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Mega ZX12 Rod.

Mega ZX12 Rod.

Old 04-05-2007, 12:07 AM
  #16  
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By the looks of that crank, the engine has a lot of mileage on it.

Have you by any chance measured the the crank pin?

Usually when a rod fails like yours, there will be some damage to the crank pin as well and on the pic it lookslike it got grooves in it.

Also, when an engine has high mileage, the crank pin goes oval (measure vertical and horizontal) and then the new rod will have slop in no time.

Here is one advise you should think about:

NEVER BUY A USED ENGINE

There is always a reason why engines are sold, and most of the time it's that they areworn out.

Just my 2 cents
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Old 04-05-2007, 12:29 AM
  #17  
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save your money and buy a new motor rather then rebuild it.

bang for your buck was good value if your on a budget, i must of put 20+ litres through mine (16% nitro) before it popped the origional rod, sad thing is i was going to put a rod into it before that race meeting but i couldnt get one .

i put a new p/l and rod in mine then about 5 litres of fuel later the bearings were cactas, i wasnt as happy with the performance of the new liner because the exhaust port was .5mm lower and the motor didnt perform the same.

your crank doesnt look that great...

how much run time has the engine done?
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Old 04-05-2007, 12:47 AM
  #18  
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Oh cr*p, looks like i've got a bad un then? huh, not too happy...i'm not sure about the mileage/hours on this engine, all i know is that he said the rod was replace 20 mins race ago, which i'm lead to beleive is a bit of a fib, as the brass bushing has come away from the rod....anyway, i've already installed the new rod, and seems to fit the crank pin well, quite snug...i'm just going to have to run this for a while till it blows, then not bother spending any money on it and buy a new engine.....i'll take it apart again after some running, and see if like you said happens, stefan, the new rod having slop in, we'll see....spend 45 on it so not throwing it yet.

If this has a lot of milage on it, does that explain the easy of the crank coming out? or am i missing an o-ring in that groove?
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Old 04-05-2007, 02:45 AM
  #19  
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Originally Posted by supermoto552
If this has a lot of milage on it, does that explain the easy of the crank coming out? or am i missing an o-ring in that groove?
That not a groove for an O-ring, but as you said earlier, for lubrication purposes, of the front bearing I think, never ever really thought about it....
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Old 04-05-2007, 03:23 AM
  #20  
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Originally Posted by supermoto552
Oh cr*p, looks like i've got a bad un then? huh, not too happy...i'm not sure about the mileage/hours on this engine, all i know is that he said the rod was replace 20 mins race ago, which i'm lead to beleive is a bit of a fib, as the brass bushing has come away from the rod....anyway, i've already installed the new rod, and seems to fit the crank pin well, quite snug...i'm just going to have to run this for a while till it blows, then not bother spending any money on it and buy a new engine.....i'll take it apart again after some running, and see if like you said happens, stefan, the new rod having slop in, we'll see....spend 45 on it so not throwing it yet.

If this has a lot of milage on it, does that explain the easy of the crank coming out? or am i missing an o-ring in that groove?
Nah, the crank usually comes out pretty easy and the groove is to keep oil at the front bearing.

You should always measure your crank pin with a caliper when you have your engine apart. If the pin is out of round by more than 3/10 th of a mm, don't bother with a new rod, it will be worn out after a liter or two.
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Old 04-05-2007, 12:22 PM
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Originally Posted by stefan
Nah, the crank usually comes out pretty easy and the groove is to keep oil at the front bearing.

You should always measure your crank pin with a caliper when you have your engine apart. If the pin is out of round by more than 3/10 th of a mm, don't bother with a new rod, it will be worn out after a liter or two.

Ah, thats good news about the crank i guess, meaning, the groove that it...not sure about the pin though, i'll measure it when i've run it for a couple of tanks, just wanna get it in the car i see if it actually work well as is, then i'll strip it down again and measure the crank pin roundness like you said.

If it is ovaled, do you reckon its worth throwing it, or actually buying a new crank, as its like 50! stands me at 70gpb so far 50 engine, 20 rod, guess i've learnt a lesson not to buy second had now i guess!!

Cheers for eveyones help and input by the way!
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