mxwrench

iTrader: (1)

My point was that if the engine was running great then all of a sudden started declining and blowing plugs, then I doubt it is a squish clearance issue. But rather an engine wear issue that is contaminating the plug elements with aliminum particles causing hot spots and thus element failure.

BK

mrgsr

iTrader: (15)

I just took the engine apart and is a mess.. top of the piston looks like its been beaten with a fork and the liner has grooves in the ports

ive had so much bad luck with this engine

Corse-R

When you did this, I suppose you cleaned throrougly the combustion chamber and exchanged the old plug for a new one in order to prevent that aluminium particles contaminate the plug... (seen many people doing this and not cleaning the combustion chamber nor exchanging the glow plug).

What I suppose has happened is this. You have suffered a conjuction of events who when combined ends with a grenaded engine.

- Probably your conrod was worn and started to develop some play. This helps too to blow glow plugs.
- Doing that scoop on the combustion chamber reduced your compression ratio, so, maybe you removed 1 or 2 shims in order to regain the lost compression. This is very dangerous to do is 'as is' because in fact you're placing near two solid things and one moves at a very quick pace (the piston). If you not take some care with this, you can end with a crushed piston when everything is warm.

I did this, but removed some material too from the combustion chamber (described it on a previous post) in order to avoid a too near piston of the CC and to maintain some squish band to (the 'flat portions' on the CC aren't really flat), are made in a small angle (around 2 or 3 degrees) making some kind of small ramp.

- Tried and needed to switch to a colder plug too (sometimes going a number higher), other times needed to switch from a Hot to Cold body maintaining the same number... You're putting the plug near and receives much more heat, so you need to take this into account.

Seems easy to do, but in fact, there's much to gain doing this, but some things need to be done before to avoid detonation and grenading the internals.

BTW: An engine who blows two plugs in a row is a serious candidate for a teardown, cleaning and inspection, you never know where went metal particles of the plug wire....

mrgsr

iTrader: (15)

After the modified the head yeh i polished up the groove with fine wet sandpaper then used aluminium polish and then finally cleaned it off with fuel.

the engine was a missile in the 3 qualifiers going down the straight but the punch out of the corners was not there so were trying to tune a better low end. then we found the clutch to be not set correctly.

i gues when the first plug blew we didnt open the engine then to remove the plug wire, i guess this is what caused the second plug to blow and kill the engine

i was still using the standard shim setup under the head. when creating this scoop is it best to add or remove a shim ?

Corse-R

Milling one combustion chamber if isn't done properly, you could be doing more harm than good... needs to be perfectly squared (if not squared, something horrible could happen). The small grooves on the aluminium could lead to hot spots and detonation.

Is much better to leave the satin finish from the carbide or the HSS cutter rather than trying to mess with sandpaper. Which kind of bit you used for making the scoop?. Using diamond bits here is a no-no... much cleaner and better to use a suitable bit for aluminium.

Your lack of punch could be too due to the lesser compression (in fact, with the scoop you raised the volume on the Cc). If you plan to continue using that engine is mandatory to do a height clearance checking (use plastigauge or similar), if you have too an original (unmodified) combustion chamber a check of the volume could be great (do it with straight methanol or suitable alcohol because has much lesser surface tension and is easier to measure it rather than using water).

mrgsr

iTrader: (15)

I just used a carbide grinding tool and cut the scoop out that
im pretty sure this was all due to the tune still

what is cc ? do you mean by creating the scoop i have created more or less compression ?

Corse-R

For aluminium, sometimes is better (and cheaper too) to use an HSS bit (there are plenty of sizes, forms, etc...). Carbide for the aluminium is way overkill. Is good for cutting the steel on the crankshaft and similars.

Creating the scoop, in fact you enlarged the cavity of the Combustion Chamber, so the compression (Cranking pressure) on the engine is lowered, to regain the compresion a check of the Combustion chamber is needed to be done (check the clearance between the piston and the combustion chamber before removing any shim).

mrgsr

iTrader: (15)

i might just thro this engine in the bin
its had bad luck from the begiinng
first it blew a rod in the break in process after 7 tanks

the rod went it blew smashed the piston into the liner and killed the internals. so i have already replaced the internals and the engine is tsill new

am

Sorry, i was talking abaout your post regarding the scoop in the head button where you explain abaout lowering the head button to get back to the right compression ratio.

mrgsr

iTrader: (15)

so to put this in a simple way.. i guess by creating the scoop i created my volume.
so i should be removing a shim ?

Corse-R

In few words: Yes, but take care with the piston clearance.

am

yes, you can take away shims to get back the compression, and

no you can not just take away shims because youu get the wrong squishband. If this is to small you will get pinking, pre ignition, because clarance between piston and combustion chamber is to small tough compression is right or even to small. this is very importyant on all types of engines, not just our nitro engines.

mxwrench

iTrader: (1)

I love this thread!!

I thought I would resurect it for those people looking for info regarding the head mods. There is alot of great info about this mod here as well as some important cautions to look out for (thanks Corse R!!)

I want to give props to Dennis Ritchey for pioneering this modification for rc engines some years ago. Where have you been lately bro??

Also props to Somender Singh for enlightening us all on this simple yet effective little technique. Royalty check is in the mail!! haha

Please to all who are contemplating this modification to your own engines, take care to check your piston to head clearance (called squish) (if you are lowering your head button) and do not lower more than 0.4mm squish for .12 engines and 0.6mm squish for .21 and up, as this will definitely lead to angry parts! (or parts fighting parts, as the Japanese engineers would say)

Good luck,

BK

jfc_tech

iTrader: (4)

jag

Have you verified any gains with this head mod on the dyno?