zen 260 turned down piston

zen 260 turned down piston
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zen 260 turned down piston - 6/13/2009 4:39 PM

wildman51

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Looking into getting a zen 260 for my rio talked to the guy at the lhs and he recomended that I have the piston turned down to keep the engine from siezing up is this a common practice for zen motors he said he could do it for 6.00 extra but I dont know about going into a new motor .any thoughts on this thanks...................wild

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RE: zen 260 turned down piston - 6/13/2009 7:56 PM

SJN

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I think the zenoah is one of the most reliable engines you can get stock.

I would not change anything.

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RE: zen 260 turned down piston - 6/13/2009 9:38 PM

Bbbutch

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The Zenoah motor is a very reliable motor but if you are going to run it hard (and who doesn't) the piston does need to be turned down about .010 for the first 7 to 8 MM from the top. This will keep the piston from scaring or worse, seizing in the cylinder when things gets very hot.
Think about it. There has to a reason why every piston (I've seen) in a modified Zen motor has this modification.

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RE: zen 260 turned down piston - 6/13/2009 10:07 PM

martno1fan

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There is no reason to have it done to a stock motor .
Mart

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RE: zen 260 turned down piston - 6/13/2009 10:58 PM

Nosedragger

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There are dimensions and full details on MGB.com about this procedure, not doing can result in in a galled piston and possible scored cylinder which would need to be relaced along with the piston.

Motors stock or not all need this done.

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RE: zen 260 turned down piston - 6/13/2009 11:17 PM

martno1fan

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Ive never had it done on my stock motors and never had any scored cylinders or seized motors ,the main cause of these problems come from when people start messing with the motor ie opening ports and modding them.That said i bet theres more blown cylinders caused by mods done to motors than from leaving a stock motor alone.
Mart

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RE: zen 260 turned down piston - 6/13/2009 11:24 PM

Scott Schneider

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.010"

is way too much !!

The under cut of the pistons upper 5/16" ( 1/8" above ring and @ 3/16" below ) needs to ONLY be a .002" cut reducing diameter .004" total.
Any more than this will lead to excessive piston rock and carbon build up on sides of piston.

If your are NOT racing your boat within a STOCK class, then I WOULD have it done !

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RE: zen 260 turned down piston - 6/14/2009 12:36 AM

Nosedragger

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quote:

ORIGINAL: martno1fan

Ive never had it done on my stock motors and never had any scored cylinders or seized motors ,the main cause of these problems come from when people start messing with the motor ie opening ports and modding them.That said i bet theres more blown cylinders caused by mods done to motors than from leaving a stock motor alone.
Mart

Thats not correct. The main cause of the problems is piston to wall clearnace.Has nothing to do with the ports.

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RE: zen 260 turned down piston - 6/14/2009 12:48 AM

wildman51

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thanks guys for all the input but Im still a little confused Im thinking that if its new then leave it be but I do want whats best for the motor thanks

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RE: zen 260 turned down piston - 6/14/2009 1:04 AM

Nosedragger

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If you can get it done for 6.00 it will save you 15 for the piston, 5 for the ring 34 for the jug 1.50 for the base gasket.
$55.50 is what it can cost if its not done.
As for warrenty the zen warrenty is only good for 3 months from purchase.and they won't warrenty service damaged pistons and cylinders, they refuse to acknowldge this condition as a defect in manufacturing.

your call.

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RE: zen 260 turned down piston - 6/14/2009 1:14 AM

Scott Schneider

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For the Uninformed or Misinformed .......

What causes the siezures on unturned pistons is known as a "Cold Siezure" It is generally caused by an engine being run really hard before it has warmed up. Being the cylinder is water cooled and if run hard with no warm up time has NOT expanded at all and is fairly cool.
Piston on the other hard will heat up very quickly and expand its diameter slightly under the spike of heat generated.
The lessened running clearance between the piston and cylinder in this situation cause the siezure.

FYI ...

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RE: zen 260 turned down piston - 6/14/2009 3:20 AM

Bbbutch

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.010 is the total cut off the diameter of the piston. That would equal .005 per side. 5/16" equals 7.9 MM. I think we are talking close to the same thing here. This is what I turn my pistons down to. I have simply copied the pistons that I have purchased from WWH and Oneil Borthers.

OPPS! That was a stock piston I purchased from Oneil Bros. The other one was from American RC and just looking at it (I don't have my mic handy) I would have to guess it only has .002 to .003 removed per side.

< Message edited by Bbbutch -- 6/14/2009 4:23 AM >

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RE: zen 260 turned down piston - 6/14/2009 4:19 AM

wildman51

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thanks Im gonna talk to the guy tomorrow and see how much he is gonna shave off still dont like the fact of going in to a new motor ..is the replacment piston turned down I found the motor for 205.00 with a 257 carb free shipping is this a good buy thanks guys for all the input

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RE: zen 260 turned down piston - 6/14/2009 11:37 AM

martno1fan

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I can only talk from my experience and i have NEVER had any of my stock pistons modded in the 3 yrs ive been running them and have had no issues.I dont race and that might have some bearing on it but to be honest i believe if you run your motors in propperly from new,run plenty of oil then you wont have any problems,over cooling your motor could be an isue as can too little.If you can get it done cheap and it gives you peace of mind then do it but i wont be going out of my way to have any of mine done now or in the future.
Mart

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RE: zen 260 turned down piston - 6/14/2009 1:22 PM

wildman51

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thanks mart I think Im gonna go stock and longevity of the zen thanks ...........................I just want a good running boat without all the hassel of rebuilding the motor every 2 or 3 tanks of gas thanks guys for your input I have learned alot

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RE: zen 260 turned down piston - 6/15/2009 1:14 AM

glennb2006

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I'd get it done if I were you, especially for only $6 extra, as Scott mentioned, the issue is when the engine is not fully warmed up, bear in mind that the Zens are designed as air cooled motors which run pretty hot, we then water cool the cylinder, which, as a result, is considerably cooler then it is designed to be, so some relief to the running tolerences makes sense.

Ignore Mart, his motors don't seize as they only run at 3000 RPM!!

Mart - I am only having a laugh....

G

< Message edited by glennb2006 -- 6/15/2009 1:15 AM >

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RE: zen 260 turned down piston - 6/15/2009 5:01 AM

nvs motorsports

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Does mart run diesels

Couldnt resist

By the way Schneider is on the money with his info
But if you want just make sure you warm up properly and use good quality oil in fuel

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RE: zen 260 turned down piston - 6/15/2009 6:51 AM

DaveMarles

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Stock or not you should get iot done. It does no harm and could save you a big rebuild cost.

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RE: zen 260 turned down piston - 6/15/2009 8:32 AM

martno1fan

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quote:

ORIGINAL: DaveMarles

Stock or not you should get iot done. It does no harm and could save you a big rebuild cost.

If thats the case why do you sell stock motors with stock pistons Dave? you never once mentioned to me when i bought two motors from you that this was an issue?.I agree it does no harm but is this really such a big issue?if it is id have though it would be nice to have been told at the time.That said ive never heard of many having this problem certainly not with a sports boat and a stock motor.I still say use good oil run them in and warm em up before you hit wot and you will be fine.Oh and as i said before DONT over cool them.
Mart
Glenn very funny mate id back my SS motor against any other out there as regards power and reliability.

< Message edited by martno1fan -- 6/15/2009 6:58 PM >

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RE: zen 260 turned down piston - 6/15/2009 1:16 PM

thevirginian

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First of, Scott Schneider is right on the money with his comment. The problem is not Zenoah, but the marine application of this motor. It is a converted Chainsaw engine. Converted for marine application. Especially running in very cold water can lead to these extreme expension differences of the piston and the cylinder. I know a guy who ran his brand new RTR gas boat and seized the motor onhis first run. After he received his repaired motor back he seized it again. Nobody told him about the benefit of the relieve cut. After he had it done, no more problems. I turn my pistons down by 0.06-0.08mm. Don't forget one thing: we run those motors WOT most the time and the generated heat is quite high. So why take the chance?

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RE: zen 260 turned down piston - 6/15/2009 2:01 PM

dicko

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Speaking from experience, I've had a stock motor seize & score, I'm not sure if it was because of the oil I was using, or the fact that the top of the piston wasn't turned down. Since It happened, I have swapped out to Castrol A747 oil & had the top of all my Zens (stock & mod) turned down. I'v never had an issue since. I was previously running Castrol TS2 oil.

just my $0.02

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RE: zen 260 turned down piston - 6/15/2009 3:28 PM

Nosedragger

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quote:

ORIGINAL: martno1fan

quote:

ORIGINAL: DaveMarles

Stock or not you should get iot done. It does no harm and could save you a big rebuild cost.

If thats the case why do you sell stock motors with stock pistons Dave? you never once mentioned to me when i bought two motors from you that this was an issue?.I agree it does no harm but is this really such a big issue? ive never heard of many having this problem certainly not with a sports boat.I still say use good oil run them in and warm em up before you hit wot and you will be fine.Oh and as i said before DONT over cool them.
Mart
Glenn very funny mate id back my SS motor against any other out there as regards power and reliability.

Its not an issue, its $6 versus $55.50 for $6 you can have peace of mind that you won't have problems, without it you throw the dice on $55.50 and you better beleive if it happens you'll spend the $6 on the replacement.
Advising people not to take this precaution is bad advise. When wildman loses his piston and cylinder you'll refund him the cost of the replacement parts?

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RE: zen 260 turned down piston - 6/15/2009 3:50 PM

martno1fan

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My point is this if boat outlets and engine builders are selling motors to us without doing this mod and then they come on forums saying its necesary to have it done then to me that is not good.Theyre the ones selling these motors to us and if there is an issue that needs adressing then theyre the ones who should do it before selling them to us.I still say though that i know of no one that has had this problem on a stock motor,id bet theres more guys running them stock without turned down pistons than with so i say the problem is probably more to do with how they treat them ie breaking them in or not and using the incorrect oil and poor cooling setups than anything else.
Mart
as regards refunds then i say if a boat outlet sells you a motor and it seizes up and they then tell you its because the piston needs to be turned down then they are the ones in the wrong not me.

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RE: zen 260 turned down piston - 6/15/2009 5:35 PM

thevirginian

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mart,
I think you have a legitimate point with what your are saying. The majority of Zenoah users are probably not even aware of the risk they are taking for not having their pistons turned down. I don't think there is anybody out there trying to say that without the piston relieved a problem is imminent. But the possibility of a seizure is definitely greater for a stock piston, periot.

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RE: zen 260 turned down piston - 6/15/2009 6:12 PM

martno1fan

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Thats my whole point though if there is a risk then the guys selling these motors should make the buyers aware of it,i have never been notified by any of the sellers about any possible issues with using the motors stock.That said ive not had any problems with 3 stock motors but i followed strict run in methods unlike most that ive seen on here.Im not saying i think its a bad thing to have the piston turned down,but as i say never had a probelm personally and not once has any engine supplier made me aware of any possible issues with the stock piston, if thats the case why didnt they tell me when i bought the motors?.Would they have given me a refund if id had a problem ? i doubt it.
Mart

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