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cracked piston - thoughts?
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iamdonquixote
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PostPosted: Sat Nov 19, 2016 4:43 pm    Post subject: cracked piston - thoughts? Reply with quote

Pulled the engine because it had quite a bit of blow by. See: http://www.thesamba.com/vw/forum/viewtopic.php?t=667243&highlight=

The spark plugs on the 3/4 side looked good but the 1/2 side looked black , so I started by pulling the 1/2 side head.

Well the #2 looked like this:
Image may have been reduced in size. Click image to view fullscreen.


I could see oil push through the crack as I turned the engine over.
thoughts? what could have caused this?
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modok
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PostPosted: Sat Nov 19, 2016 5:47 pm    Post subject: Re: cracked piston - thoughts? Reply with quote

It would be VERY RARE for a piston to crack like that.
Call it a casting defect, replace all four, don't worry about it happening again.
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iamdonquixote
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PostPosted: Sat Nov 19, 2016 5:53 pm    Post subject: Re: cracked piston - thoughts? Reply with quote

modok wrote:
It would be VERY RARE for a piston to crack like that.
Call it a casting defect, replace all four, don't worry about it happening again.

thanks, I never heard of it myself, I assume its the cause of the blow by?
Anything else to check out? Should I split the case?
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PostPosted: Sun Nov 20, 2016 8:21 pm    Post subject: Re: cracked piston - thoughts? Reply with quote

Some additional pictures of the head and #1 piston and cylinder.

Image may have been reduced in size. Click image to view fullscreen.


Image may have been reduced in size. Click image to view fullscreen.
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PostPosted: Sun Nov 20, 2016 8:26 pm    Post subject: Re: cracked piston - thoughts? Reply with quote

unless you have the spark plugs loose you have the wrong ones in those heads as far as the crack just replace all four and call it good
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PostPosted: Mon Nov 21, 2016 8:42 am    Post subject: Re: cracked piston - thoughts? Reply with quote

The crack is inline with the wrist pin. Could be caused by detonation due to some low octane gas or excessive compression ratio.
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PostPosted: Wed Nov 30, 2016 12:13 pm    Post subject: Re: cracked piston - thoughts? Reply with quote

The spark plugs are just loosely threaded in.

Took, the #3 piston & cylinder off.
Things look bad, thoughts on why this occured?
Image may have been reduced in size. Click image to view fullscreen.

Image may have been reduced in size. Click image to view fullscreen.

Image may have been reduced in size. Click image to view fullscreen.

Image may have been reduced in size. Click image to view fullscreen.
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PostPosted: Wed Nov 30, 2016 12:40 pm    Post subject: Re: cracked piston - thoughts? Reply with quote

Detonation/ Preignition
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PostPosted: Wed Nov 30, 2016 12:45 pm    Post subject: Re: cracked piston - thoughts? Reply with quote

Zundfolge1432 wrote:
Detonation/ Preignition
But I remember when auto manufacturers used to say that a little bit of that noise was normal. Very Happy
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PostPosted: Wed Nov 30, 2016 5:32 pm    Post subject: Re: cracked piston - thoughts? Reply with quote

Zundfolge1432 wrote:
Detonation/ Preignition


Yep. Pretty much confirms my earlier post.

The only other thing that could cause that much damage would be a sledge hammer.

By the way, you are taking a really big chance if you just put new rods and pistons and cylinders on that engine. All of that broken and squished out metal has surely contaminated the bearings and oil ways, probably scored the crank and oil pump and crudded up the oil cooler. The crank could be bent too. I would call the rods toast. I also wouldn't rule out case damage and cracks.


Time for a full tear down and rebuild. Bummer.

If the case was machined where the cylinders sit or the heads were re decked and then it was not shimmed to bring the compression ratio back down then the CR might have been very high and combined with bad gas you will get detonation. The distributor also could have been set wrong causing too much advance or retardation.
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Last edited by splitjunkie on Wed Nov 30, 2016 5:41 pm; edited 1 time in total
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PostPosted: Wed Nov 30, 2016 5:38 pm    Post subject: Re: cracked piston - thoughts? Reply with quote

splitjunkie wrote:
Zundfolge1432 wrote:
Detonation/ Preignition


Yep. Pretty much confirms my earlier post.

The only other thing that could cause that much damage would be a sledge hammer.

By the way, you are taking a really big chance if you just put new rods and pistons and cylinders on that engine. All of that broken and squished out metal has surely contaminated the bearings and oil ways, probably scored the crank and oil pump and crudded up the oil cooler. The crank could be bent too.

Time for a full tear down and rebuild. Bummer.


In fact you'll see marks on the rod bearings as well sometimes called aligatoring . Take pics.
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PostPosted: Wed Nov 30, 2016 6:11 pm    Post subject: Re: cracked piston - thoughts? Reply with quote

That also looks like a very tight pin to small end of the rod fit- with that damage to the end of the pin and pin bore in the piston.

Would that go along with detonation??? or looking at 2 problems?
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PostPosted: Wed Nov 30, 2016 6:21 pm    Post subject: Re: cracked piston - thoughts? Reply with quote

iamdonquixote wrote:
The spark plugs are just loosely threaded in.

Took, the #3 piston & cylinder off.
Things look bad, thoughts on why this occured?
Image may have been reduced in size. Click image to view fullscreen.


that could be caused by many things. You will have to guess based on the other clues you have. If the piston tried to seize or the pin tried to seize you should be able to see that on the skirt. If if the skirt is small (bent in) at the bottom then possibly the pin seized. If it overheated you will have four corner scoring. The pin may have seized and broke the piston, or the piston may have broke first, due to who knows why. Ring butted, hydrolocked on fuel? Detonation maybe but once cleaned you should see some sign of it.
Measuring the skirt and examining the piston, check ring gaps, and knowing the conditions is all you can do. Was the pin clips still in place? possibly the pin walked sideways and caused it. Many VW shops do not know "Rod alignment" is a thing.
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PostPosted: Sat Dec 03, 2016 7:56 am    Post subject: Re: cracked piston - thoughts? Reply with quote

Embarassed Embarassed so what did the rest of the pistons look like?

Show us her skirts Rolling Eyes
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Last edited by williamM on Sat Dec 03, 2016 4:23 pm; edited 1 time in total
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PostPosted: Sat Dec 03, 2016 3:23 pm    Post subject: Re: cracked piston - thoughts? Reply with quote

williamM wrote:
Embarassed Embarassed so what did the rest of the pistons look like?


I'm curious also!
The top of #2 . . .
iamdonquixote wrote:
Well the #2 looked like this:
Image may have been reduced in size. Click image to view fullscreen.



The bottom of #3 . . .
iamdonquixote wrote:

Took, the #3 piston & cylinder off.
Image may have been reduced in size. Click image to view fullscreen.


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PostPosted: Sun Mar 05, 2017 5:41 pm    Post subject: Re: #2 cracked piston - thoughts? Reply with quote

well , I spilt apart the case, and I'm in need of expert advice on its usability.
I'm concerned about the dowel pin that is loose at the rear bearing saddle.
Also, it appears that the installed the bearings incorrectly as the oiling hole in the bearing did not line up with the one in the case.
Image may have been reduced in size. Click image to view fullscreen.

Image may have been reduced in size. Click image to view fullscreen.


also, in my post I wrote it was the #3 cylinder but it was #2.
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PostPosted: Sun Mar 05, 2017 5:57 pm    Post subject: Re: cracked piston - thoughts? Reply with quote

How do those lifter brackets work- I'm unfamiliar with that set up.

judging by the groove in the #3 bearing, your due for an excessive line bore or a new block.
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Last edited by williamM on Sun Mar 05, 2017 6:00 pm; edited 1 time in total
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PostPosted: Sun Mar 05, 2017 5:59 pm    Post subject: Re: cracked piston - thoughts? Reply with quote

williamM wrote:
How do those lifter brackets work- I'm unfamiliar with that set up.

I thought that was a 36 hp thing? But I've never looked inside a 36 hp block until today.


Last edited by iamdonquixote on Sun Mar 05, 2017 8:46 pm; edited 1 time in total
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PostPosted: Sun Mar 05, 2017 7:19 pm    Post subject: Re: cracked piston - thoughts? Reply with quote

That is a 36hp case...which is why you see those lifter guides.

I highly recommend you take this to the Vintage Speed Forum. The 36hp experts hang out over there.

I will tell you, rebuilding 36hp engines cost much more than late models. Less parts available and some are expensive.

Mr. Okrasa is selling a few stroker 36hp based engines for I believe $3200.

For reference, I had to spend $900 in case machine work to get my 36hp case back to spec.
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PostPosted: Sun Mar 05, 2017 8:45 pm    Post subject: Re: cracked piston - thoughts? Reply with quote

calling admin,, can we move this thread to vintage speed forum?
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