duckedup

I have a SH P6-28 ProSpec (basically a LRP Spec2) and I've been running an OS#8 plugs in it so far.. I run 20% Blue Thunder for now (1/4 gallon left) and I'll be switching to 30% when it's gone.. The climate here is cool (50's give or take) and will be for the next 6 months or so..

1st Q is: I have a few Traxxas plugs left over from the Jato I had, still new.. they are #3231 (long/medium) can I use these in this motor? I noticed they fit but they're a little longer so I wasn't sure if that would bump up the compression too much...

2nd Q: I recently read that the McCoy MC8 or 9 are a better plug for these engines, is that true?.. I read that the reason they are better is because they're longer (which might answer my 1st question, I just want to make sure..)

3rd Q: When I switch to 30%, will I need to add a head shim?

Thanks for any help!

mozzzy_2000

hey hows it going? I know there is a traxxas plug called heavy duty medium thats basically a rebranded Mccoy 8. I think these maybe what you have left over? You are correct, the Mccoys are longer than the OS plugs and yes in some engines this will cause over compression. But if they recommend the mccoys for the SH I would stick with those. I have a few italian engines and they all run on the long shafts. They simply don;t like the shorter OS plugs so I am guessing your engine is the same. In this case the OS plugs don;t offer the right compression which will cause all sorts of tuning woes. Same as if you use the mccoys on an engine that use os plugs. Over compressing will also give you trouble. They may not look that much longer/shorter but it only takes a few mm to change the compression. Also when Mccoy plugs are scarce where I live here in Oz, I use an OS8 WITHOUT the washer. This effectively makes it a long shaft. If doing this, just makes sure its nipped up nice and tight.
If you are switching from 20% to 30% nitro I would definately add a shim. What size shim? not sure to be honest but the manual should tell you hopefully but generally most engines are good for upto about 25% before you need to add a shim to reduce compression.
Also going from 20% to 30% is quite a jump to change. Ordinarily purests will tell you that going up in nitro % is not advisable but I have done it successfully with quite a few engines. The only thing you need to do is basically re-run it in. I can hear you "sigh" but yes it needs to be done since yoy have run the engine in on 20%, the tolerances will be different than that of running 30% so you need to run it in gently. Like a sort of mini run in if you like. Heat cycle a few tanks in gently without pushing the car too much and you should be fine.
But you will need to shim the head. Your LHS would be able to advise as to what shim to use but I think they will either be .1 or .2 mm shims.
Hope this helps?
Cheers
Matt

duckedup

thanks for the response...

yes, the plugs I have are the heavy duty ones.. so that's good news (the re-badged McCoy part)

I've noticed that this motor seems to lose a little performance/punch after it's gets to normal operating temps, it's got tons of power up to that point though, it'll wheelie and I can flip it on it's lid hard with heavy tires and 18/48 gearing (stock is 16/52) up until it get's to normal temps that is... I've also noticed that when I go to restart it (after it's warm) it doesn't have nearly as much pinch.. might be the short plug..?.. Not really sure though, seems to have plenty of compression when it's cold.. my friends Nemesis still has plenty of compression in comparison when it's warm[sm=confused.gif]

also.. I've always heard that going up in nitro % is ok but switching back-n-forth is bad, you just have to stick to the new % from there on.. if I have to re-break it in again, that's no big deal, that's how I broke it in to start and it's a lot less headache than the manufactures rich->lean method.. I'll do that just to be safe, definitely couldn't hurt anything..

One other question that I had which I fogot to mention... My OWB drags and that's gotta' be causing a lot of resistance at higher RPM's.. I've lightly oiled it with vegetable oil and that helped a little but it still drags.. any ideas on a fix..?.. I didn't have that problem with the motors I've had in the past.. I 1st noticed this during break-in, I had to hold the flywheel in place in order to keep the piston at BDC (when the pull start cord retracts) when cooling the engine.

thanks again..

mozzzy_2000

Sorry dude I don;t quite follow you. What does OWB stand for?

Also when you say its loosing compression, whats happening exactly? Are you noticing a drop in power after a few tanks? Most engines will lose that pinch when warm. Its what they are designed to do since its a ringless piston. The tapered sleeve expands under normal operating temps.

I am thinking you maybe getting it confused with the clutch slipping perhaps? This is quite common after a few tanks as the clutch gets too hot. This will result in sluggish performance. Could there a link in the presuure line? What sort of temp is the engine running?

duckedup

OWB = One Way Bearing (for the pull start).. It drags, catches in the direction it's not supposed to.. seems like that would rob from the top end RPM's & power.. I'm wondering if there's a better lube other than vegetable oil or if that'll even help..

As far as losing power.. It could be the clutch, I just replaced the Nova shoes and they were pretty worn.. I know that the motors are supposed to lose compression after they're warm, mine just seems to lose a lot more than my friends motor after it's warm.. totally different engines though (about the same amount of fuel through both, less than a gallon).... I'm going to go ahead and put a longer plug in and give it a shot..

engine temps are no more than 240.. Idles good, holds a tune, lots of power at 1st.. we'll see how the new plugs work out.. The shoes and the longer plug might be the fixes for the topic.. not sure about the OWB though

mozzzy_2000

oh ok yeah the OWB I don;t know too much about to be honest. all my engines are starter box engines but I have heard of these OWB getting gummed up & sticking. this may very well be your problem.

Yeah I'd try a longer plug. Like the Mccoys or O'donnells. Top quality plugs. Plug temp maybe a factor too. What plugs are you using & what fuel %?

mozzzy_2000

sorry mate I forgot that I already asked you the questions above. Yeah I'd try the Mccoys definately. Have you made the switch to 30% yet? I'd try a Mccoy#8 if its quite cool there going into winter. If it gets humid or wet, you want to use an even hotter plug, perhaps the Mc59. Once you hit 30% though, you'll probably need to run the colder Mc9.

duckedup

I've still gotta run what I have left of my 20% (about a liter) and the weather isn't too great so it might be a little bit before I get to run.. It is cold here for the next 6 months or so, fairly humid too.. I'll try the new plugs and go from there... thanks for the help

mozzzy_2000

yeah I'd try the Mc59 as its great when its cold or humid.

supertib

okay DO NOT ADD HEAD SHIMS , the motor comes with an .024 clearance from factory, it is meant to run 30% right off the bat.... with 20% your not seeing what it can do as its shimmed for 30% right from factory....

and use an MC-8 or OS-8...... the motor will want to overheat with 20%, and wont make full power once its broken in, the motor needs 30%....

duckedup

right on, that's good to hear![sm=thumbup.gif].... after reading that, I might just give the rest of the fuel I have left to my buddy and go get some of the good stuff[>:].....

Thanks for the help guys!