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1988 Corolla SR-5
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Discussion Starter · #1 · (Edited)
I have installed the pistons from my "broken crankshaft" 4A-GE into a 7A-FE that I am reconditioning. The intent of this mod was to increase the compression, to see if this might be an easy way to increase the power output of the 7A-FE.

The result is an inteference engine.

The 4A-GE pistons and pins fit quite nicely on the 7A-FE rods.
With the timing belt installed (and timed) everything clears. I did not have putty to measure how close the pistons and valves come to each other, but with the timing belt off, there is contact.

Both piston crowns come up to about the same level in the cylinder. The 7A piston has a recess in the top, whereas the 4A-GE piston has a slight dome with valve reliefs cut in it.

The difference in the angle at which the valves are set in the heads means that the narrower included angle of the 7A valves cause them to contact a part of the 4A-GE piston dome where there is no relief cut into it.

This installation was with the 7A head gasket. Maybe with the 4A head gasket it might clear, since that is a thicker gasket.
Unfortunately, that will bring the compression back down a bit, making this a questionable exercise, since I have no idea how much the increase might be to begin with.
 

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I was going to say that it will work, you will have high CR, but it will be an interference motor... the cutouts for the valves are at the wrong angle
 

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Discussion Starter · #3 ·
A 4A-FE head gasket did the trick, my 7A-FE with 4A-GE pistons is no longer an interference motor.
The 7A-FE gasket is 0.7mm thick, and the 4A-FE head gasket is 1.4mm thick. That extra 0.7mm was enough to get clearance.

The engine is now almost completely built up. The crank, pistons, head, oil pump, oil pan and water pump are installed.
I think I will need to get a SR-5 radiator as the water hoses are run differently between the 4A-GE and the 7A-FE. I had bought a Civic aluminum radiator for that reason, but I now think it is too tall for the coupe body.

Tomorrow I hope to be able to install the light weight flywheel and clutch, and maybe even attach the gearbox.

The 4A engine and gearbox are still in the car, and I haven't done the wire harness swap yet, so I will probably be very busy this week.

Oh! for those of you who don't already know, the original plan was to swap the 7A-FE into my 1989 GT-S temporarily, while I try to find a 4A-GE smll port cylinder head and pistons, to make a 7A-GE.
If the compression increase I am trying to achieve yields reasonable performance, I might just keep the
hi-compression 7A-FE and not bother with the 7A-GE.
 

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Why bother with all the work to get the 7afe running in your gts just to redo it all anyways? just slap your head on it and be done no need to mess with the wiring.
 

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Discussion Starter · #5 ·
Why bother with all the work to get the 7afe running in your gts just to redo it all anyways? just slap your head on it and be done no need to mess with the wiring.
Well, (1) my GE head got screwed. When the crank broke, metal shards got up into the cam journals and chewed up the head and the cams. If it was good, I'd put it on and be done with it.

(2) Many people decry the 7A-FE as a piece of crap, although for stock Corollas the 7A-FE powered DX, posted one of the quickest 0-60 mph times, I think beat only by the FX16 GT-S (a lighter car). That doesn't take into account the models after the AE101, I haven't seen figures for those.
If this engine performs satisfactorily, I might just keep it the way it is.


Modification: When you change something to what you think it should have been from the begining ;)
 

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I missed the part about your head being toast, I have a small port head with no cams but complete otherwise, I also have two bigport heads, I just don't know how bad shipping is going to be for ya crossing the boarder.
 

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Discussion Starter · #7 ·
4doorGTS, you got PM.

Also, If I go to a small port head later on, I can run it with the 7A ECU and wiring. Won't need to use the AFM, no TVIS.
 

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Discussion Starter · #8 ·
The 7A engine and gearbox are now installed.

I also put on an OBX 4-2-1 header. It almost fit perfectly in my GTS, but it comes up about 2" short of the catalatic converter. I'll have to have the muffler shop strech it a bit.
I also had a fitment problem at the head, where the alternator mount bracket and the header needed to occupy the same space. I had to do some grinding on both of ftem to make it fit. I have installed OBX headers twice before, and they fit perfectly. This one surprised me.

My '95 Corolla wiring manual just arrived, so I am starting the wiring process. As mooreofit said in another thread (7A-FE engine for AE92 sedan), it is not a job for the faint hearted. You definately need to be able to read a wiring schematic, and have a lot of patience.
 

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4doorGTS, you got PM.

Also, If I go to a small port head later on, I can run it with the 7A ECU and wiring. Won't need to use the AFM, no TVIS.
you can, but then you need to find a very difficult to find distributor.
 

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The Return of the Red Coupe
2010 RAV4 V6
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I missed the part about your head being toast, I have a small port head with no cams but complete otherwise, I also have two bigport heads, I just don't know how bad shipping is going to be for ya crossing the boarder.
Too bad it's not a complete smallport... otherwise I'd be interested. :(
 

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I almost feel bad having as much stuff as I do here...... nah.

7afe vs 4age smallport piston (both on a 7a rod);
 

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AE92DX 4AFTE
ae92
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so were you just lucky that the wrist pin diameter was the same??? so smallports and 7afe's are the same but 4age is fully floating?

i am starting to piece my large-port 7ag together and i don't want the wrong pistons...
 

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so were you just lucky that the wrist pin diameter was the same??? so smallports and 7afe's are the same but 4age is fully floating?

i am starting to piece my large-port 7ag together and i don't want the wrong pistons...
not lucky.....

early 4age's have 18mm full floating wrist pins
later 4age's, smallports, ST 20V's, and 4agze's all use a 20mm full floating wrist pin

7afe uses a pressed 20mm wrist pin
 

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AE92DX 4AFTE
ae92
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what about 1st and 2nd gen 4afe? the reason i ask is that i have a 7-rib 4af short-block and if i can just buy a gze crank, rod, and pistons and be done!!!

since i'm still using the 4afe head which isn't good for high-rev, would forged rods be a giant waste of money???
the reason i ask s because i always think of rods for high revs and pistons for taking boost/compression so i should only need the crank, oem rods and forged pistons right??? (staying under 18psi with MS)
 

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AE92DX 4AFTE
ae92
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OH and i Dyno'ed again yesterday i will scan the updates and post today
 

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you can stick with a 4age crank... all cranks should be the same....

the advantage to finding a latemodel 4age block would be at least the taps for piston oil squirters.... a good idea for you to have.

Unsure if the later 4afe blocks have those.... the main bearings between a 4a and 7a are the same... you can use any 4a crank in any block.... the 7a wont' fit due to counterweights being too large....

if you can find stock smallport 4age or first gen 4agze rods you should be ok on boost... but if you want the satisfaction go for aftermarket....


bigport 4age, late smallport 4agze, smallport 4age
 

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Discussion Starter · #17 · (Edited)
Ok. The engine is in.
The wire harness is in, temporarily. All the wraping has been removed from the sections going to the relay box and into the cabin, until I get everything routed correctly and working, then I will take it back out and re-wrap it all.

I got it started, but it won't keep running. It will fire for about two seconds and then die.
If it had a MAF sensor, that would be my first suspect, but this engine doesn't use MAF, it uses MAP.
I checked that and it is good.

Tomorrow I will start troubleshooting to see what I have wrong in the wiring. ............. Any suggestions?

This system uses two O2 sensors, but I only have the main one in.
The second one is supposed to be for monitoring the condition of the catalatic converter, and not affaec the ECU opperetion, so I doubt that is the problem.

Somebody suggested the Idle Air Control valve, but that only works with the throttle closed.
I opened the throttle, and it still dies.


One other thing. With the GE pistons, the compression reads 205psi. I am not sure what that equates to in C/R, but I think that is good.
 

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AE92DX 4AFTE
ae92
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i'm sure i'ts well over 10 but i hope not much higher or you will have to retard your timing as though you were boosting... not worth the trouble IMHO
 

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I would suspect the fuel pump..... old maf wiring had it wired directly into the afm then through the csi, whereas map systems have the ecu turn it on then via the csi.....

on initial fire the fuel pump will kick on.... this sounds like the very common ae86 problem of start and no run (which is ALWAYS the fuel pump)
 

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AE92DX 4AFTE
ae92
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ahhh yea i forgot to pull my efi relay once and my stock 4afte which is about 9.5:1 was 205 exactly normally it's around 186ish (new is 190)
 
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