piston scratches

[pepper]

hey guys, my c-spec has some major scratches on the piston. looking throught the exhaust and turning slowly on the crank i can see air and bubbles comeing from where the scratches are.. it just sucks!!

hent: don't fly in the sand upside down close to the ground!!

so where do i send this thing to get a new liner, piston, ring, etc?? or is it ok to do it my self?

pepper

[capebob]

Pepper,
It's easy enough to do it yourself but make sure you really need to. Your c-spec is a ringed engine and the condition of the piston has little to do with compression. Compression is determined by the condition of the ring and sleeve. Most piston scratching is caused by the engine running too hot and swelling enough to contact the sleeve. I suggest that you disassemble your engine and inspect the condition of the sleeve before you order parts. Any hobby store can get the parts for you or you can order direct from the importer, Great Planes/Tower.

It doesn't sound like you've disassembled an engine before. First remove the back-plate and cylinder head. Then with the piston at bottom push a soft cloth in through the exhaust port and pull a length of it into the cylinder. Then gently turn your crankshaft and when the piston pushes on the cloth the cylinder sleeve will start up. When you can get your fingers around it remove the cloth and finish pulling the sleeve. Once the sleeve is removed it is easy to remove the piston. Caution, some pistons must be installed in one direction so make sure you make a note of which way yours is installed. When reassembling, first install the piston and connecting rod assembly then install the sleeve. You will note that the bottom of the sleeve is chamfered to make the job of getting the sleeve down over the piston easier.

I hope this helps.

Bob

[pepper]

no i haven't. if it got bad i just got rid of it and got a new one. i decided to go ahead and do it myself this time and not be lazy about it..

thanks for the info!!

pepper

[pepper]

ok, i got everything out. my piston ring will not move around and i am afraid that if i try to take it off i will break it??

aslo something concerns me. at the bottom of the piston where it rotates, their are scratches on the bottom of the cyl as your looking in where the backplate goes..

pepper

[capebob]

Yes, you will probably break your ring if you try to remove it. Piston rings in our engines get rather brittle with use. It shouldn't move around because there is a key where the ring ends come together so that the ring can't be moved around. If the ring is stuck in the grove (a sure sign of overheating) you may be able to free it by pushing gently with a finger nail. Are the scratches on the crankcase where the connecting rod rotates? If this is the case your rear bearing is shot and the connecting rod is making the scratches.

Bob

[pepper]

the ring came loose just as i plucked it with my nail. no problem there.


right. on the bottom and the sides of the crankcase. no major scratches but small ones.

do i need to order a rear bearing?

after i pulled everything out the piston seems to still have good compression and rides real good on the sleve. the sleve itself has small scratches on the exhaust side but the piston and sleve are very clean on rest.

have they come out with a new bearing or do i have to just keep replaceing this one? :(

peppa

[capebob]

Peppa,

I have replaced all my big block rear bearings with bearings from Boca Bearing.

http://www.bocabearing.com/

My OS 50 was going through bearings so fast I could hardly keep up. I replaced the stock bearing with a ceramic from Boca. It was pricey but I haven't had any trouble with it since.

Bob

[pepper]

sweet!! you are tha man!!

pepper

[pepper]

ok, just took a look at the web sight, please tell me you have a part#.. that stuff reads JAP to me..

[capebob]

I don't have the part number for the c-spec but give them a call:

1-800-332-3256

Bob

[pepper]

i was looking at towerhobbies for the replacement of some of the engine parts.... are these things made of gold or what..

liner-73.99
piston-41.00
rear bearing-21.49
Boca bearing- at least 40 for high speed.


anyone know of a cheaper place?

pepper

[capebob]

You may get a dollar of two off Tower's prices at online stores but don't expect much. Kit margins are so low that shops need to get near full retail on parts to keep their doors open.

Bob

[Matthew]

Pepper

HeliProz.com sell all that stuff to I think. Except maybe not the Boca bearing. have you tried them for a price.

[pepper]

just checked heliproz. it seems to be about 4 to 10 bucks cheaper..

pepper