Wierd problem with a friends trx 3.3?

[TK5310]

Out last night to break in my new motor & trouble shoot a mates new second hand revo.
It goes fine in the top end, but has no throttle response & no smoke at idle - winding out the LSN does nothing, it's completely unresponsive.
This has been a longish term issue, he switched his good engine to the car when he got it.
So far we've replaced all the fuel lines, the pipe, carb, air cleaner, glow plugs, fuel tank - pretty much everything bar the engine - we swapped the bits from my car to his as mine is running great so everything is known to be good.
He's sealed the engine.

It doesn't do it to start with, when he first fires it up it runs hard & is responsive off idle, but after a few minutes of run time when she gets well warmed up it starts playing up.

It's got us stumped, everything except the engine has been changed out & the engine has been sealed, got NFI why it's behaving like this - only thought is he must have messed up on sealing it somewhere, or the block is cracked somewhere, a fairly big air leak that only opens up as the motor warms up is the only thing I can think of unless you guys have any other suggestions?

 

[bgbdwlf2500]

Sounds like once its hot ur losing compression. Time for new piston and sleeve

 

[TK5310]

Could be I guess, but the motor is only a gallon or so old.

We'll switch it with a spare engine, if the spare is good in the car then we'll look closer at the 'good' engine.

 

[Grave]

the engine might be getting too hot & robbing you in performance what kinda engine temps are you running

 

[REVO-5309]

i had problems exactly the same as this with my idle when my motor karked it. the crank had massive wear marks in it as the front bearing let go and the compression was getting low. but i had 8-12 gallons through mine. i replaced the rear bearing but not the front as it seemed fine at the 4-5gallon mark. i guess i should of changed it, would of lasted longer. but it started straight off the bat and went hard till it was warm. once warmed up the LSN didnt seem to do much. wouldnt wheelie anymore and top end was still fine. where as before it was warmed up it would wheelie easy etc.

in saying this might be a good idea to pull the motor down, check the bearings, crank, rod, piston/sleeve and seal everything. check the tank, header, exhaust and lines for air leaks.

temp might be a problem too but wouldnt be a bad idea to pull the motor down and double check it.

 

[TK5310]

Rebuilt with spare block, bearings & crank, everything else went back in - fixed.
Doesn't appear to be anything wrong with the old block etc, but there is an issue there somewhere.

Meh, it works now, 3 hours of skate park fun last night & it didn't miss a beat.

 

[REVO-5309]

old vs new, lol....

---------- Post added at 10:00 AM ---------- Previous post was at 9:59 AM ----------

 

[TK5310]

Yeah, ah, thats kinda dead!

His was nothing like that, it all looks pretty good actually.
It was probably just an air leak that got worse as the metal heated up & expanded, but we'll never know, it's fixed now!