Rb25 blown?

[Prof_Finesser]

Hello again I just got my rb25 tuned yesterday made 450 forged internals and semi built head I went on a beer run and let the car warm up before I got on it and I did a small pull and then about a minute later the engine shut off. I towed it back to the house and been tearing into it today. It’s odd I cant turn the engine by hand to the right (intake to exhaust side) it has some wiggle then it stops and won’t turn any more but I can turn it to the left no problem. I did a leak down and all cylinders were in good condition. I’m so lost at this point. I checked cams in case they snapped and they are all good too. I think I’m going to pull the head off tomorrow just to see what’s going on because I don’t understand.

[GTSBoy]

Well, it's too weird to be making any guesses. I'd have the plugs out and a borescope into the cylinders before doing anything else.

When you say

51 minutes ago, Prof_Finesser said:

I can turn it to the left no problem

Do you mean to say that you can turn it over continuously? Like, it's not seized or blocked from rotation outright? Only won't turn forwards? If so, would sound perhaps like something has dropped into the timing belt area or has otherwise arranged itself like a ratchet pawl, so that it prevents rotation one way, but not the other.

[Prof_Finesser]

3 minutes ago, GTSBoy said:

Well, it's too weird to be making any guesses. I'd have the plugs out and a borescope into the cylinders before doing anything else.

When you say

Do you mean to say that you can turn it over continuously? Like, it's not seized or blocked from rotation outright? Only won't turn forwards? If so, would sound perhaps like something has dropped into the timing belt area or has otherwise arranged itself like a ratchet pawl, so that it prevents rotation one way, but not the other.

Yes and that’s what I think as well and yes the rotation is continuous 

[Prof_Finesser]

I just got back from the parts store and got a bore scope as well gonna check them out 

[Prof_Finesser]

Even with the starter it wouldn’t turn because when it first died I thought it was just a fling and tried starting it 

[Dose Pipe Sutututu]

sounds like something something has made love.

[Prof_Finesser]

43 minutes ago, Dose Pipe Sutututu said:

sounds like something something has made love.

I think ur right cylinder 2 has some valve looking marks on the bore scope 

[Prof_Finesser]

Wont it not hold pressure during leak down though?

Edited August 26, 2024 by Prof_Finesser

[Dose Pipe Sutututu]

Most likely won't hold pressure, however it is still possible if the valve isn't bent

[Prof_Finesser]

3 minutes ago, Dose Pipe Sutututu said:

Most likely won't hold pressure, however it is still possible if the valve isn't bent

I just realized something I’m at TDC and my intake cam is at the timing mark the horizontal mark and my exhaust cam is at like 7-8 o’clock position not even close to the timing mark. I’ve timed these engines about 5 times now and always do it the same line up the 3 marks crank and two cam. How tf have my cam spun that far off. I’m gonna check all the timing system tomorrow 

[MBS206]

3 hours ago, Prof_Finesser said:

I just realized something I’m at TDC and my intake cam is at the timing mark the horizontal mark and my exhaust cam is at like 7-8 o’clock position not even close to the timing mark. I’ve timed these engines about 5 times now and always do it the same line up the 3 marks crank and two cam. How tf have my cam spun that far off. I’m gonna check all the timing system tomorrow 

Many possibilities, like cam gears coming free of the cam shaft and spinning.

[Dose Pipe Sutututu]

Or camshaft snapped (has happened to me)

[Prof_Finesser]

22 minutes ago, MBS206 said:

Many possibilities, like cam gears coming free of the cam shaft and spinning.

Yea ima just take the head off tomorrow 

[Prof_Finesser]

2 minutes ago, Dose Pipe Sutututu said:

Or camshaft snapped (has happened to me)

That was the first thing I checked lol thought it happened to me 

[Dose Pipe Sutututu]

12 minutes ago, Prof_Finesser said:

Yea ima just take the head off tomorrow 

best way to diagnose to be honest

[Prof_Finesser]

Just now, Dose Pipe Sutututu said:

best way to diagnose to be honest

Yea I’ll let u know what happens hoping that I can still use my pistons and just rebuild the head 

[Prof_Finesser]

So good news and bad head is off. Good news engine is turning again forwards continuously and pistons have very small mark on the top where valves hit it does catch a finger nail going to still ask machinist if it’s ok to run I think they will be ok.  On to the bad I took the exhaust cam off because the exhaust valves where the only on the pistons and it seems like my first cam cap (closest to timing gear) was eating into the camshaft and end up stopping it all the valves have the marks in picture. 
 

[Prof_Finesser]

Combustion chambers look to be in good condition as well 

[Prof_Finesser]

Dropped off head at machine shop he told me probably going to need valves and a new head core.  If anyone has a RB25de non vct head please let me know.

[Murray_Calavera]

Did the machinist give any indication as to why the head failed the way it did?