Engine build and dismantle ideas

Hi All,

Some thoughts on building and dismantling Cox engines or any engine for that matter. I understand many of the methods and ideas on the forum are proven methods used and deloped against old, forgotten, and often abused engines, hence the need for methods such as heat and or my favorite which I havent seen mentioned so much "brute force and ignorance". Lol.

My ideas and suggestions come from racing two stroke yamaha TZ grand prix bikes. Where we had safety issues as well as the need to regularly do partial rebuilds. Piston rings every race meeting, pistons about every 3 race meetings and crankshaft rebuilds every 500 miles including practice miles. We worked with many different metals from chrome or nikasil lined barrels, Titanium con-rods, and many bolts were titanium, as well as the cast " Hiroshima wonder metal", and chrome molly.

Starting with new parts and maintaining them is a very different situation to that many in this forum find themselves in, but here are some things I learned from another sport where the parts and engines were generally new and less abused. Lol. Some of the ideas I got direct from the Japanese factory engine mechanics when asked to help out by doing laps on their bikes to test tires.

No Silicon. No Silicon near engines. Straight silicon tends to form into little balls inside your engine when used on various parts for various reasons, and those little balls always find a hole to block, generally an oil gallery or such. Blown crank or gearbox, etc... not so bad on a cox motor, less little holes to block. I have seen it suggested to use silicon to seal barrels all kinds of things. There are better ways I believe. Some products have silicon in them but have other chemicals in them and dont behave in this way. I tended to use permatex non hardening aviation gasket liquid sealant and yamabond to seal things up. Preferably perfect surfaces and new gaskets, and sometimes still a bit of permatex which meant definitely new gasket each time. But NO pure silicon

Bolts, studs, screws, nuts etc, all were dipped in the wonder oil 'trans fluid' before assembly and probably tightening with a torque wrench. The oil stopped the bolts etc. seizing up inside the dissimilar metals and seemed to do wonders for preserving threads that were being constantly undone and done up. Trans fluid was also used for storing parts. clean the part, wipe over with trans fluid, wrap in a rag, and its still good years later. No WD40. WD40 is nasty stuff, use when you must, but clean completely off after. As a side note, we used trans fluid in our straight cut six speed manual gearboxes, it handled heat and pressure better, got in everywhere, didnt foam up, less resistance to the gears turning, so better speed and came out cleaner, which tells its own story. We ran dry clutches so that wasnt an issue in doing it.

Lock-wire. fantastic method. stops things undoing, coming loose and falling off, like you gearbox drain undoing during a race or your break caliper bolts coming loose etc. it was checked heavily in scrutineering where they checked certain items were lock-wired.

I have read in forum topics where people have had issues with things like cylinders, heads,.... coming loose. lock-wire them with really really thin lockwire. you need to be able to drill two very small holes close together if possible and on different parts and then lock-wire them together. Permatex non hardening aviation gasket liquid sealant used very sparingly will stop a cylinder rotating but will dismantle without heat.

JB-Weld can be a great product it seems very similar to a Yamaha product we used to use mostly when very heavily modifying barrels. I cant remember its name now, but it was like aluminum in a paste that was mixed with other stuff and wonders could be performed. We could machine off the cast metal inlets that held the carbys and build brand new new really big inlets by machining it when it was set. we also went to the extend where we wanted transfer ports that would be wider than the barrel so we could use this stuff and then machine it as part of the barrel once it was set. I assume it is much like JB weld which I have not yet used. One really serious problem we found with this stuff was that if it wasnt mixed, set and cured to perfection in the correct conditions, nice dry non humid days, it could look perfect, machine perfect, and seem to run perfect, untill you got up into very high sustained revs say down a long straight and it would start sucking air and you would blow an engine to pieces. The stuff might be a bit porous but only when the pressures were high was it noticeable. This was not the standard result of using the stuff, but it certainly happened to some unlucky teams.

So to me and my ways. new or newish engine. Pull apart, inspect, clean every part, cleaning is when you find little things you otherwise miss. thats why I cleaned my race bike. clean the part, check the lock-wire, check the bolt, nut is done up. cleaning is great for reliability! use lock-wire on things that might come loose or tend to spin, this is better than doing them up super tight, which just stretches the thread and next time you need to do even more super tight..... Lock-wire or use a lightweight sealant as suggested above, stops spinning, stops air leaks. use trans fluid on threads, pull apart and clean thoroughly now and then, and then re-assemble. Use new gaskets!!!! yes, use new gaskets or just dont bother pulling apart and cleaning. Lol. get the leftover fuel out of your engine, tank and lines at the end of the day. Its not nice stuff for anything but burning in a combustion chamber. Run your engine as recommended by the manufacturer and it will be reliable and do what you want. If your going to mod an engine, dont be half hearted, your already outside of recommended specs for reliable known running, so build a bloody hand-grenade motor you can be really proud of Lol. :-)

My rambling personal thoughts that may be utter rubbish.
If they help you out at all that is great, if not, no harm done. :-)

Take it easy.
Cheers,
Gary

Whilst your ideas are all valid-I think you may have overlooked the issue of scale here....things like lockwires may work very well on a 10mm bolt....but when you're dealing with a 2-56 screw for example-cross drilling for a lockwire becomes a nonsense-let alone finding castellated nuts in our sizes!....and in the Cox engine range we are dealing with that sort of size for assembly screws. Some form of antiseize compound may be appropriate in some uses, thread lockers in others. mountings and propeller balance tend to be overlooked as sources of vibration-and a good amount of attention paid to these two aspects yield dividends. that and using the correct tools correctly....FWIW I use metal bearers on my larger FF models-as do many control line racing type designs such as team race and rat race class models-and of course CL speed models use full length metal pans-but that sort of thing is not really practical in the 1/2A engine and smaller regimes

ChrisM
'ffkiwi'