many of the things that involved casting are downright terrible. The problem with the mounts is that they very much look like they have been rough cast, drilled and tapped and then chucked on a linisher to make them somewhat even, too bad they are all evenly wrong. I also as you wonder how many people are having issues with things like chains always coming off because of crap like this. When I used to use a cag engine in my scooter I used to use packing washers to get the aligment right.
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Old 08-03-2009, 04:33 PM
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gromet is an unknown quantity at this point
I know how hard it is to find a cag back wheel that's inline....
So the sprocket bolts central to the wheel so the chain don't go loose then tight when u spin it...
Maybe you could do a review on this one day
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Old 08-03-2009, 06:15 PM
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I found my crank case was not too bad, around .030" out. I used a mandrel to allign mine, machined with steps to suit the bearing and seal housings.

Biggest problems with cags is the quality they have been built too. even for my stock crankshaft i had to drill out one half of the crank big end journal bores 1mm, press the big end journal into the other half, stick it in my crank alignment tool and weld the big end journal into the half i drilled out.

If you spend enough time machining and Q.A.ing all your parts the life expectancy and performance can be greatly increased.



Oh, and one thing to check, once you have machined your engine mounts level, make sure you check that the engine plate on the frame is flat and perpindicular to the back wheel. No good machinging your engine if your frame is wrong anyway.
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Old 08-03-2009, 06:35 PM
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gromet that can be organised if I think of a way to do it as I need to grab the wheel from the bearing mounts, I might need to machine something up for it. However I dont know how I could correct this problem unless I could use a front wheel and drill the other side out for the sprocket. My other idea is to machine the center of the sprocket out a little, machine the wheel to have a step in it and then elongate the holes, this way the sprocket sits on the step and uses that for a location instead of the bolts. That is assuming that its not the sprocket itself that is out of round. But I do have good reason to find thos out as I believe that I will be having this sprocket turning to one of the highest speeds in this whole forum, a big claim I know.
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Old 08-03-2009, 06:40 PM
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Quote:
Originally Posted by TheUFO View Post
I found my crank case was not too bad, around .030" out. I used a mandrel to allign mine, machined with steps to suit the bearing and seal housings.

Oh, and one thing to check, once you have machined your engine mounts level, make sure you check that the engine plate on the frame is flat and perpindicular to the back wheel. No good machinging your engine if your frame is wrong anyway.
UFOman I will ask you more about your machining and corrections in your tool thread which I must say I find very interesting.

As for the engine plate your very right, lucky for me I am not using any of my engines for bikes at all so I an all set
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Old 08-03-2009, 07:25 PM
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This is abit off topic but i snapped one of my engine mounts off by over tightening,
the middle one under where the clutch/sprocket is to be exact.

Is there any chance the other engine mounts will brake or weaken in coherence with the missing mount?
And is there anything i can do to resolve this?
or am i forced to run with the remaining 4mounts?

Helpful advice would be much appreciated.
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Old 08-03-2009, 07:59 PM
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With those three mounts being so close to each other I cant see it being an issue
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