Understanding Complexities of a 4age 16v Smallport rebuild

[trd_st184]

Hey all,
Part of my new project/daily will include rebuilding a 4age 16v 100kw motor out of a Corolla SX.

I ended up sourcing a Seca SX model, and the motor was described as having the "valves leaking" which I presumed might have been valve stem seals, or compression loss.

Its my one big opportunity to build up this 4age just the way I want

I've done head gaskets, engine conversions, suspension work, auto to manual conversions and most types of of engine repair at least 3-4 times (thermostat, timing belt changes, rear main, front main, radiator swap, cam removal and installation).

Now there is no doubt quite a jump to actually rebuilding an engine, but the only area i've never touched is the big end side of things. I have a lot of patience and an attention to detail so i'm sure I will have no problems doing all this myself.

Can I ask what sort of costs could be related into machining for having to put oversized bearings in (if the surface needed machining)?

The bearings seem to still be in good nick on the car (hasn't spun a bearing) so hopefully the crankshaft journals will still be in good nick.

I would need to get the valves relapped, head machined flat and if need be the valve seats may need attention.

My extent of the build is not confirmed yet. But i'd love to chuck in a new set of pistons, titanium valve spring retainers, a better set of Valve Springs and a set of 256-264 degree cams to boot.

The block would need to be honed if the bore is still in good nick, but its good to know what the costs of reboring would be if I needed oversized pistons 10 thou usually?

I've got a torque wrench, so following the workshop manuals and a bit of intuition i'm sure its acheivable. Its the one thing i've always wanted to do.

At the moment i'd likely just be using the stock ecu for convenience. Aftermarket may come into it at a later stage. The stock ecu will run the 256 cams reasonably well from what i've read
Any advice would be tops thanks

[maj]

I've been quoted around the $1100-1200 mark for a machine shop to do the following. My aim is an OEM quality rebuild. Price will vary so take it as a ballpark only.

block acid tub and crack test (around $200 or so and then have the option not to go any further if things don't look right)
decking the block and rehone cylinder chambers
supply new piston rings to suit rehone specifications (this is if I can still use my stock pistons, otherwise supply 0.5mm oversize)
check crank straightness and linish
supply new mains and rod bearings to suit
remove valve spring retainers, valves and springs, check everything
head acid tub and crack/warp test (again similar to above, can decide to stop here if need be)
head skim and install stem seals to be supplied by me (OEM toyota)

All disassembly/reassembly to me done myself, which I'll be having someone with engine reassembly lend a hand to ensure everything looks fine.
I am also going to opt for a rotating mass balance which adds another $200 on top.
You have more experience than me; prior I have done exhaust swaps, intake removal/vacuum hose diagnosing, replacing CV boots, cooling system parts replacement etc. And thus far I've performed an engine teardown without too much difficulty, so as long as you are patient and have an eye for detail, you shouldn't find a 4AG rebuild too hard.

<this is the part that is up for discussion, please do not take my word as gospel as mentioned I've never rebuilt an engine myself>

I've found the following are a good starting guide for consideration:
- You are looking at increasing HP but running stock engine management, so any major changes are not going to reflect well. I'd try to keep CR close to factory, maybe no more than 0.3 increase? Someone can add a little more here. On my GZE I wouldn't go more than 8.5 on a stock 8.0 CR. Easiest way around this is just to run an engine and ECU with better CR, eg. a 8.9 CR AE101 GZE engine and ECU.
- Any changes that will affect AFR will not go down very well on stock engine management. You'll find yourself running lean very quickly and an engine that might not last more than 10-20,000kms due to detonation.
- Increasing bore unnecesarily will shorten your blocks lifetime. If you blow rings again and need another rehone you'll be a lot closer to the limit of what the block can reliably take. If you have a 3-rib 4AG then this might be even less due to less block reinforcement.
- Running up to 256 cams sounds fine for stock management, but just remember the above advice. It's not a hard and fast rule that those cams will work despite other modifications also done to the engine.


If you pull off the head and find your bores look fine, is there much reason to touch the short block straight away? I would rather look into getting the head port matched and possibly 5 angle valve job. Get the head breathing better and you'll find a nice increase in power over factory, which would be even more beneficial for a cam upgrade. You can then go even further with more aggressive cams and aftermarket ECU, and just keep driving it until you finally do need a bottom end refresh.

If you have to get the bottom end done, definitely get it all balanced, but then it's up to you how far you want to take it, budget increases quickly when you start thinking about replacement pistons and rods etc.

[trd_st184]

You always reply to my threads, I really appreciate the time you took to write all of that for me.

I must admit I would be quite content with the stock 100kw motor, but my main limitations is tuning. I think even with stock replacement internals I would be quite happy, the one thing i've always wanted was a streetable cam in a 4age. Still working within the legalities some improvement in overall feel and idle (a bit more lumpy hehe) would add to the whole feel of the car quite considerably.

Would there be any concerns salvaging my old pistons if required? I think long term bolt ons will be the preferred choice of upgrades, still while trying to fall as closely as possible within factory ECU spec (which is quite limited i'm sure).

As an option i'd still just like to upgrade certain components to fall well into making reliable power (maybe 155-160hp at the fly as per Billzillas guide)

[maj]

If your block needs a rehone, shouldn't be any issue reusing pistons, just get them checked while they are out to ensure they're still in spec and have no damage around the ringlands etc.

I don't want to put anyone offside on this thread, but your initial intentions are very similar to mine when it comes to streetability and need to refresh at least some of the engine. In my case I want to keep stock engine management in order to qualify for historic rego, so any mods for me will always be mild.

I say as long as your bottom end is fine, slap on a TRD headgasket for a tiny CR increase, get your head flowing well, run it in and see how it performs, try to get some AFR reading gear if possible so you at least have an idea how the engine is running. Once everything is shipshape, chuck some bigger cams in and check everything again to see if it's still happy.

If your bottom end does need redoing, maybe try to keep it within factory tolerances (keeping stock pistons if feasible, engine bearings are nice and tight), balance your bottom end then use ARP studs etc. instead of Toyota ones as they can put up with a lot more stress, then just follow the same recipe as above when it comes to the head.

At that point it can be completely up to you if you'd like to take the build further. You can then go aftermarket management and increase fueling and spark efficiency as well as the whole ITB stuff etc. to wring as much HP as you can out of it.

[dnegative]

Building good OEM spec engines is not hard, you just need to be meticulous and know what your doing.
If you can follow a service manual and understand why your doing the things it asks you should be alright likewise when your off getting machine work done as you always check their work.

[rick q]

One thing I've found useful is to have a shoe box and a stack of zip-lock bags. As you pull the engine down, everything associated with the part you take off goes into the bag and gets labelled. The bag then goes in the far end of the shoe box. Keep doing this [dismantle - bag - label - into the box] until you're done. Photograph everything as you go.

When it's time to put it back together, start at the last bag you put in, and work your way back to the first bag. Keeps everything together and gives you a clue to putting it back together again.