Predator Engine block cracked!!!! Suggestions

#1
Hi guys,
Been riding our minibike WAY too much! lol

SPent the last month fiddling with a Mikuni carb and finally had it dialed in. We have a fairly moderate built Predator engine on an Azusa minibike. Oil has been changed regularly. Current build is as follows for backgroun info

Predator 212
Arc Standard length rod with stock dished piston
Arc billeted flywheel
NR Racing 18cc head, milled 0.050, ported and polished with SS valves
26 lb springs, 1.3 ratio rockers on intake
Mod 2 Cam
Mikuni 22mm carb
Header (braced on block)
GTC TAV

Was riding today, hit probably 6500 rpms (usually no issue)....felt a surge and a "bang/Crack"...started throwing oil everywhere.
"Oh CRAP"...no power....manually shut it down immediately...walk home lol

My initial thought is that I threw a rod, as I could see a huge crack at top of engine (top of cylinder housing). I spent the next two hours stripping the engine and removing from frame. Interestingly enough, pretty much EVERYTHING is intact EXCEPT the block. The cylinder head literally broke off from the "crank case". Head is totally intact. I can post pictures if you think helpful. I had just checked oil prior to this ride.

A fractured block alone....is this a common failure? I realize this is a Chinese made block of variable quality. I ordered another block from EBAY.

In the mean time, I thought I would ask to see if there are any suggestion on avoiding a repeat of this?

Thanks
 
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#2
Someone else a while back had a similar issue and the consensus was that he left in the governor arm after removing the governor. It was free to move around and probably hit the crank. The crack originated right in front of the governor hole towards the head and cracked around most of the cylinder don't remember if the cyl came completely off or not. Show a pic of where it cracked.
 
#3
Someone else a while back had a similar issue and the consensus was that he left in the governor arm after removing the governor. It was free to move around and probably hit the crank. The crack originated right in front of the governor hole towards the head and cracked around most of the cylinder don't remember if the cyl came completely off or not. Show a pic of where it cracked.
Thanks Ole.

There was positively no governer arm left in engine. I had it open and cleaned it out during oil changes several times. I am wondering if there was some sort of harmonic effect in a bad block?
 

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trinik7597

Active Member
#5
nope you just poped the jug !!! it happens ... crap castings ... just buy another block on ebay or $100 dollar motor and throw your stuff at it and keep going :thumbsup:
 
#8
As everyone said it will happen to these when modified, just a matter of when it will . The more there modified the quicker they will go . Personally I would be proud of having that happen , you are making power .:thumbsup::thumbsup:
 
#9
Thanks you guys!

I have another quick question.

For simplicity sake, I will keep the stock dished piston to use in the new block. With the NEW BLOCK...should I get new rings? Or will they seat correctly in new block?
 
#10
if they are not damaged they will seat ... try to find a block that has rtc-1 on the casting . flywheel side of the block lower right hand corner
 
#11
My opinion the predator has an even shorter rod than the Honda and has higher side loads.
Can't prove it, but I think its a factor...
Thin castings.
Increased power since the old days.
Larger bore means less metal for structural support.

No top plate and support added.

I used to have pictures of some simple supports I made.
They are still here posted someplace, but I can not find them because the OldMiniBikes has moved them and locked them. ( without my permission they seem to feel they are the owner of my intellectual property ).
So search and if you stumble on my stuff feel free to re post it and ask what I did to reduce the block flex and failure risk.
 
#13
1.531 vs 1.556 on the R/S ratio, Predator to GX200, neither is great but I don't see massive wear on the thrust side of the bore/piston.

Pulling Kohlers tend to lift their tops too, so maybe NOSs girdle idea like the flatties run is an idea that's due? I've seen Charles' weld-up, but labor intensive and not so pretty:no: . A fairly simple plate on the flywheel side would beef that up, and one that bolts to the PTO bolts would tie crank and top tight.

Too much effort/expense, and the billet Animal block starts looking better.

Blocksupports
 
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#14
1.531 vs 1.556 on the R/S ratio, Predator to GX200, neither is great but I don't see massive wear on the thrust side of the bore/piston.

Pulling Kohlers tend to lift their tops too, so maybe NOSs girdle idea like the flatties run is an idea that's due? I've seen Charles' weld-up, but labor intensive and not so pretty:no: . A fairly simple plate on the flywheel side would beef that up, and one that bolts to the PTO bolts would tie crank and top tight.

Too much effort/expense, and the billet Animal block starts looking better.

Blocksupports
Interesting.....would that fit a predator?
 
#19
This is harder to explain than do, wish I could find my photos

I have no idea where the OldMiniBikes has put my intellectual property.
So good luck.....

Truth be told if I had my way I would delete every picture I ever posted here now.

Get some aluminum plate and start pounding.
Anyplace you can make a brace simple add a brace, this is not rocket science.
 
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#20
Something bothered me about this and I could not think of why....

I kept coming back to think about it.

Of course!
Nope lost it again....

Bugger...

You know what it was?
Loose bolts.

Chum nothing cracks up a block like loose bolts in the case cover.
They back out because the Chinese steel is soft.

Use hard bolts and or studs.
And this point is important the washer and lock washers you use are part of a system.
They must all be the same grade (8.8 ) or they will loosen again.

A dab of loctite ( blue ) also does not hurt.
 
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