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Stuck contrapiston?

Old 07-01-2013, 03:09 PM
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franchi
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Default Stuck contrapiston?

Hi Gang:

I started working on my new MARZ 2.5 Diesel today and found that the contra piston was too low to allow the engine to turn over.

I disassembled the engine and cleaned all of the parts. The contra piston is tighter than a frog's butt! I tried to move it by tapping it with a hammer and a wooden dowel. No luck! The contra looked rusty or had dried oil as an adhesive.

I guess that I will attempt to heat the case and try the wooden dowel again. Should I remove the contra from the bottom or the top of the cylinder?

If I get it out, I will clean the cylinder and contra slightly without removing any metal.

To fit the contra to the sleeve, should I taper the sleeve from the bottom to the top or carefully remove a very SMALL amount of metal from the contra.

Oh yes, there was no way that I could remove the crankshaft. I guess a large press would have done it but ... Lol I have heard that the crankshaft to bearing fit on these engins can be very very tight. Sometimes the shafts are smoothed down until a good fit may be acheived.


Any suggestions?

Stay well

Franchi

Old 07-01-2013, 03:44 PM
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Recycled Flyer
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Default RE: Stuck contrapiston?

Heat gun and drive the contra down.
Old 07-01-2013, 03:54 PM
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Default RE: Stuck contrapiston?

Franchi

If you do a search on this forum on 'stuck contra-pistons", you will find a few threads with some very helpful advice.

Do make sure to tap it down the bore to remove it.
Old 07-02-2013, 12:56 AM
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controlliner
 
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Default RE: Stuck contrapiston?

Heat and move it to the top of the liner. Do not remove it.........you may regret it for a long time. Especially if it fits the cylinder real intimately and you have no way to install it back in true to the bore. You may never get back into the bore without cocking it up. Ask me how I know. I have manufactured a fixture "out of 1010 steel" for removing and installing contra pistons to keep it true to the cylinder bore.
Old 07-02-2013, 05:09 AM
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franchi
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Default RE: Stuck contrapiston?

Hi:

Thanks for all of the replies!

I did do a search and I did not find any help as to how to remove the contra, There was a lot of talk about stuck contrapistons but none that helped my situation.

The contra appears to be near the top of the sleeve save about 1/32" This thing is really stuck!!!

I have had it soaking in penetrating oil for about 15 hours and I will heat it with a torch to see if i can get it to move today.

I like the tip about not removing it from the cylinder! I can see very bad things in my future if I did this! Lo

I will keep you posted as to my progress or lack of it.

From this post, one may deduce that I have I trouble today! Lol

Stay well my friends,

Franchi
Old 07-02-2013, 05:23 AM
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Default RE: Stuck contrapiston?

When you heat it, just heat it enough to "smoke " the oil off the cylinder. Do not over heat the steel. You might have better luck letting it sit in an old pot of boiling water. I can't stress it enough not to overheat the steel. 350 degrees F. is enough heat. or 212 Degrees as is boiling water. Be gentle.
Old 07-02-2013, 11:28 AM
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Default RE: Stuck contrapiston?

Use a gear puller that u can get from an auto parts store. put a wooden dowel in the cylinder and force it up to the top of the cylinder. Do not remove it! A tight fit is a good thing!

Max
Old 07-02-2013, 02:16 PM
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Default RE: Stuck contrapiston?


ORIGINAL: franchi

I did do a search and I did not find any help as to how to remove the contra, There was a lot of talk about stuck contrapistons but none that helped my situation.
http://www.rcuniverse.com/forum/m_10...m.htm#10219485



"The main aim with a stuck contra-piston is to MOVE the thing, either up or down. Once this is done and lubricant can reach the infinitesimal gap twixt the cylinder walls & the contra, then it will again move smoothly. Tapping the contra down has 2 advantages, 1) the bore in a Diesel is usually tapered inwards towards the top, thus as the contra comes down, it gets looser, and 2) trying to force a stuck contra-piston up by using the other mechanical parts of the engine puts IMMENSE pressure on the rod, crank-pin & crank-web. As this particular engine would not be stuck as tight as say, a 50 year old Diesel which is NIB, it should be possible to free it up quite easily by tapping the contra down, then squirting some oil down the compression adjuster hole so's the contra will then be sliding back up on a lubricated surface. Speaking of old Diesel's that have lain in their box for decades un-run, I have seen the thread in the alloy head stripped out, merely by forcing the adjuster to turn whilst trying to move a stuck contra-piston. This gives you some idea of the forces involved in trying to get a contra-piston to move !"

http://www.rcuniverse.com/forum/m_34...tm.htm#3424198

"You did not say if the engines are new or used. If they are used the contras may be held tight with castor oil. As mentioned, try hand starting them first. With the screw turned out some, a "pop" may move the conra. Since you have turned it in, it may backfire until it pops back to running position.
You might also try squirting a little fuel in the cylinder with the engine inverted and let it sit for awhile to penetrate.
Some contra pistons will not move at operating temperature. Sometimes richening the needle will cool it off enough to make the contra move. Other times you must let it cool.
If the contra is far enough into the cylinder to not allow a "C" clamp, removing the cylinder and pushing out the contra with an appropriate sized dowel will work. Make sure the cylinder is sitting on a block of wood instead of a hard surface. Also make sure you are tapping the dowel in the center so the contra won't try to tilt.
If it IS an engine that has been sitting around, while it is apart make sure the conrod is not stuck to the wrist pin in the piston.
With the contra out, clean around it with some soapy water and fine steel wool (or a Brillo pad). Do the same inside the top of the cylinder where the contra sits.
Look tor any scaring on the contra and cylinder that might cause a bind. If any is found, a little fine crocus cloth should repair it. DON'T OVERDO IT.

If the engines are new, I would try letting them sit inverted with fuel in the cylinder for a couple of hours then try to start them and see if the contra will "pop" back as above. You have to be able to adjust them when running but otherwise, tight is good."

http://www.rcuniverse.com/forum/m_39...tm.htm#3973884

"You've recieved some good afvice, but may I offer a couple of alternative suggestions for freeing up the contra-piston that might well work and preclude pounding on anything with a hammer?
You said you have some old fuel that is suspect. Turn the crank to BDC. Remove the tommy bar completely. (T bar that adjusts the compression) Put the engine in a glass container that can be sealed tightly. pour in enough of the old fuel to cover it completely, cap it tightly and do other things for a few days or weeks. After it's had a long soak see if it will move. If it's still being stubborn break out your heat gun and get the cylinder head/cylinder hot enough to be quite uncomfortable to touch. That will usually re-liquify hardened castor enough to allow things to move. If none of the above work there's still the hammer.
I've had VERY good luck with the anti-freeze in a crock-pot method. So far I haven't yet had an old engine refuse to come unstuck after 24-48 hours of soaking in the hot anti-freeze, but I haven't tried it on a stuck contra-piston either so you're on your own there.
BTW, even if you get things freed up it's not a bad idea to use the heat gun to keep things free while trying to start the engine. I have had contra-pistons stuck so badly that they refused to move after starting. That can do bad things to rods and cranks. "

Franchi, surely there is something that a search (as above) that will prove of assistance?

Personally my Marz had the only the sharp edges (NOT the lapped surface) relieved by some 1200 wet and dry paper soaked in engine oil and this helped immeasurably .


Oh, and the crankshaft sanded beck around the main bearing as it was an EXTREMELYtight fit.

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