having a few problems with my high compression KA

[driftaholic]

dohc with sohc pistons, 2 exhaust cams, no egr, and no aiv. octane is sufficient.

problem #1: can't get timing down.the best i could only get was 15º btdc, so i pulled the distributor out and rotated it one tooth, and then the best i could get was 30º advanced. coldn't get to 22-18º btdc, so now i'm just running at 15º.

problem #2: won't idle.sometimes idled around 1000rpm when my timing was 80º retarded, but now it won't idle at all. it bounces between 300 and 400 rpm, then dies. i have to heel-toe when coming to a stoplight to keep the motor alive. adjusting timing didn't help this too much. last night when i came home it stalled, smoked, and wouldn't start again.

problem #3: ticking.varies with rpm, and it's not the timing chain. i took both guides off and the chain is in good condition. closed throttle: no tickingpartially open, but not enough to accellerate: tickingaccellerating: no ticking.

checked my compression last night and it's 185-240-85-245. plug #4 had wet oil on it.

i'm also leaking oil, so i'll have to see where that's coming from.

so, who wants to take a crack at it?

[Thee 240sx Owner]

# 1... are your cams timed right? is everything phsically timed right? #2 Your compession is really off on some of those cylinders.. did you send the block and pistons to be re miled? i'm thinking that the pistons are worn out of circle and that the block isn't the same roundness as those pistons are... even new piston rings wouldn't fix the problem which probably is the reasons why your leaking oil and also explains probably why your ticking... most likely its the piston head slapping around from be out of roundness in a cylinder chamber that isn't worn to that cylinder.... i would check all that before hand... now as for timing i'm thinking its from the compression not being even and the motor won't idle right cuz the computer is continually adjusting for the different in the compression and is trying to idle it right but keeps getting that piston with the low compression messing it up... also coudl be from the cams not being aligned right

[driftaholic]

here's how the physical timing is set up:







it looks right as far as i can tell.

i didn't have the block milled, but i gave the cylinders a light honing. i hope i didn't hone em too much.....i used brand new pistons and rings too, so that should rule out out-of-round pistons and rings.

so yeah... time for a new block already? sheesh.

[Thee 240sx Owner]

Your cam timing looks off to me... the lobes on cylinder one are suppose to point completely opposite from each other.. and ya if they are new pistons i would have had the block milled and used bigger piston rings.. that would have probably been alot better

[InsanityInc]

he's using two exhaust cams, that's why they don't point the same direction as stock ones. Also, if that were the problem, the compression would be bad on all cylinders.

[driftaholic]

also, in that pic, they had rotated a bit clockwise due to tightening em down. they actually are how they're suposed to be

[NateDogg]

Hmm...Did you hone the block and put in new rings like I suggested? All the cylinder pressures should be within 15psi of each other. You have 2 out of 4 with good compession seal.

You can't expect an engine to run well on 2.5 cylinders can you?

[Smurf6x6]

It's your cam combo. I also had the same idle problem when I swapped to 2 exhuast cams. No matter how much you play with the cams it just won't run right, unless you have them shimmed properly and is a wastes of time just for 2 ehxuast cams. Just swap back it should take you less than an hour and you will be happy that you can sit at a redlight with out the car dying on you.

[InsanityInc]

His compression is down on two cylinders, that has nothing to do with the cams.

[driftaholic]

okay so in the last week i discovered that both cams were off by a tooth. apparently the crank had moved and wasn't on tdc when i installed the cams. so i moved the cams.

the car is MUCH stronger now.

definately better than stock. i don't have a compression gauge or timing gun, so i have to wait til my buddy can bring that stuff over. there may be hope for me yet...

i adjusted the idle screw, and when it's warm it'd idle between 850 and 1000 for about 30 seconds. the idle is kinda bumpy (which i expect from the cam).

now, if i let it stall, i can't restart it, but if i turn it off with the key, it'll start right back up. what's up with that? is it flooding if i let it stall? i have to wait a few hours before it'll start again.

thanks everyone for the suggestions.

[driftaholic]

okay i found out something useful.hooked up an safc, and it reads 760 mm Hg, which coinidentally is atmospheric pressure.on the back of head is a gang of vacuum lines with 2 sensors connected to it, but i took that out. i guess i need to hook those sensors back up...

now, will they get the right pressure if i just hook em into the line that goes from the fpr to the intake mani? cuz that's the only vacuum line i have left.

[driftaholic]

nevermind, the safc is reading negative 760 mm not positive.and it does not ever change.

anyway, i hooked up those sensors. they turned out to be solenoids for scv and egr, which i'm not using anymore anway. the car would bog like mad and try to stall when i let off the clutch so i'm prolly just gonna unhook those again.

[w1ngzer0]

are you using 91 or 93 octane? Just curious

[98s14inaz]

"It's your cam combo. I also had the same idle problem when I swapped to 2 exhuast cams. No matter how much you play with the cams it just won't run right, unless you have them shimmed properly and is a wastes of time just for 2 ehxuast cams. Just swap back it should take you less than an hour and you will be happy that you can sit at a redlight with out the car dying on you."

What are you talking about? That has nothing to do with his ****ty compression. The two exhaust cam thing works with out reshimming.

[driftaholic]

i had almost a full tank of 87 when my motor blew, so i was running the new one on that (!!). then i added some toluene so i'm estimating around 98 octaneluckily the gas mileage was crap and i used half the tank in like 80 miles.

[250sx]

I dont think that any kind of toluene mixture can get you 98octane from 87, not even from 92. unless its a race fuel your tinting your fuel with. about cams, has anyone tried using a degree wheel when installing cams on these motors?

[250sx]

Ijust noticed that your compression is way off. not sure what it should be but it looks that you dont have good seal on 2 of em. maybe rings or valves? anyone know what the stock compression is?

[CChaney240]

stock compression is 179 with a minimum of 151 and a difference of 14 between the cylinders.

[driftaholic]

the toluene i got is 114 octane.

i got my motor to idle. hooray!

there's a thread in online mechanic about the latest round of problems, and their solutions.

since the last timei posted in this thread, i discovered my cams were both off by 2 teeth. i think the crank must have moved when i was putting everything together.

i also needed a new mafs. so i replaced that and now the car runs great. lots of power across the rpms. need to recheck timing and compression and see where i am there.

[mackdaddy240]

I did a HC ka24de swap in my 90 and it ran great much better then a 24e. I blew the headgasket and so I tore it appart..... again. and put a new gasket in. now it wont start it has spark and gas Im wondering if the crank chain somehow moved ? because the cam chain is in time..

[driftaholic]

well take off the valve cover and see where the cams end up when the crank is at tdc. i did that simple check and discovered that, although the cams were in time with each other, they were not in time with the crank.

[mackdaddy240]

Well I did do that a couple days ago and found that the crank was out of time, but it wasnt simpl! I had to take my radiator out so I could get the impact on the crank bolt and I had to drain my oil and drop the oil pan and then I had to take the motor mount bolts out and lift my engine a few inches so I could get the cover off because the oil pump pickup wouldnt let me simply pull the cover off. after all that I bought a new tensioner set both chains in time turned the crank 2 revolutions and SLIP my chain jumped 2 links so now I have to wait on new chains and sprockets. My cars been stressing me out way to much lately. I believe that is why my eyes been twitching for 2 damn weeks!

[silencer.1]

Have you retested compression since changing the timing cause cylinder 3 doesn't look healthy at all. If it came back into compression then I'd chalk it up to bad valve timing but if it's still way off you need to re-assess your rings. Also, did the ticking go away?