GameboyRMH MegaDork
Jan. 11, 2017 9:48 a.m.

Looking for options for fixing the greatest automotive disaster (and most expensive repair job) of my life, a burnt piston and scored cylinder. A potential project-killer and hobby-ender for sure. Options I've had to rule out due to cost include new overbore performance pistons, importing a block, and a full set of sleeves.

A set of used stock pistons (redtop or silvertop) and sleeving on the damaged cylinder only could be an affordable solution, but does anyone know if the 4AGE block is structurally up to taking a single sleeve vs. a full set? A full set is definitely not affordable, like I said.

Another affordable option could be overboring to a yawning 83mm and using Mazda BP pistons. Decent idea or or asking for trouble?

Of course a used block and pistons are theoretically easy and could be affordable too, but then there are the unknowns of actually finding a good block, or even any block locally. I'd say the hassle of registering a new engine number with the DMV-equivalent here is worth at least $100, so I'm not too enthusiastic about this solution.

Dr. Hess MegaDork
Jan. 11, 2017 10:05 a.m.

Why did the piston burn? Intake leak there? Bad injector?

Really, GB, get a new used motor. Tough about your import regs and all, but try to figure a way around/through that. If you can save up the money and buy a silvertop, re-do the code on your megasquirt and you would be ready to go. At this point, I think you are throwing good money after bad by sticking with that current motor. Aggie-rigging something like you describe is not going to get you where you want to go. Probably literally.

GameboyRMH MegaDork
Jan. 11, 2017 10:32 a.m.

I don't know what caused the problem, could be a too much advance in one area of the spark table as seen in the build thread, could be a failing injector. Never heard any pinging from the engine though. I've got a new safer spark table ready to go and I'm going to have at least the injector on the damaged cylinder inspected.

I'd be throwing a lot of money away if I go with a completely different engine, on top of the purchase price. Any reason to go with a whole different engine vs. a used block and piston set?

Dr. Hess MegaDork
Jan. 11, 2017 10:44 a.m.

It's probably cheaper to get a whole new engine than mess with what you have. You could sell off some of the custom stuff on there to partially fund it. And you would have a good, complete motor.

When I melted a piston in a Europa, I never heard any pinging. I did find one intake manifold O ring hanging loose. That was my lesson in letting other people build my engines.

Anyway, I don't think that just too much advance would necessarily do that. The 4AG is a pretty tough motor. I ran my 20v in the Rolla pretty darn lean with plenty of advance and never had a problem.

GameboyRMH MegaDork
Jan. 11, 2017 10:58 a.m.

Huh the intake leak is an interesting possibility. My engine was running a rather rich tune for safety.

Edit: Should also add that's it's not any easier to sell 4AGE 16v parts locally than it is to buy them.

I'm having the mechanic check the exact depth of the damage right now because I found some 0.030" overbore pistons that could work. Would be great if they can, but I should know by now not to get my hopes up.

NickD SuperDork
Jan. 11, 2017 11:07 a.m.

Are the valve reliefs in the right size and location on a BP piston for a 4AGE head? I highly doubt it. So, then you have to get into flycutting valve reliefs, which is a pain, and is reliant on the pistons having enough meat in them to get a big enough relief. And then you'd have a bunch of valve reliefs that would kill compression, screw up your flame front and accumulate carbon (causing hot spots that cause detonation and pinging)

edizzle89 Dork
Jan. 11, 2017 11:32 a.m.

another thing to look at along with the the leaking intake manifold is maybe the injector for that cylinder is half clogged up or something not letting it get full fuel

GameboyRMH MegaDork
Jan. 11, 2017 11:34 a.m.

I know Keiichi Tsuchiya himself once built a 20v "7AGE" with BP pistons, but after researching where that went, it turns out it later blew up while filming one of those touge I think I can cross that idea off the list!

GameboyRMH MegaDork
Jan. 11, 2017 1:04 p.m.

I'm trying to find out now if the ITM RY6446-030 piston has the right wrist pin diameter for my rods (20mm). If so, it can turn this clusterberkeley into a routine overbore.

oldeskewltoy UltraDork
Jan. 11, 2017 3:17 p.m.

I have a few used high comp pistons(not O/S).... they'd fit in a USPS box.....

are you sure it needs a full 1mm overbore? You might find a set of these.... TC2989 .020 they are the aftermarket equivalent to the 10.3:1 slugs, and they are .020"(.5mm) over

GameboyRMH MegaDork
Jan. 11, 2017 3:56 p.m.

Had the mechanic measure the damage today, he says I need at least 0.5mm overbore so 0.020" can work. Found a site that has a set of those TC2989s for under $70 so I'm going for those now!

ae86andkp61 HalfDork
Jan. 11, 2017 4:08 p.m.

If I were in your shoes, I'd shy away from an 83mm bore. IMO, an 83mm bore to reduce the cost of pistons falls under false economy. I'm not sure the reliability is there for anything built on a budget and/or used as a street car as well as a race car, especially when 81.5mm and 82mm pistons exist, if not readily available on your island.

Maybe you've already looked into this option, but how is local availability of "lesser" A-series blocks? Sure, if shopping for a complete engine you'd want a 4A-GE, but for just a block, can you find a 4A-C or 4A-F locally? A 7A-F block could also work in theory, but requires more work and wouldn't be as cost-effective.

GameboyRMH MegaDork
Jan. 11, 2017 4:35 p.m.

Yeah I ruled out the 83mm Miata pistons after I found out what happened to the only known swap of such pistons. I've just ordered +0.020" (just over 81.5mm) TC2989s.

oldeskewltoy UltraDork
Jan. 11, 2017 5:56 p.m.

ae86andkp61 does have a point! You might keep your eyes peeled for a mid 90s 4AFE... block is 7 rib and should work well....

As to running the 7A block, that might be fun too.....

GameboyRMH MegaDork
Jan. 11, 2017 7:32 p.m.

I have an early 90s oil squirters though.

oldeskewltoy UltraDork
Jan. 12, 2017 4:22 p.m.
GameboyRMH wrote: I have an early 90s oil squirters though.

oil squirters were never on the earlier engines... besides the squirters didn't seem to help you... (not trying to be a wise a$$)

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