Rb25 motor locked! Need advice

[Voltronrbz]

Yesterday, I try to crank my motor and for some reason the motor got lock after rotating 2 cycle. I then use a ratchet to rotate the pully clockwise and it  wouldn't turn, but when I rotate counterclockwise it will turn to 1 half of a cycle, and then get stuck again. So when counterclockwise is lock, clockwise rotate 1 half, then stuck again. Anyone had this happend, or might no what can be the cause of this?

[Darius]

You have a broken valve. Stop turning it. Time to take it apart.

[Voltronrbz]

Can it be a broken vale? But why that, when it was in the process of starting it back up after a headgasket swap, when before it ran fine. Last 2 days I install my timing belt onto the motor, and it rotated fine. I took off the timing belt and thought it might be the head, but still that didnt help. I was thinking maybe their was a open valve that cause the piston to hit the valve? But, I already try rotating the cams and even align the cam to mark, and still same problem.

[Darius]

It should be pretty easy to see inside the cylinders if you broke a valve and the head is sitting on the piston. Pull each plug and shine some light in there. I hope that I'm wrong on this.

If that's not it, maybe the HG is too thin and the piston is hitting the quench pad on the head? I'm stretching here.

Whatever you do, don't muscle the crank because you could gouge up the head and then you're really effed.

[placham]

Try to do what Darius said, also can you try to do a cylinder leakage test, and narrow down good cylinders from possibly bad one/s?
I'm going of a limb here that you had T-belt timing correct.

I would drain engine oil, and check for bits of metal.
Seen con rod bolts snap, one broken bolt and the cap is still held on by other, that will partially lock up the motor. Had that happen on a Celica I bought, motor was locked up. Spun rod bearing and snaped con rod bolt, bent the other bolt, and cap wedged its self between crank and block.

P.S. cylinder leakage isnt same as compression test, thought I throw that out as well just in case.

GL hope u figure it out.

[Voltronrbz]

Okay after tearing down the camshaft and cam cover, this is what I notice the different. Everything looks exactly like the housing number 1, upset housing number 2 sets different. Is this a bad valve? I took off the oil pan and see how it rotate from underneath and looks like cylinder 2 and 5 cannot rotate a full round, and 1,3,4,6 can. The picture below is from cylinder 2, exhaust side. So is this a broken valve then?

[placham]

FYI, you could do cylinder leakage test, and if you have bent/broken, worn valves, you would have air leak/escaping from what ever it would be intake valve through intake manifold, and exhaust valve through exhaust manifold. but your beyond that already.
Seems like you have a bent valve bud, notice how the two valves sit, 1 up higher than other one.
All the valve stem/spring retainer tops should be even all the way across on both sides, since you dont have cams in there isnt any pressure on them.

This is what happened to you probably

typical valve arrangement


Valve contacts piston top on a interference engine.


I would do what Darius said, and pull the head off, its a PITA, but only way to be sure. my .02 cents

[Cjmartz2k]

That last pic is AWESOME!

[robbie2883]

if the valve is broken then that spring on the right should lift right out. you'll know for sure if it's lose

[Voltronrbz]

After removing the head this is what I found.



Valve damage the piston


Now i know forsure that i will be needing a new exhaust valve. I was just carious is the piston still useable or is it trash?

[placham]

That sucks bro, I would also take head to machine shop, have valve stem bore (bronze insert) checked too, for out of round. On what ever valves were broken, and have all valves checked for leakage, they might look fin but might be slightly bent. Might as well get it magna fluxed or what every they do to check for cracks, and also for warpage/flatness.

As for the piston hard to tell, never had that happened, might want to replace it just in case, it might fail down the road.
Im sure there's a spec for pitting on piston top or something, might cause hot spots and pre-ignition/detonation, but not sure of top of my head.

[Cjmartz2k]

Trash--or at least it looks like it in the pic. If you can't sand that thing flat, it's going to create a wicked hot spot. Also, it might have done damage to the strength of the piston. Again though, depends on how deep and it's tough to tell from the pic. Sorry for your bad luck man.

[meet07]

I have 3 spare pistons if you need them.

[Voltronrbz]

This is what happend to the head. Do you guys think the head is still rebuildble also. Probably gonna change the piston, and have the machine shop check the valves.

[Voltronrbz]

I have 3 spare pistons if you need them.

How much are you asking for 1? Pm please

[placham]

Ouch, change piston, to be honkey dory on bottom end.

Take head to shop, might be okay as long as its not cracked I think, have it checked for warpage, and magna fluxed(I cant remember if part has to be steel or aluminum for this), and have all valves leak tested (might as well get them resurfaced or relaped(think thats what they call it), and have valve stem bore checked for at least that valve.

But get it checked for warpage and cracks first, cause it might be junk and no sense in throwing coin at it.

But then again I dont work in machine shop, worked on trucks now work for Union Pacific, work on their locomotives, V-16 about 12000CID of 2 stroke diesel fun

Hope you get this fixed bud.

[Cjmartz2k]

I think the head needs to be iron for magnaflux. How deep is the gouge in the head? You can usually find somebody on here selling an RB25 head for $500 or less. If worst comes to worst, I can always track down an RB25 head pretty easy. I'm already hunting up a CAS for somebody on here. Might as well grab the head it comes off LOL. Local area parts are MUCH cheaper due to shipping though, so I'd start there.

[l0nestar]

That head looks pretty haggard. I would be hesitant to rebuild the valve seat / bucket. Magnafluxing (or FPI) is a method of testing ferrous metals for surface and subsurface flaws. You could try it, but could not certify the results.

I would probably have the head tanked and blueprinted. As others have said, I would also be wary of the valve guides. What does the hone of the cylinder bore look like?

Did the valve drop into the bore when you were working on it, or was it bouncing around for some time?

[240z!!!]

i have a rb25det s1 head its missing 1 cam(or should i say its there but broken, my other head had a broken cam only bought this head to take the cam from it) looks to be in very good condition will sell for decent price text me(cory) if your interested at 615-574-4590

[Darius]

That sucks man. I did the same thing to my #6 cylinder when the pistons were up in the bore while reinstalling the head. The easiest thing to do at this point is to pick up a head and swap the old valve train into it. When you're installing the head again, put #1 at TDC then rotate the crank CCW until the 1&6 pistons drop an inch or so, then install the head and align the cams with the rear timing cover marks and then rotate the crank CW to its timing mark, and finally install the belt. That way there's no way you can eff things up.

While you have things apart, I noticed that you are installing a metal head gasket on unmachined block and head surfaces. I'd guess that you'd be pulling this apart again in the near future anyways because the gasket would have leaked. Please take the bottom end apart to get the block milled and get your new/repaired head milled. OR reinstall an OEM organic gasket. Just trying to save you heart-ache once you get things back together again and have to take things all the way apart.

[Voltronrbz]

Thanks guys for all your advice. I'm making sure this time I'm going to do everything right. I just scored a piston from eBay for 30 ship, and supposly the seller say it had good compression from all cylinder, so I'm take his word for it. I was just wondering, is 400 sound fair enough for a complete rb25 head/ no valve cover with warranty. Basically it's a 100 percent working head. I'll like to get you guys advice before I decide to buy it.

[Darius]

Probably not a bad price for a head with full valve train.

[Cjmartz2k]

Probably not a bad price for a head with full valve train.

Yup, agree.

[l0nestar]

Is that $400 shipped?

[FAST-DATSUN]

Check rod for being bent when piston hit the valve................................