valve issues/ head issues 1986 720 frankenstien engine.

[napsZ]

i have a 1986 nissan 720 i should warn it is not in any way stock.

engine is a hybryd build, z20 head, z24 block and crank and rods, ka24de pistons.
compression is good with a running compression test of 120 at 650 rpm

ratio is 11.1:1

z22 intake manifold

weber 32 36 dgev 88 and 155 jets

 

i started it up for the first time and it has a awful knock coming from the head. its not rods, the knock is half crank speed. the valve clearance is in spec, no the valves are not smacking the top of the piston,i have covered the basics and a few less conventional possible causes. i am fairly stumped on this one if you have had any problems like this or have an idea on what to do here i would appreciate your input :)

[datzenmike]

 

Welcome to Ratsun... you have arrived.

 

The Z20 head. Was it from the Mileage option 720? Or the A10 car? Both had very small combustion chambers of an estimated 45cc. The Z20E head from the 200sx was the same size as the Z24 at 57cc. Just curious which one you used.

 

I know the KA24E pistons have almost 3cc of dish but the KA24DE pistons must have a huge dish in them. Are you sure they are DE and not E pistons? Do you know the DE piston dish and pin height from center to top of piston? 

[napsZ]

millage option 720, wanted to stay carbed for this one build.

yes i am sure they are ka24de pistons unless the box was wrong and evergreen hasn't mislabeled anything in the past, not to say they couldn't, but to my knowledge they are ka24de pistons. i am not sure on the specs for the piston. i was under the assumption they where identical to stock z24 pistons.in terms how far they come up the bore they are identical. as for the dish being any larger, not to the naked eye.

[ggzilla]

That's the trouble with modified engines. Stock Datsun engines are super reliable.

 

Have you checked the piston-to-head clearance? Should be at least .0012 mm.

[napsZ]

i did. we have isolated the sound to cylinder number 1 now. could a flattened cam make a knocking sound? it sounds very much like valv lash. piston rattle perhaps? a wrist pin that is not dead center maybe?

i have gone through and test all these things but i am considering going back and doing a re check again just for the hell of it :P

[napsZ]

i should point out that it sounds like valve gap but it isnt. but the sound being made sounds very much like valve taping.

[ggzilla]

So not a knock, but a tapping/clicking sound? Do you hear it at idle, or only when revving it?

[napsZ]

all rpms

[datsunaholic]

 

The Z20 head. Was it from the Mileage option 720? Or the A10 car? Both had very small combustion chambers of an estimated 45cc. The Z20E head from the 200sx was the same size as the Z24 at 57cc. Just curious which one you used.

 

 

Really?  Because when I replaced the banana head on my '81 510 with a '81 200SX head, they were identical in every way, except the 200SX had a block off plate where the fuel pump went.  Of course, the 510 engine had flattop pistons (with valve reliefs) in it was well.

[napsZ]

well i closed the door and the window shattered. i'm putting this on my back burner and i'm afraid i'm working on my 2 crxs and gonna drive this engine until it bursts its little walls and dies than i'll rip it apart and tell you all what i did wrong and why not to do this type of Frankenstein build. apart from all the reasons that good sense has already dictated. if it lasts 20k i will and its sounds like a tick but a fairly loud tick.

[napsZ]

i think in short i built a far too complicated datsun and found out why no one builds high compression wacky naps z engines. even after all this work its only about as fast as my 2007 tacoma 4 cylinder

[ggzilla]

Good point. The Tacoma has a bigger engine (2.7 litre), more valves (16 compared to 8), and variable valve timing. No way compression is going to bear that. Even using a stock Nissan KA24 is now more popular than a hybrid Z motor.

[napsZ]

yah it was a good engine stock and did what it was supposed to do well. but the l series and k series have alot more tuning potential. will a ka24de bolt up to my 5 speed?

[ggzilla]

L-series will only make about 150 hp heavily modded for street

 

The 16-valve engines make over 150hp stock, both the Nissan pickup KA24DE and the Tacoma 2.7. Stock reliability too.

[napsZ]

these numbers sound so happy right now. but i am so disappointed right now i'm fuming. 6 months of running to and from helena to belgrade. only about 600$ in the build though. all for a rattling pile of trash. oh well win some loose some i'm gunna go find a cheep hooker to express myself in a meaningful and contemplative way. and have the phrase "your life is like that awkward hard on you get when you watch deliverance" bounce around my head for a few minutes.

[ggzilla]

Just fix the Z24. Probably a bad rocker.

[napsZ]

we checked that out, nothing was out of round no gashes or even bearing blemashes. the springs where in spec and so are the tap-its the cam is smooth and not flattened and there is no play in the cam bearings/ bushings.

i'm a qualified tech like ASE and everything! and even college for automotive tech. my profs told me there would be engines like this where nothing makes any sense until you have a catastrophic failure. i'll wait for a failure than rebuild my old z24 head and just have a normal pickup truck.

[datzenmike]

What rods did you use? the KA-E rods and the Z24 are interchangeable. Pretty sure the KA-DE pistons are different so only DE rods would work.

 

KA24E pistons on a Z24 engine with a Z20 head makes 11.76 compression.

 

 

This is an E piston.... look like the ones you used?

[napsZ]

stock z24 rods

nope the one i used and the stock piston had deeper dish and very slight valve reliefs

[napsZ]

the piston on the left

[datzenmike]

That's my Z24 and KA24E pistons.

[napsZ]

ok. the piston on the left was labelled and sold to me as a ka24de piston. it may very well have been a z24 piston i took out of my engine and a mislabeled z24 that i put back in. i build primarily hondas and i haven't gone in depth into nissan and datsun i figured what i got was what i ordered. regardless, it is not likly to be the source of the sound. because i replaced all the pistons and if it was an issue it would very likely manifest itself in every cylinder.

[datzenmike]

KA24DE pistons are not used in L/Z hybrid builds. There are some differences that make them unsuitable. I haven't seen one but likely the pin and the rod small ends are the problem. I don't think the DE piston will fit a Z 24 or an E rod. Could be wrong but... 

 

 

Were the pins pressed in or were they held in with C clips?

 

I guess pull the head off and see if a piston is hitting the head.

[napsZ]

the pistons where identical to the ones i removed from the engine. the wrist pins where pressed in. i gotta wait for more money in a bit here but when i get my next paycheck i'll buy a new head gasket and check. how ever i say again, i changed all of the pistons. if it hits on cylinder 1 it would hit in all cylinders.

[napsZ]

i just got my new shop press so i can do all the work in house now and i have a new alternator on the way cause the old one died on my test drive, and new glass and head gasket. so i will be getting back to this project in the next few weeks. i have a crx that needs new suspension bushings more than i need a truck. and i have a motorcycle that might be getting nitrous so i have some more interesting projects that are ready to happen lined up for a little while here.