Pro ViZIon

Ok so I'm trying to get my twin cam swap started up (I have to reset the timing) and when I'm trying to crank it over by hand it stops at some point and gets extremely hard.

Does anyone know why this would occur?

Also when I crank it with the starter I hear a knocking kind of sound. I would like to know what that could be as well.

Anyway thanks in advance.

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1990 Nissan 240SX w/KA24DE - New project
1984 Mazda RX-7 GSL-SE 13B

hessianben

um, you most likely are hitting valves with the pistons.

enjoy the rebuild.

when you say (i have to reset the timing) do you mean the cam timing? as in, you are off a tooth on the chain?
if so, then you have definitely bent valves and possibly damaged pistons.
the reason for turning the engine by hand first, is to find if anything is hitting, and if so, to fix that before allowing the much stronger starter to spin it and cause damage.

if this is the case, you're going to have to pull the head and start over with valve work.

roboticnissan

Sounds like hitting valves to.me too.

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Pro ViZIon

OMG NO. I hope that's not the case.

Oh and by timing I was refering to the ignition timing.

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1990 Nissan 240SX w/KA24DE - New project
1984 Mazda RX-7 GSL-SE 13B

Schassis707

if it isnt the valves it sounds like bearings to me

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angels12

bad timming, valves hitting the pistons

jacobs13

Definately pistons hitting valves. How off is your timing and how many times did you crank it and hear this knock? If it was only a few cranks you may be ok but removing the head alone is an exspensive task having to buy new head bolts and gaskets. Do a leak down and compression test to find out if you did any real damage. Also why did you mess with the timing in the first place?

Pro ViZIon

Again this is all ignition timing I was trying to reset.
I had just got the motor and the distributor wasn't secured in the motor.

Would it be a lot to just swap a new head over?

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1990 Nissan 240SX w/KA24DE - New project
1984 Mazda RX-7 GSL-SE 13B

hotlavaflow

Do you know if the engine was running before you got?

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Pro ViZIon

That's what he was telling me. Its got 93,000 miles on it.

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1990 Nissan 240SX w/KA24DE - New project
1984 Mazda RX-7 GSL-SE 13B

S14Driftn4life

sounds like you got a bad motor no doubt in my mind that you were hitting the valves. pull the timing cover off and the valve cover and redo the whole timing before its too late. stop cranking it now!! or your going to be rebuilding the head

Pro ViZIon

Ok well i got the cams timed now and the motor turns over smoothly with no problems.

I tried starting her up to no avail. I guess i need to check whether there is any spark and other things. How would i check if the ecu is getting any power?

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1990 Nissan 240SX w/KA24DE - New project
1984 Mazda RX-7 GSL-SE 13B

hessianben

sorry to say, but if you spun the mis-timed motor with the starter, those valves are bent.
do a compression test or a leakdown test just to make sure- maybe you got lucky and nothing broke.

to leakdown test each cyl:

- move each cylinder to Top Dead Center- you can visually check this by inserting a clean rod into the spark plug hole and rotate crank by hand until the piston is at the top of it's stroke. remove rod and connect your leakdown guage. pressurize and see how fast it loses pressure.

to compression check:

if you are SURE that it is now cam timed and there is no mechanical interference.

connect comp tester to spark plug hole and spin motor with starter for a few revolutions (with all plugs disconnected from wires)

they should all be within 10-15psi of one another (usually around 170psi)

if your compression is low or your leakdown is high, you probably bent valves.
disassemble and start over with new stuffs.

Pro ViZIon

Can I swap a 95 head over to my 93 motor. I haven't checked the compression yet but I may be able to buy one.

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1990 Nissan 240SX w/KA24DE - New project
1984 Mazda RX-7 GSL-SE 13B

Pro ViZIon

ok i did a compression test and the results cam back pretty bad.

Cyl. 1- 115psi
Cyl. 2- 50psi
Cyl. 3- 90psi
Cyl. 4- 105psi

I even put oil into cylinders 2 & 3 just to see if maybe the piston rings were bad too but no change in pressure so thats good i guess.

So it looks like my valves are totally bent up.

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1990 Nissan 240SX w/KA24DE - New project
1984 Mazda RX-7 GSL-SE 13B

240sxrb25

thats not so bad. its just your valves saying goodbye to you.

roboticnissan

Head rebuild time. If you decide to swap to that 95 head you may need to use that same year intake and exhaust manifold. If you do then you will also need that years wiring harness.

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hessianben

might as well get down to it!

since you've got things apart, you may as well check everything else for damage- pistons ect...


and a Cometic head gasket wouldn't be a bad idea... especially if you feel like going ka-t later on!

Pro ViZIon

Ok I took off the head today and the valves look fine to me. What is the problem.

Is my motor just screwed?

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1990 Nissan 240SX w/KA24DE - New project
1984 Mazda RX-7 GSL-SE 13B

hessianben

Can you see tiny crescent shaped marks on the pistons?

Pro ViZIon

Yeah I inspected them and didn't see any of that.

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1990 Nissan 240SX w/KA24DE - New project
1984 Mazda RX-7 GSL-SE 13B

hotlavaflow

Don't bother with a Cometic headgasket just use a Felpro you don't need the headache unless your built for high boost. I run up to 15lbs on my Felpro no problem. I have a Cometic but I won't install it till I'm ready for 15+. Your block and head have to be machined to ensure a proper seal with the Cometic.

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Pro ViZIon

I'm just rebuilding the motor. Sorta.
I did get a cometic headgasket, arp head studs. New piston rings and connecting rod bearings.

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1990 Nissan 240SX w/KA24DE - New project
1984 Mazda RX-7 GSL-SE 13B