4AGZE Gurus Pls Help : Engine developed knocking sound

[Ghetto-Spec .:bayka:.]

Hi PPL, havn't used this new site since the end of the good old days of toymods.org but I really need some help!

-- the car --
AE93 with AE101 4AGZE engine conversion. Standard internals, std boost, ultimate 98 fuel only, vl turbo fuel pump and surge tank.

-- the problem --
Engine has developed a knocking / clacking sound that appears to come from the head. It initially started out at about 3500 rpm, and only under load, but has since spread over the entire rev range and car has been taken off the road. The car is not blowing any smoke but has lost noticable power, it idles fine but as soon as it is revved above 1500rpm an oscillating metallic clacking sound occurs at quite a high frequency. It sounds like a broken valve or valve seat or something. The RAC dude used his stethoscope to try and pinpoint the noise origin to no avail, however was able to prove it is not bottom end. (ie not gudgeon pin)
Pulled off rocker cover and bucket/shims are all visually OK. Compression test came up OK, spark plugs are all OK, and we have pulled cam gear cover off and the timing looks OK.

Any suggestions, similar encounters before?!

We suspect it may be a damaged valve that still works at idle (seals) but fails and makes a lot of noise when reved above idle. We just want to do as much as possible before resorting to 'pull off the head'.

I just spent $2500 on new drive shafts, oil, gearbox seals, 5 puck ceramic plate clutch centre, trd pressure plate and VOLK TE37 immitation rimz along with putting in countless hours of manual labour at night after working full time, to drive the car for 2 weeks ONLY before this problem. I really need help on this guys, im not a good person anymore with my car like this, im a bitter, cynical bastard

[slide86]

you may have a damaged valve, or broken spring....

the buckets may look ok visually, but there may still be a damaged lifter there. lifters often make a clacking type noise when they are no good. try pulling them out one by one and try to compress them, if there is one that you can squeze with your fingers then that one is no good. you shouldnt be able to compress them with your hands.

thats what i would be checking out, the comp test came up ok which is a good thing for you. probably not a damaged ring then.

[EVOSTi]

im guessing big end bearing.

[wiso]

this may sound really dumb what i am about to say, but hey who knows.

i did my timing belt a while back and after getting it back together it had a horrible rattling/ knocking sound, i had a few guys look at it they kept saying lifters, lifters, but i hadn't touched the cams, quick drive around the block it was slow, the sc was coming on, but not producing much boost.

anyway after starting to pull it apart again i found the water pump pulley bolts were loose so the pulley was knocking around, must have been effecting the belt wrap on the sc causing it not grip well and to boost fully.

i know, i said it sounded stupid, but hey, it happened to me

[kingmick]

im guessing big end bearing.

that is more than likely it! unlikely to snap a spring, and you would notice it in the exhaust note if you did.

[willwal98]

i'm no 4agze guru but i'd be checking clearances around those buckets. Even a slightly larger clearance will make a noise. I don't know alot about the 4agze actually but i'd also agree with slide about the possability of spring problems.

[EVOSTi]

well being a boosted motor, big ends are the first place id check. and being FWD, its not that hard to rip the sump of and have a look.

[wiso]

easyiest way to tell if its a big end would be to drain your oil, if there is metal shavings through it, it means one of your bearings has let go

[kingmick]

well being a boosted motor, big ends are the first place id check. and being FWD, its not that hard to rip the sump of and have a look.

lol fwd makes them a pain in the bum to drop the sump off! lol

[kingmick]

easyiest way to tell if its a big end would be to drain your oil, if there is metal shavings through it, it means one of your bearings has let go

you mean can open your filter!

[wiso]

well pehaps, i guess if he has been driving it for a while yeah he may hat to cause it may all be through the filter now, but i remember when i did my big end i drained my oil and had metal shavings all through it, so did my mates and when we took the sump off there were shavings all int he bottom of the sump

when a big end goes it all the shavings will eventually go out the sides, and will drop into the sump, from there it won't get picked up again because of the filter on the oil pickup to the pump

[EVOSTi]

i wouldnt go just by the oil, definately take the sump off.

and yeah on AE92's its not that bad, just take the front part of the exhaust off. a little easier than on the AE86 as the crossmember is in the way.

[slide86]

this goes against my last post, but i didnt want to condem the engine straight off. but everyone else has so......my GZE spun two main bearings and made a knocking/rattle noise all the way through the rev range. i had to get the whole engine machined up to get it fixed.

i didnt want to say before cause i didnt want to shatter your dreams....the others did it for me!

[EVOSTi]

well better to hear the worst case scenario straight up. and yeah i recently rebuilt a gze running a turbo, had similar symptoms, 2 big ends shot, send the crank away to be checked and it was cracked.

[tooch]

You could try a leakdown test to see if its a valve issue, then you can listen to where the air (if any) is leaking from, to ascertain if its an intake or exhaust valve.

Although seeing as your comp test came back ok, it probably wouldnt help.