Biscuit

Hi all,
Can any help me out on the cause of the damage on my MCD Piston and cylinder, it was a brand new CY 29cc big bore kit have used them before with no problems. I ran the engine carefully for the first tank, but then I noticed it had lost compression, this is what I found. The piston has deep scores on it as well as the cylinder, the filter is brand new and clean, and the oil was King Cobra Venom (gold bottle) any Ideas ?
Thanks
Biscuit

Krets

I think i can see sand in the third pic? Can it be so?

badz

My Feedback: (1)

could be dirt, the piston sure has the signs of dirt marks on it. The cylinder and piston look really old to me, might have been a bad mix ratio also, looks like some straight oil sitting in the ports though. Definetly I wouldn't use that oil again it sure doesn't burn clean if thats only 2 runs on the engine.

sb racing

Looks to me like something has definatly got into your engine, If thats what it looks like after only one tank then i would'nt use the king cobra gold venom again, Change it for the king cobra silver venom. It will run much better and cleaner. my engine is spotless after every 8 hours use running on silver.

I hope this helps.

Si

Biscuit

No it was all spanking brand new, used the same oil in my FG no problems, and that is just clean oil i put in there to see if the compession would come up. It looks to me like its been running a bit hot, could that be it and its tried to seize ?? as it was new, kind of not sure what happend.[&o] could it be anything to do with the bearings braking up, as when I got the car it had been standing for a long while.
Thanks.

Bratch96

You say you noticed it had lost compression, what was it like running? What was it doing that made you open it up?

hathi

Were both the piston pin retainer still intact? From the first picture it looks like the retainer grove is worn down, not sure on this.

splcrazy

i reackon you got a bad cylinder head and it wasnt entirely smooth in there when it was machined , it looks like the edge of the ring has got caught on the edges of inside of the rough cylinder causing all the scrapings on the piston ...

and now looking at my own 29cc head kit i found that inside of the cylinder head on the exhaust outlet isnt smooth and has a sharp egde from the bad machining this caused my ring to grab onto it causing the ring to bend and jam and weld it self to the groove were the ring goes on . im gonna try and use my dremel to buff out this problem in my cylinder head and see how it goes

Biscuit

Well it started to race on tickover like it was lean, kept trying to get it to run richer must of unscrewed the high needle one turn but it was still the same. So stopped the engine and when I started it again I noticed it had lost compression even though it was running ok.
There was also a fair bit of grass stuck in the fins of the cylinder, might do away with the cowling next time, did it overheat? When I hear these stories of the CY big bore kit it makes you feel like just putting the Zenoha 26 back on, its just when I put one on the FG it was so powerfull.
Thanks
Biscuit

Dr.ArmoMaxx

Thats not a new engine with 1 tank....Look at that carbon build up...

Something dirt was in the engine. You gonna need new piston/head.

Nathan9492

Ouch dude that looks terminal [:@]

dgav407

I have not seen that much damage in an engine installed in an MCD car before - the engines normally (although rarely I must add) seize as a result of a tight spot on the right hand side of the exhaust port. The engine clearly having overheated.

Don't bother with big-bore engines or even tuned/race engines in an MCD car, a standard (unmodified) CY or Zenoah 26cc engine is by far the best option, especially if you use a Samba tuned pipe. The cars are very hard on engines and even with all the side and rear windows removed from the bodyshell they still run on the hot side. If you get the gearing, oil type, oil mix, carb settings wrong you will end up cooking an engine. I don't recommend using a standard CY or Zenoah clutch without a hard clutch spring - otherwise the clutch engages way too early which puts an additional strain on the engine.

Now before anyone thinks I have an issue with MCD cars, I don't. I actually own and race both a Race Runner and a Rally Car and can thoroughly recommend them. The problem is that engine wise they will not take the same abuse as say FG, HARM, HPI Baja 2WD drive cars.

If you think that using a standard 26cc engine for racing would result in an uncompetetive car, it is simply not the case. At a largescale off-road racing meeting here in the UK last weekend not only did an MCD Race Runner win the event but the top qualifier (by 18 seconds!!) used a standard 26cc engine. These were being raced against some of the top off-road racers in the UK who were using top-spec all alloy european 2WD cars with Oddified, Alro etc tuned engines.

TheFgMan01

^ Good info [sm=thumbs_up.gif]

Biscuit

Your right that is good info, all those things could of happened to me, as it was a new piston and liner and the gearing was a bit high, and there was not a lot of airflow over the motor. My car is a Blue Line, completely renovated, with a nice new Subaru shell, and guess what ? the windows are not cut out, I have bought a second hand Megan Renult shell that has been cut out and will use that and save the subaru. So I will be more carefull in the future, run it in carefully and gear it down. I had none of these issues with the FG 29, it just runs and runs so thought these motors are kind of tough I guess not. And to the guy who said its not new well it was new because I fitted it!! plus I run an adjustable clutch, you have to give it a load of throttle to pull away but it keeps it in the power band and it really moves off the line. Maybe change the oil from the gold bottle to the silver, can anyone give me the gearing for the rally car for off road, flat grass?? Thanks very helpfull post, having trouble getting the 29cc so may have to go 26. Will post a few pics of the clutch as not sure what it is.
Biscuit

dgav407

Biscuit

The clutch is probably an FG one - I have used a similar one but with mixed results. I am now using lightened Zenoah clutches and they seem to engage at about the right point plus they are showing little sign of wear.

The gold King Cobra oil is okay for MCD cars providing you are prepared to clean the inside of the engine on a regular basis and not just when you change the piston ring.

Rally Car gearing - for a standard 26cc engine I would start with a 30 gear on the clutch bell and a 33 gear for the spur gear. A 25 gear behind the 33 gear on the gearbox central layshaft and a 24 gear on the central diff layshaft. For extra speed swap the 30 and 33 gears.

The latest MCD spares catalogue includes a gear ratio chart and can be downloaded from http://www.kingcobra.co.uk/news/MCD_Catalogue_2007.pdf

Clive

Biscuit

Cheers Clive, I was running with the 33 on the clutch, I kind of liked the clutch, brand new spike tires on grass spins all for wheels pulling away, standard clutch just bogged down the motor. Anyway a few more pics of my self made gear carrier, and maybe another pic of what may of caused the problem, how can I stop this.
Steve.

dgav407

Biscuit

Nice gear carrier - that should in theory help with engine cooling, although the grass under the plastic engine cover would have restricted the airflow from the fan and certainly increased the engine temperature.

You will need to make some plastic/lexan mudguards for the front wheels. For the new Proline cars it is possible to buy an inner bodyshell - this will keep out grass, dirt, water, snow etc but will restrict the airflow to the engine. King Cobra make an alloy radio plate shield (http://www.kingcobra.co.uk/news/newsitem.php?id=556) although I am not sure that design would work in your case.

I have only briefly run my Rally Car off-road (and that was by mistake) and had no problems with grass but ended up with a car full of stones!

Clive

Biscuit

Yeah I bet they would wreck the gears, and all that nice blue alloy, I must say when it was going it was a beast, but I have had a fair few problems, one with the radio, (moduel in back of 3cv) 2 runaways with big damage, then wired the RX cells round the wrong way and fried 3 expensive servos, then had the shell sprayed, and first time I used it the paint fell off, then the engine died. Sort of wish I had kept the FG.[&o]
Thanks for the Replies.
Steve.

cyclops1970

My Feedback: (5)

[quote]ORIGINAL: Biscuit

Yeah I bet they would wreck the gears, and all that nice blue alloy, I must say when it was going it was a beast, but I have had a fair few problems, one with the radio, (moduel in back of 3cv) 2 runaways with big damage, then wired the RX cells round the wrong way and fried 3 expensive servos, then had the shell sprayed, and first time I used it the paint fell off, then the engine died. Sort of wish I had kept the FG.[&o]
Thanks for the Replies.
Steve.
[/quote
if you wanna trade i have a 100% alloy MB i might want to trade for the MCD ?

kennyrccars

To increase engine cooling cut the plastic cover like this. Alro, Oddie etc all do this, works a treat...