New picco .28 monster build!

[Extreme RC Mods]

I would do a pinch test, take the glow plug out and use the flywheel to spin the engine over and see how tight it is at TDC. I'm only mentioning this because the revo doesn't take much to push but if the engine is still tight it is very hard on it to run it too hard too soon. I would recommend taking it easy for at least the first gallon even if it's not very tight. The piston and sleeve have to match to each other, if they are tight then that's good and perfectly normal. If the fitment is not very tight then you want to take it really easy and let whatever pinch you have and let it match slowly, that way it will have a better chance of making a good seal and mainly wear the tight/high spots. Running it too hard will wear everything including the low spots and could potentially shorten the life expectancy quite a bit. I'm not sure the state of your engine but gave a detailed answer anyways lol

 

[TK5310]

It's tight, real tight!

Like, warm it up with a heat gun, rip the plug out & struggle to turn it over by hand tight.

Bump start just peels off rubber or stalls trying to turn it over a lot of the time.

Mofo is TIGHT!

I'm running it pig rich & not revving it hard, but have been giving it WOT - it's geared for a moon shot, no need to wind it out for some pretty high speed!

 

[REVO-5309]

mine LRP 28 is still tight, I'm around 1/2 gallon now and turning it by hand with pull start while warm still gets tight and sometimes stuck if not pulled hard enough.

 

[TK5310]

The trials & tribulations of teething issues on a scratch built big block revo LOL:

Sheared driveshaft pins - made tool steel pins, all good now
Stripped plastic spur gear - turns out it was a 42 tooth, replaced with a 40t & spun up a new billet alloy adaptor for the revo trans, 40t is small enough that I could ditch the trans spacers & still have enough room to set the lash.
Smashed 1st gear - replaced with a second hand one I had & loosened the slipper clutch, will put a RR metal 1st gear in it soonish.
Throttle linkage & servo were crap, always sticking, rarely getting full throttle & not returning to idle properly. Cracked the sh|ts with it & made a new one with a steel riser post, billet alloy arm, roller bearing pivot & rose jointed link to the servo, replaced the servo with a digital PowerHD high torque one. Throttle & brake control are now outstanding, much, much better than an analouge servo, just gotta be carefull with the brake, there is enough braking power to front flip the thing under brakes at high speed if the tyres grab rather than slide.
I managed to put the clutch in backwards whilst sorting the new metal spur & adaptor plate, destroyed the clutch & overheated the bell gear before I figured out what was going on, replaced the clutch with a HoBao 3 arm alloy.
Centre diff is now non-functional, blutack has gone walkabout, gotta pull the trans down & cram the diff full of bluetack again & seal it up to stop it squeezing out.
Centre diff being way too loose has blown both front tyres off the rims - just need to be re-glued.
Header tank has been causing some wierd tuning issues, she'll be running strong, I just get the tune right & all of a sudden she'll go pig rich out of the blue - I pissed off the header tank & she's much more stable, wierd, should be other way round, but it is what it is.
& lastly - stripped the metal bell gear, never heard of that before, best I can figure the clutch being in backwards overheated the bell gear to the point that the heat treating gave up & the metal got soft, dunno, but she's stripped good & proper! Lotsa sparks & grinding noises, hardened steel spur survived just fine tho - which is good, coz that was bloody expensive!

So, almost through the issues, when she's been running well it's a goddam weapon, motor still needs to be warmed up to start but has a gallon on it now & is freeing up & making more power every time I take it out, it's almost uncontrollable on full throttle.

Have to pull the truck down & sort a few things now I've actually had some time running it:

Replace clutch bell
Refill centre diff with blutack & seal
Thicker oil for front diff, thinner oil for rear diff
Soften up the rear suspension so it squats a bit rather than lifting the front so easy & ballooning the tyres.
Replace 1st gear with a RR steel setup.

 

[TK5310]

Oh yeah - had it out at a skate park last night that has a huge bowl, had it belting around the vertical part of the bowl at high speed, just doing laps with the car running round & round on the vertical wall.
Then came the kodak moment - wheestand whilst on the vertical wall, awesome!

 

[sv250]

Post some pics of the linkage please. I'm building a LRP Revo and tahts the problem I'm running into.

 

[REVO-5309]

Try change ur gearing. I'm running 36/17 and it's good fun. I have clutch problems with mine ATM tho

 

[TK5310]

I'm running 20/40 gearing, which is actually taller than your 17/36 & with the big joe tyres it gets even taller. The picco pulls that gearing no problem, will still wheelstand in 2nd gear at stupid speeds (well, it does when the centre diff is locked up a bit better than it is now).
I'm running 1/8 buggy/truggy type clutch bell & spur - much bigger clutch than TRX, now I've got the alloy arms in there I can't forsee any problems with it in the future.

Post some pics of the linkage please. I'm building a LRP Revo and tahts the problem I'm running into.

I'll take a pic or 2 in the next couple of days & post it up, but it probably won't help you - I made it on my lathe.
Best thing you can do is grab a high torque digital servo, the stock one doesn't have enough travel (or torque), even a 2075 is short on travel for the longer movement of a big block carb slide.

 

[TK5310]

Out last night, destroyed another 1st gear, got a close ratio set in it now, all I had left - need metal 1st gear real soon LOL.
Raped the centre diff again, even packed full of blutack it lasts about 15 minutes before it's an open centre again.
I give up on it, it's just not designed to work with this much power.
I can't put a FOC back in tho, my rear shaft is too short with the shorter FOC shaft & I can't use the rear brake with a FOC (the extra braking power is good, even without the centre diff), so I'm just gonna fill the centre diff with epoxy to lock it up.

Other than that I got about 6-7 tanks of fuel through it, motor is really starting to come alive, still needs to be warmed up to start, but once she's up to temp its just plain crazy.

 

[beave]

would you happen to know what brand the motor mount is? i am having issues with lower block clearance on my revo. trying to put an os speed .21 in it. the mount i have had to be ground away some and i am not happy with how much material i had to remove, thanks

 

[jk6672]

Nice mil. I have the same in a Revo with the new era block. I didn't use their linkage though, I used a generic Ofna linkage and it worked perfect.

 

[TK5310]

Had this out again last night, it's running real strong now, stupid fast!

I gave up on the centre diff & filled it with epoxy to lock it - much better, just gotta be carefull with the throttle or she'll backflip or stand up on the wing. It managed a full backflip to land back on it's wheels last night.
It's not trying to tear the front tyres apart any more & is actually quicker by a fair margin - just not as forgiving on a heavy throttle finger.

I stripped another bell gear - thats 2x hardened bell gears torn apart now, so there is obviously an issue with the chassis flexing under power, mesh was spot on but it tore the tops off the teeth.
The hardened metal spur gear is still fine.

So I've got to pull the car down & weld in some extra bracing in the engine bay area to stop it flexing - bell gears should not be a consumable item!

I've got a full metal RR wide ratio gear set coming & will put in metal driveshafts soon as well - should be getting close to bulletproof then.

 

[Snook Man]

What clutch bell are you using? If its not a hardened steel bell the steel spur will eat it.
I've run plenty of BB engines in a revo with a stock plastic spur and never stripped one due to chassis flex.

 

[beave]

check and see if the inside of the engine where it meets the block isn't hitting the bottom of the engine. look from the rear suspension with a flash light,also check to see if the block is hitting the chassis on the inside rear point,i had this issue....

 

[TK5310]

I'm just using HoBao 20t buggy clutch bells.

I've got a QConcepts engine mount - it gets the motor real low so I can use a bump start no probs, but doesn't seem very rigid & I can't use the stock TRX chassis brace - just the bare chassis.

Mount fits the motor perfectly - after a little work with a needle file!
No probs there.

Maybe the clutch bells just aren't hard enough - that would sort of make sense as the spur gear is real hard & has just chewed up the bell without suffering any damage whatsoever.

But - some of the teeth on the bell are sheared off closer to the tip, indicating that the mesh was not deep enough even though the mesh was near as dammit to perfect.
Other teeth were chewed down flush - but that would have happened after the initial tooth failure.
That sort of indicates that the front of the motor has been flexing down under power (the design of that sort of gear means they will try to push apart under load, the more load you feed through them the harder they'll push apart).
I suspect under power the gears are pushing apart & the chassis is not rigid enough to resist the movement, so the front of the engine pushes down, the mesh gets a lot looser & the tips of the teeth get chewed off, then it just chews the rest to bits.

I'll try to drill the clutch bell with a boron drill - boron drill wouldn't touch the spur, so if it drills the bell it's a safe bet the bell is too soft.

Could also be a combination of both - soft bell material & chassis flex.

If the bell is soft I'll find a properly case hardened one first - much easier than stripping the whole car down to tig weld reinforcement onto the chassis.

 

[beave]

by chassis brace do you mean the aluminum "u" shaped piece? as long as the cradle is bolted to the mount bars it should be secure,what b.b. mount do you have? Qconcepts,not sure i've heard of them,have to try and find it and see what they look like...found the mount,i like the way it looks,trying to get one...

 

[TK5310]

Turns out the clutch bells I were using were just soft, put a hardened 17t bell in a mate had & it's sweet.

It turns out the carb had the smallest venturi in it which was limiting top end power, I popped it in the lathe & drilled it out to the carb throat size (9mm), big difference! Easier to tune & heaps more top end.
Motor has 1.5 gallons on it now & is really coming alive, with the 17t bell in it's difficult to keep the front down, she'll pull the front up in top gear & backflip from a standing start.
I ditched the locked centre diff & put the FOC back in, had to lengthen the rear drive shaft.

Smashed a diff now tho, destroyed the carrier.

Got 2x steel diff cups coming, RR full metal wide ratio gear set, steel 1/2 shafts & will be switching to a savage slipper instead of using the revo slipper with an adaptor plate for the 'normal' tooth profile spur gear.

If the savage slipper works out well I'll post some pics - using 1/8 clutch bells allows the use of the bigger 1/8 clutches, so no issues with the revo size clutches not coping with the power.

When that lot is done there will not be a single plastic driveline component left.

 

[TK5310]

This is in the middle of the next round of upgrades, I've fitted steel 1/2 shafts front & rear, billet alloy diff cups & new rear diff (was smashing rear diffs a bit too regular).
Made a roller bearing billet alloy throttle linkage with rose joints & a steel riser post.
Made & fitted a TIG welded chromemoly tube roll bar that sits about 1/2" higher than the stock plastic bar to protect the engine better.
My RR steel wide ratio gear set just arrived & I've got a new 4 shoe progressive alloy clutch & new flywheel to go on as well.
Waiting on a 38t RR slipper conversion - maybe tomorow.

As she sits now after a bit of a clean up:

 

[joshman1204]

Looks like it is coming along nicely!

What would you charge me to make one of those bars and ship it to the states?

 

[TK5310]

LOL, would end up costing you a fortune!
Freight alone would be something like $40 & machine shop time is $100 an hour (I own the shop tho, so I don't charge myself much).

You can buy a very similar bar, can't remember the name tho - I just didn't feel like waiting 2-3 weeks to get one shipped over & I had some left over cromo tube laying around.