Seized Engine

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shade82000

Member
Messages
12
Location
St. Albans, Herts
Hi everyone, I was looking for a dedicated forum for largescale cars and I came upon this one!

OK I was out running my Baja SS today and I seized my engine. First the spur gear got shreaded and I opened up the throttle to adjust the needles a bit for the next run and the engine just died.

I've just read in a manual for another engine that these petrol engines should not be allowed to WOT when there is no load. I won't be doing that again.

I managed to take the head off and there was a 1/2in x 1in score mark on the cylinder and piston, also the piston ring was damaged.

The spark plug was a matt grey colour.

I got a 29cc head a couple of months ago and it came with a 2mm stroker crank.

If I put the original head & piston back on then will I be able to keep the same crank/conrod or should I completely take the engine apart and put the original crank back in?

If I keep the current one in then will I gain or lose power, or will it just not work at all?

Also, would the engine have got too hot because it was running too rich or too lean at high RPM? I always get it the wrong way round with petrol engines.

Cheers!
 
OK what 29cc topend did you buy? and did it come with the 2mm crank as an option? or did you just purchase it as a matter of having it on hand?


alot of what gaskets you use will depend on what topend kit you bought. if you don't use the right combination of items. you may not get it to run, or it will run but like poop, or you ll have the piston possibly hitting the dome of the cylinder.
 
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Hi,
I bought a chung yang head with a 2mm stroker crank. It came with a 0.020in gasket because the top of the cylinder had been machined to account for the longer stroke and therefore a 0.040in gasket was not required.

I think when I re-use the original head, I can keep the 2mm stroker crank as long as I put a 0.040in gasket in there or I will run into problems like you described.
 
The spark plug was a matt grey colour.
Click to expand...

If your plug was grey then you're too lean which will get hot and seize your motor...which is what happened.
Start at factory settings on the carb 1 3/8 H and 1 1/4 L and use very small adjustments from there. Check out this link...real helpful http://www.youtube.com/watch?v=6tMUfbQCzI8
For your motor rebuild use the head you have put a 40thou gasket in and check your squish by putting a bit of bent bit of soldering wire down the plug hole and over to one side (you want about 10mm past the edge of the edge of plug hole) slowly crank the engine over top dead centre...the solder will squish between the piston and head..pull it out and measure with vernier or micrometer.. you want no less than .017 for a new zen.
you'll have a 27.2 stroker....
 
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i take it you got the ESP Modified 30.5 topend kit that come with the 2mm stroker? if so use that kit WITH the 2mm stroker. you could use a 1mm stroker crank and NO cylinder gasket, just a good sealer.

but if you did infact buy the ESP 30.5 and 2mm crank setup, install that and enjoy. like has been said, start RICH and slowly tune up. Follow ESPs tuning guide and you should have better luck. make sure the carb manifold and gaskets wernt leaking or a loose cylinder/spark plug and even exhaust bolts can help cause a lean sieze.
 
This all sounds a bit complicated, I no longer have the head or piston as they seized, and I don't know if I can buy them again separately without the crank, or if I can get another large bore head from another company that will work with my stroker.

I'm at work right now so I can't access ebay but when I get home I will post a link to the ebay listing where I got the bore kit from.

It does seem logical that it could have been running lean because after the blow, I had no problem at all taking the spark plug out, it was loose about 1/4 turn already. I'm not sure though, this might have been caused by the actual seizure or it might have vibrated loose while running the car. I run a lot of nitro cars and I remember being told that the opposite applies to petrol engines, ie. they run cooler and bog down when they are lean and they run hotter and faster when they are rich. I don't know if this is true because it was only one person who told me.

Cheers for that tip mooman, I will definately use it when I have got all my gasket sizes etc worked out and get round to the rebuild. I don't have the tools to measure the solder thickness yet but I suppose having the right tools is a small price to pay compared to engine failure!
 
do me a favor. Post a link to the Kit or motor that you Siezed up or provide its full specs, ie, case brand, crank used, topend used, carb used ect....... and then post a link to the topend kit you have/want to get on its way to you, or what exactly you want out of the new topend.

I think im confused as to what motor you siezed, and what topend you have/want to replace it.

a loose spark plug (ANY air leak for that matter, including pin holes in your fuel line) can and will certainly help to lean sieze a motor (fwiw, Lean sized does not mean STUCK PISTON and is Siezed, ie fused together and wont move) rather lean sieze is the term used with these motor have been run too lean, which creates too much heat, and literally starts to melt the cylinder plating off the cylinder. I m betting if you were to look at the siezed topend, you would see s Severe scorch mark at the bottom right hand side of the exhuast port (viewing from thru the exhaust port) and likely a small spot 180 * on the opposite side of the cylinder. and matching piston scorching as well.

the loose plug likely allow additonal air to be sucked into the cylinder on the down stroke. more air into the after carborated mix, is a leaner ratio. a lean air/fuel ratio is the root cause of lean siezures.


thanx
Tim
 
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Here is a link to the ebay listing where I bought it from.

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=230299461326

I put this stroker/topend on and this is the one I seized. Now I am thinking about putting the original head /piston back on and keeping the upgraded crank (because taking the rest of the engine apart is a pain). if I did this then I would need to consider the correct size of gasket to use.

Note that the one I seized had been machined at the top of the cylinder so it will take a standard 0.020in gasket.

I am assuming that I could also get another big-bore head and if it has been machined aswell then I use a 0.020 gasket but if it has not been machined at the top then i use a 0.040 gasket.

Thanks for your info on seizures though, if I understand what you are saying correctly then this is probably what happened. I can't get to the engine right now but I know that the marking on both the piston and cylinder are almost exactly on the opposite side to the notch/gap on the piston ring.

I have a K&N style mesh filter which is going to be replaced with a TGN Redneck. Also I had a couple of those boost bottles on there but when I rebuild it I am going to use a reed valve which would render the boost bottles pointless, if they ever did work in the first place.

The carb is standard tho.
 
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OK, I just checked the marks on the head and piston, it is exactly as you describe.

Looking through the exhaust port there is a bad scorchmark over the far right hand side of the exhaust port (1 1/2in long and 1/2in wide).

There is also a not so heavy scorchmark over the left hand side of the intake port (1 1/2in long, 1/4in wide). They are dead opposite each other.

There are matching marks on the piston.

It must have been running lean because of the loose spark plug. I will check these things in future before every run.

Looking up through the bottom of the head, I also noticed an odd pattern of six dots in a hexagon shape around the spark plug hole. I'm didn't see these when the head was new, I seem to remember the whole of the inside being very clean and shiny.
 
yea, those are Classic signs of lean sieze. the opposite side (by intake) takes a hit becuz the exhaust side got so hot, it expands a bit in that area (the serverly scorched one) and it literally Pushes the piston into the opposite wall.


If you use the stock topend on a 2mm crank, you will need to Stack the cylinder gaskets. a single .040 gasket will not clear. you will actually need .060 of clearance. so a .020 AND a .040 gasket is needed, or 3 .020 gaskets (two is bad enough, don't do 3. and use COPPER ONLY for stanking. you need both gaskets to get the squish clearance needed (aournd a .018 clearance i think is about optimal). and using a paper gasket/s to stack will likely cause the head to not set Flush and will be more likely to leak.) use a GOOD gas rated sealer between the cylinder/case/ and gaskets to seal them up. THIN THIN layer, but covering layer. don't want to put TOO Much on and squish out a shitload to the inside of the motor as you torque the cylinder bolts.

its Very important to not OVER torque them either. i think they are speced at 5 ft/lbs of torque for the cylinder bolts. over torquing them again causes things to not line up correctly, and can acually cause the cylinder to bow a bit due to overtorquing.


ok you bought and installed the CY29RC topend. 35mm bore with 30mm crank. hate to say it, but thats the WORST topend to work on/with. Why anyone (not you but the people who Mod this POS) would do additional work on that piss poor topend and sell it is beyond me. out of all the cy stuff, that one is just the shitbottom of the barrel.

if you want my opinion, which im sure most could give 2 shits less about it, lol, these are the topend kits you want to chose from.

first is the good old fashioned Zenoah 26 topend kit.
http://www.davesmotors.com/s.nl/c.885035/n.1/it.A/id.4164/.f

then the stock cy GP290 topend (36mm bore, likely the BEST cylinder CY offers and the only one made by CY worth spending modding money on).
http://www.davesmotors.com/s.nl/c.885035/n.1/it.A/id.4170/.f

either of these to above motors will need you to stack gaskets to clearance for the 2mm stroker crank.

imo, the more appropriate options are below.

Next is the ESP modded 27.2 NON PORTED topend (this is the same topend as above Zenoah one, but has been modified by ESP in the dome area to allow use of 2mm stroked crank with a single .020 cylinder gasket.
http://www.davesmotors.com/s.nl/c.885035/n.1/it.A/id.4756/.f

(note: you have to ORDER The 2mm stroker crank, though it is pictured, its not part of the 99.00 price shown. so you can get this topend for 100.00 and turn your current case with 2mm stroker into a 27.2 Non Ported topend while using one .020 cylinder gasket).

Same goes with this kit but instead of a 27.2 it would be a 30.5
http://www.davesmotors.com/s.nl/c.885035/n.1/it.A/id.4169/.f

ESPs work it TOP NOTCH and most of the work done is now by CNC and cleaned up by hand). but even when Doug was hand porting all the kits. his repeatabilty was hard to match. you could buy a Ready to install ported beast form ESPk, and if you granaded the topend, buy a new one from Doug and the replacement would run basically identical to the original Motor.

both of these above kits only use one .020 cylinder gasket to clearance for the 2mm crank you have installed (both show the 2mm storker, but niether comes with the kit, its a seperate add on when you order. so just order the one you want, as you already have the stroker installed).


and whenever you have a catastropic failure of a motor, whether is from ingestion of sand, dirt/ ball bearings thru the carb, exhaust, plug hole, whatever. ALWAYS tear into your case in do a internal inspection. ESPECIALLY if things were loose. dirt, grime and filth can hide in some deep corners of a motor to only jump out and bite your new topend on the ass on its first run.

I strongly suggest just putting in new Oil Seals and a set of Fast Eddy Stainless Crank bearings. the CYs are crap, the Zens are ok, but FEs are even better. and for 13.00 for bearings. 6.00 for seals and 1 hr to install them, its a CHEAP 1hr/20.00 upgrade that your motor will love and reward you for.
 
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Totally agree and well said T. Sell the 29 back on ebay start low and get what you can. I have the non ported 27.2 noted and its a great high rev motor. I know someone with a 29 and my 27.2 will keep up with them off the start and then pass them in the high RPM's. I don't like stacking gaskets, always hear about people blowing the gaskets eventually.:glare:
Good luck.
 
Thankyou so much for all that information, it has really helped alot. I think I will get a couple of the 30.5cc kits that you gave a link to

http://www.davesmotors.com/s.nl/c.885035/n.1/it.A/id.4169/.f

as well as a couple of sets of bearings / seals. Then I can just bolt the new head on with my existing crank and 0.020in gaskets.

That sounds nice.

Cheers for all your help, I will let you know how they are running when all the work is done.

Thanks again!
 
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