Sign in to follow this  
Followers 0

Melted piston from overheat due to coolant loss- repair plan?

21 posts in this topic

Posted

I was out on the water doing the break-in procedure and taxi tests for my new 670, and during the 4500RPM step, I noticed a sudden loss of a few hundred RPM and a rapidly increasing and erratic coolant temp.  I idled the engine, and decided to taxi back to the boat launch, with coolant temps hovering about 180, but erratic.   I found the coolant level just below the water pump (engine is inverted), and I'm sure I was boiling coolant in the heads even though the CHT showed 180- that must have been the erratic part.   I haven't located the exact leak location yet, but there is coolant spray all over the pusher prop, tail and empannage.   

Anyway, the #1 piston's edge is melted at the exhaust port, and the cylinder crosshatching is gone at the 4 corners.    #2 cylinder looks fine, at least from the exhaust port view. 

So- my question:  Is it a reasonable repair plan to just rehone, install new pistons, and possibly new head if it's warped?

PS-  The overheat is certainly my fault and I'm really happy with Rotax Rick's 670.  I definitely have no complaint at this point about his product.   The few minutes I got to spend with it, it seems awesome and I can hardly wait.   Very smooth, and the boat clawed its way onto step at 4500RPM, which almost unbelievable.  6100RPM minimum needed with the 582.  

Share this post


Link to post
Share on other sites

Posted

If the cylinder is not scored to deep then you should be able to hone and put in a new piston.  Make sure you measure ring gap etc to make sure all is well in the jug.

I do all my break ins at the house with the plane tied down.  If it trys to get too hot either shut down and let it cool off then restart the break in where you left off, OR I use the garden hose with a fine mist spraying on the rads to keep the temps where I want them.  When I do it with the plane tied down I can stay outside the cockpit and keep an eye on the engine just to make sure all is OK during break in. 

If you have a good nozzle, you can put a VERY fine mist on the rads that dries almost immediately and wont be running back on the plane or prop.

Sorry you had a burn down on the break in.. My first 582 puked on me when I did not get the RV oil cavity fully bled and the brass gear melted down on me.  Lesson hard learned!  I watch fluid levels like a hawk now on rebuilds or new engines during break in.

:BC:

 

1 person likes this

Share this post


Link to post
Share on other sites

Posted (edited)

Man...  sorry to hear that happened.

From my experience in Rotax snowmo rebuilding I have found that when you melt a little aluminum like that it gets smeared into the cyl wall (even if it is imperceptible and hard to see).  So if it were mine i'd make sure to clean the cyl walls up with muriatic acid before honing.  Then IMO definitely go with a full top rebuild.  If you didn't chunk off any material, your lower (upper LOL!) end is probably OK.

Guess if it were mine I'd clean up the cyl walls with the acid and then send the jugs and head back to an expert like Rick to get spec'd out and reconditioned... have him send you new pistons, rings, gaskets.

Edited by MN Kitfox 2

Share this post


Link to post
Share on other sites

Posted

Actually, upon teardown, there was no piston melting- the RAVE valve hardware had loosened and allowed the slide to contact the piston.  It wore down the piston until it broke chunks off the rings, which then tore up the cylinder and head pretty good.  This made a hotspot that visibly failed the inner head o-ring, which pressurized the coolant and blew it all out the overflow tank.     The low coolant was a final symptom, not the root cause.  

The engine install is inverted- any thoughts on the chances that debris made it into the crankcase? 

 

 

 

IMG_20170902_153348.jpg

IMG_20170902_140100.jpg

Share this post


Link to post
Share on other sites

Posted (edited)

There is no way the rave valve can contact the piston... unless the wrong rave parts are installed.  I've had quite a few of these apart and am really sure about this.  The rave spring pushes it fully down where it seats in it's groove.

I know the rave looks to be really close to the piston but it does not and can not protrude into the cyl.

Oh man, yeah that looks like you had a bunch of crunching around there.  Maybe if it were a sled I'd take a chance, but if were mine, in a plane, I'd want to look in the case for debris... 

Edited by MN Kitfox 2

Share this post


Link to post
Share on other sites

Posted

Oh, you could push it a full, clear 1/8" into the cylinder.   The other cylinder is normal.   There's a nut on the threaded stud coming out of the end of the RAVE slide.   The shoulder of that nut is what actually contacts the stop and limits the travel of the valve.  If that nut loosens and rides up the stud, the valve can protrude further into the cylinder.    As I found it, the nut was loose and about 1/8" up the stud.  The valve had neatly and precisely cut/routed out a perfect little footprint in the piston, and the debris tore up the rest of the piston/cylinder/head, but I don't see any melt or other kind of damage. 

The engine backfired a few times right before I shut it down, and I think that blew off the RAVE valve diaphragm boot (and zip tie), but the rest of the RAVE valve hardware was undamaged.  (Well, the slide is beat up from eating away the piston, but I mean to say the rest of the RAVE valve hardware looked like it was functional) 

 

 

 

 

 

 

Share this post


Link to post
Share on other sites

Posted (edited)

Wow.  Guess they build them differently in the sleds.  Sure seems weird that they would make them more failproof in the snowmo engines.  The the ones I've worked with have a forged shoulder that stops travel (see pic below).

Man, I sure wish I could buy ya a beer, and I really do feel your pain.  Especially with a new motor like that...  crap.

But if the rave did it, then that helps a little i suppose.  You know that you found the problem and can get it right.

 

010-496 (copy).jpg

Edited by MN Kitfox 2

Share this post


Link to post
Share on other sites

Posted

Here's the style from my engine (unaffected cylinder).   You can see the stud and jam nut going into the actual blade of the valve.  If the nut and/or stud loosen, the valve goes further in... crunch.  

IMG_20170902_202244.jpg

Share this post


Link to post
Share on other sites

Posted

I'm guessing the rebuilder went through the rave valves right?

Everyone can make a mistake.... but hopefully he stands behind his work and takes care of you on this deal!

Share this post


Link to post
Share on other sites

Posted (edited)

If the valve is installed upside down (flipped over) it can also hit the piston.  Yes , I have seen this more than once in the snogo shop.  Sucks mr, I feel your pain.

 

It is kind of hard to tell from your pic, need a better one from the Id if you can but I am thinking the valve was in upside down.

Edited by akflyer

Share this post


Link to post
Share on other sites

Posted

Damn, I was really looking forward you flying the 670....I hope rick will do his best to take care of it QUICK.....

 

Share this post


Link to post
Share on other sites

Posted

akflyer, the image is of the undamaged side, and the valve could have flipped around any which way after I took it out.  I trust they were in correctly- the main failure is definitely the loose nut and the extra 1/8" of solid interference with the piston.  

 

 

Share this post


Link to post
Share on other sites

Posted

FWIW - a solution of Drano crystals (Sodium Hydroxide) and water will dissolve aluminum deposited on steel cylinder liners. And, modeling clay (Plasticine) will plug holes and keep the Drano from the aluminum casting.

1 person likes this

Share this post


Link to post
Share on other sites

Posted

Talked with the builder this morning and shipped the motor back; he's going to redo it all under warranty.   I'll start a new thread with (hopefully) better taxi test news when I get it back. 

Thanks everyone for all they help   

1 person likes this

Share this post


Link to post
Share on other sites

Posted

 That's good to hear!!!

Share this post


Link to post
Share on other sites

Posted (edited)

Talked with the builder this morning and shipped the motor back; he's going to redo it all under warranty.   I'll start a new thread with (hopefully) better taxi test news when I get it back. 

Thanks everyone for all they help   

WAS THIS ROTAX RICK?  Great to hear that someone stands behind their work.  Shit happens sometimes!   EDMO

Edited by EDMO

Share this post


Link to post
Share on other sites

Posted

Rick gets a ton of flack for being straight forward and what he wants you to do with the motors he builds. I have talked to him on numerous occasions and he's just a good ol boy from the south . If you've ever met anyone down here long enough you get how we are . I get along great with him and love hearing about the crazy stories he has from his days giving helicopter rides at fairs . Not a bad guy at all in my opinion just a little rough around the edges . 

Share this post


Link to post
Share on other sites

Posted

Rick gets a ton of flack for being straight forward and what he wants you to do with the motors he builds. I have talked to him on numerous occasions and he's just a good ol boy from the south . If you've ever met anyone down here long enough you get how we are . I get along great with him and love hearing about the crazy stories he has from his days giving helicopter rides at fairs . Not a bad guy at all in my opinion just a little rough around the edges . 

Seems like the people I get along with best are "just a little rough around the edges".

Ones that are smooth around the edges make me start to squint my eyes and sniff for the "politician smell"!

:BC:

 

2 people like this

Share this post


Link to post
Share on other sites

Posted

It is a Rotax Rick 670.  Mistakes happen, but I've been very pleased with his customer service and how he immediately stood behind his engine and offered to redo it.   I've enjoyed talking with him a bunch over the last year as we made a 670 happen.   Apparently about 2-3 hours of phone conversation is included with the price of a build-up :)

 

 

1 person likes this

Share this post


Link to post
Share on other sites

Posted

That sounds like Rick . 

Share this post


Link to post
Share on other sites

Posted

There is some really negative stuff out there in interweb land from just a small group of people about Rick. I've been talking with him for over 9 years now. He's loaned me tools for free and recently gave me a brand new stator in the box for half of what Rotax wanted for it. I now have 75 hours on my second rebuilt 582 and it runs like a sewing machine. Shit happens but what the person or company does to fix it is what makes them stand out from the rest in my opinion. Rick could have easily said well ya dun screwed up to half of the burned down motors that he get's back but he always fixes them and then makes an effort to educate the person on how to not murder their engine the next time around. At least this happened on the water and not the first time you were over the trees someplace.

3 people like this

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now
Sign in to follow this  
Followers 0