Rebuilt motor, 100/150/150/150 comp ratio after short idle...

[babowc]

So I turned the key on my setup and she started up perfect and was able to idle for a good while and I shut it off last night.

Today I go out to turn it on to break it in and whaddaya know, it doesn't start. it's got fuel and spark too!

So I took the time to do a comp test and 1st cylinder was 100 and everything else was 150-160, so I took off the head and this is what I found.

I have CP pistons, BC SS valves, BC springs and BC 264 cams.My timing was good when I assembled the motor.When I took the front cover off, I could see that the damn thing jumped timing somehow.

Anyways.. this is the aftermath.. I don't even know how the head got scored on the intake valve sides.. I know I'm not gonna be able to reuse the head, but can anyone explain to me what I did wrong or what went wrong?

BTW, I was using cometic gasket too.. I already bought a felpro.And would I be able to use the pistons again?

I also took the head off to check what was up with the valves and it seems the first cylinder's lack of compression may have been due to an intake valve that didn't seat completely. I'm guessing this happened after it made contact with my pistons because the compression ratios were all 150-160 the first time I checked it on the rebuilt motor.

One more question!what does "Oversize head diameter only" mean? I just checked BC website and that's what it said for their SS valves.

[KFL]

Was headwork done? if not it should have, oversized valves are just that slightly bigger than oem. For the ka24de its .5mm bigger, checked bc website. So, it needs to be enlarged to accomodate the bigger size so it seats fully. The damage on the pistons looks to be about .5mm.

Only things that could cause that damage timing chain broke, cam gear loose on intake side, inproper valve/piston clearances.I'm not sure if those pistons are resuable, but I would say probably not. Valves are bent most likely.. Hopefully more will chime in with more info.

[babowc]

They all seem to seat completely fine with cylinder 1 being the exception.

I'm tearing the head apart tomorrow to see what happened and if the valves are bent or not.

We'll see.. if anyone else has had similiar problems or have any valuable input, feel free to chime.

[nelson8708]

I would take a dremel or some thing and lightly sand down the spots where the valves hit the pistons so there are no sharp edges, but i would re-use them. The sharp edges could cause detonation. Put the valves in a drill (lightly tighten the chuck) and spin them to check to see if they are all bent.

This thread makes me

[babowc]

gooooood idea on the bent checking procedure. I need to go get one of those valve remover tools.

[480sx]

Idk man im lead to believe that it was something wrong with your cam timing, because oversized valves arnt going to be the cause of piston to valve contact. I would take the head to the machinist and ask him wtf happened.

Ka's dont just jump timing unless your chain breaks. Did you spin the motor 5-10 times over before you started it without the plugs in to make sure everything felt good? I ALWAYS do this on interference motors, even when im dead sure that i got the timing right. Cuz everyone makes mistakes, and you never know.

Sorry dude, that sucks.

[PorkChopExpress]

give ya $15 a piece for those ash trays.

heheh im such a scum bag.

[babowc]

Yeah.. it does suck.I'm reusing the pistons though.. like a few people suggested.

As far as the valves go.. I saw some cracking along the intake valves.. I'll see what that's about.

[spank044]

I had this happen when I tried to get too much timing out of my intake cam with the first 248/248 cam swap. It cost me $250 to get my valve seats re-cut and some guides replaced. The pistons are reusable, but I would gently clean them up with a scotch pad. If just the intake valves hit then your timing was off. Is the bore stock? If this problem continues then you need to get pistons with valve recesses.

[babowc]

I see...

Well, I did tear it down today and found these:Aftermath:





Intake valves were cracked and distorted.the shaft was good but the valve area was warped.bore is .020 over and the exhaust valves are still good.i'm going to just stick a stock head on there and get another set of intake valves when I get some more cash..

thanks for your input spank044. My timing seemed to have been off when I took the cover off.I swear I had the timing right when I put it together though.. what could cause it to jump timing?

[480sx]

If you had operational tensioners both top and bottom, and oil pressure, there is no physical way that it can jump timing(ignore AMS's drag 240[Shimmed oil pump ftl and an over rev on that one IMO]) if the chain and guides stay intact. Even if the bottom guide breaks, its still not gona jump just make a bad noise.

The only way this happened is that you had your cam timing off a tooth from the start. This was most likely caused by one of two situations, unless you did something just outright wrong like.. Idk didnt have TDC set or didnt line the dots up.

A - When you lined up the dot on the crank sprocket then put the lower cover on + the middle sprocket, you let it move a tooth. This happened to me but i realized it moved when it happened and just had to pull the cover again. Its not hard to make this mistake.

B - When you installed the idler sprocket, then the upper timing gear, you let the bottom of the top chain skip a tooth. This is less likely simply because you said you had it set right to begin with, and im assuming that you know what a Ka's cams at TDC looks like, 10 and 2 right? At TDC, the intake and the exhaust cams sit at the same exact angle away from each other, upwards.

[babowc]

Yep, I know exactly what it looks like because I had it wrong the first time and someone corrected me on here.

Well.. I'm getting a different tool than the generic compressor tool.my hands hurt like s*** from squeezing the tool.

You can be sure I'm gonna check and double check and triple check the cam timing before I start the car this time around.

[nelson8708]

I wouldn't bother removing the pistons. Just spin each one to tdc and clean it up. Hopefully engine #2 has a better beginning

[Daily Driven 240]

480sx im just curious why you mentioned that the AMS drag 240sx shimmed oil pump was FTL?? sorry about the off topic but im planing on shimming mine so im curious.

[480sx]

AMS's drag 240 had an engine fail because the tensioner actually blew out of its 'cylinder'. They dont really advertise it, but this is most likely a result of their shimmed oil pump(along with the fact it was a high hp drag motor that was probably pushed to its absolute limits all the time heh). Along with maybe an over rev and almost for sure, the extra oil pressure.

For your normal build its probably fine, i have a bunch of shims i punched out that are perfect for +5-7 psi and ill probably run one, havnt made up my mind yet.

[babowc]

Got a new head, surfaced and hottanked. added new valve seals and used stock components with bc264 cams.btw, I just reused the pistons and burred down the sharp parts a little bit with a wirewheel and dremel.came out looking mighty nice. after I wirewheeled the pistons.

I just put everything back in and lined everything up again.. just need to complete it by adding stock ex. mani and hopefully she'll be good.

[480sx]

GL man. Rotate your engine without the plugs in a few times, make sure you have your cam timing right.