mcx 270 nytro over boosting

[180 nytro]

hey guys i had just made a post about the mount mod seat, on the same sled it has killed a cylinder( 0 compression) due to over boosting, im in the process off pulling the engine apart and looking into it, im just trying to figure out why it overboosted in the first place?
It never overboosted until the seat was changed, and when it was changed the guy had retro fitted the stock shield to fit under the seat and had moved the little boost controller(correct me if that isnt what it is) so that it was positioned in a way that it was laying on its back with the relief vent pointing up.

so if any ideas come about, i apreciate the help.

Tim

 

[180 nytro]

ok so i have disassembled the top end and have found that one exhaust valve has kissed the piston...

there isnt any signs of damage to the piston, should i worry about changing it?

and for the valves should i change the valves for all three cylinders or just one cylinder or just the one valve that is damaged? And should the valves be upgraded for the hp output?

sorry so many questions in a short time.....

Tim

 

[kinger]

Messing with the wastegate at all will change boost levels I would be suspicous of the seat mount.

How do you know the engine failed from overboosting? Sounds like you lost a valve and that is what failed not over boosting?

I would wait for a engine guru to chime in but I would lean towards fixing the valve and assembling and go.

 

[180 nytro]

ok but nothing was done to the waste gate? unless the linkage got bent to went out of adjustment right?

and it was running fine till it started to see 22 psi then she failed, is this because of to much heat or the fact it was over reving cuz of the excess power gain?

thanks
Tim

 

[kinger]

A lot more questions can be asked from your reply:

What was the normal boost supposed to be at?

When did you see 22 psi and how long was it there?

What RPM and throttle position were you at when it failed?

Did you hit the rev limiter?

 

[180 nytro]

i believe a 270 kit should be at 15 psi.

22 psi anywhere from 3/4 to WOT, and its there as long as you hold it.

the RPM was strangley around 89-90, and correct me if im wrong but the rev limit should be 92?

and yes i could hear it hitting the rev limiter

 

[MRFUSION]

That little nipple on the tcv valve should be pointing down to let the moisture drain. The only way your boost should creep up like that is the tcv valve not working or the wastegate line pinched off. Probably something got disturbed during the install of the seat. I would out a little hand pump on the wastegate actuator and pump up about 10psi and make sure the wastegate moves smoothly. Your boost should be around 15-16 psi on the 270 kit. Good luck with your repairs. Shad

 

[180 nytro]

Ok thanks that was kinda what i was figuring that it was, just wasnt for sure, thanks very much!

Tim

 

[Dimebag]

I had my sled overboost badly a couple of times last season.
It was moisture/water in the wastegate which made it freeze up.

Check if you have a small hole on the lowest point of the wastegate.
And if not, make one.

I would also take a look at the routing of the hoses between the wastegate and the tcv. One of those hoses froze up, with the same result.

There are some pics in my garage thread if you wanna take a look.