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Engine basics => Engine set up tips => Topic started by: Tom Dugan on March 05, 2006, 12:35:25 PM

Title: Block Crack
Post by: Tom Dugan on March 05, 2006, 12:35:25 PM

Looking for your advise on repairing these small cracks.  Have thought about J&B Weld but not sure it would bond into the crack very well.  Is Alumiweld a possibility? Or, is this a problem at all?

The engine is a ST 46 that is in otherwise great condition.  Is this a common problem?  As always, your advice is welcomed.

I failed to mention that both side are cracke in the same place.

Thanks...Thomas

Title: Re: Block Crack
Post by: Bill Little on March 05, 2006, 12:51:06 PM

Hi Thomas,

I have made similar repairs with standard (not the quick set) J B Weld.  They have held up fine.  As you know, getting the area clean is of utmost importance.

That is a rather low stress point area, so sealing the crack is about all that would be needed.

Did you get my last email?  Phone number?

Thanks!

Title: Re: Block Crack
Post by: madhitter on March 05, 2006, 04:40:52 PM

I agree regular JB Weld is the way to go.  I was afraid to use it for a long time. but is great stuff for many of our needs.  (Older is wiser I guess)

Steve B

Edit:     The absolutely clean part is very important.  SB

Title: Re: Block Crack
Post by: Bill Little on March 05, 2006, 07:30:52 PM

Thomas,
One thing I remembered is to heat the JB Weld with a heat gun so that it thins a *little* bit and will be easier to force into the crack.  Sealing the area is all that will be needed.  If you put the spray bar in place, covered with melted vaseline, the hole will not get any in there and the spray bar will not stick in place.

Title: Re: Block Crack
Post by: RC Storick on May 17, 2006, 06:32:26 AM

This is not what some people like to hear but. I have always felt that when things like stress cracks happen it is best to replace the part. Buy the best the first time it will save you money in the long run.

Title: Re: Block Crack
Post by: RandySmith on May 17, 2006, 09:47:13 AM

Thomas 

 JB Weld  is  NOT  going  to  fix the  case, it  will break again or the epoxy will get soft and come loose, depends on where the  crack is.
Where is the case  cracked at?
The only REAL way is to have someone  weld this crack shut.  Using epoxy is  just a  temporary  fix

Randy

Title: Re: Block Crack
Post by: Bill Little on May 17, 2006, 10:05:43 AM

Hi Randy,

The cracks are where the NVA or keeper for the R/C carb goes.  At the top of the holes on the intake  throat.   You know, where a lot of guys fill with epoxy when they drop the sprinkler system and put the NVA through the case.

Bill <><

Title: Re: Block Crack
Post by: RandySmith on May 17, 2006, 11:34:41 AM

The cracked case  at  that point, where  the carb  mounts  is  almost  always  broken  because of a  crash.
I have seen this  about a hundred  times or  more in engines.  many times the crash will also warp the front of the case.

I have tried many times to repair this crack , but so far the only thing permanent has been  to weld it

Randy

Title: Re: Block Crack
Post by: Tom Dugan on May 17, 2006, 08:51:26 PM

Thanks All for the more recent advice.  Since my original post, I sent the engine to Frank Bowman to be checked and rebuilt.  Since the cracks are not actually in the round well that the venturi slides into but are in the flat spot where the venturi slide bolt goes, Frank recommends mounting the venturi normally and sealing with silicone.  I'm comfortable with doing that. 

Since I have several other ST46s I will have the venturi portion of the block milled down and the spray bar hole drilled trough.  I believe Tom Lay  and others do this also.   

This is still a good engine with many flights left on it.  If there is a simple fix then it seems a waste to relegate it to the parts bin and it won't be