BHG 7m bottom end (pics-a-plenty)

[kemicalx]

Hey guys,

As some of you may know i've been slowly (as quickly as funds will allow) rebuilding the 7m out of my mz21, i've pretty much sorted out the head. But after opening up the bottom end i'm not sure how much work is required, as far as i can tell it doesn't look too bad.

Anyway they say pictures are worth a thousand words,











what do you guys think? i know the cylinders will need honing, the piston rings replacing, and it would be wise to do the bearings and rear main seal. But besides that what else do you think should get attention? Does anything serious look like it needs replacing?

Cheers everyone,
Ashlin.

[Cressida91GLX]

I will say go for low KM Japan imported engine. And do all this work on the new engine and put it back together. This engine seems to be farked up. And the best bet will be to go for 1jz route if you plan to keep the car to your self. If do not intend to keep the car for long than a decent head-gaskit and ARP bolts/studs will give you 2-to 30K Km on this engine.

Having said that I replaced two 7MGE engines on my cressida. and one of them was under warranty. The one now in my car is a low km jdm Engine and seems to work like a charm. I havn't even bothered to torque its head to screw it up.

[gianttomato]

See that scuffing there, that looks bad. Like forget about honing bad.....

[slide86]

yeah those scuff marks dont look to good. you MAY be able to eliminate some of the problems with a hone, but it would be prefferable to get it bored. then you are looking at new pistons as well.....

you might want to gte the bottom end cleaned as well, not sure from the photos. but is that some surface rust on the crank, you dont want any od that.

id definetly replace the rear main seal and put new bearings in it. might as well while its apart!

as cressida91glx says, it might be easier to get a change over motor or a 7mgte or something. the cash you would spend on this motor just to get it back to normal would be half what you could get a \turbo motor for......just an idea!

[Mr DOHC]

you'd need a bore/hone, deck, acid bath, nead bearings incl aux bearings, basically, a full rebuild

[Mr DOHC]

how much did the head cost

if u can get some cheap pistons, maybe u should learn to do a basic rebuild yourself

pretty basic engine

[kemicalx]

hey guys appreciate the comments, just for the record this is a 7mgte bottom end, besides the scuffing on the piston (i think that may be the photo making it look worse than it really is) What is it that makes this bottom end clearly screwed? I'm happy to pull everything apart and clean it all up, depending how much oversized pistons will cost i'm happy to get the cylinders bored too.

The head cost me $100 and about another $100 on top of that to get it resurfaced and the cams checked for straightness

[kemicalx]

I'll take some more picture when i get back from work, but it's only the very top of the scuffing near the rings where you can lightly feel scratchs by rubbing a finger nail across them.

[Mr DOHC]

well, the crank looks ok, spin it an dif u see and marks what so ever take a happy snap and post them.

[kemicalx]

mmm i really don't see anything wrong with the bottom end bar the light surface rust on the crank here and there and i'm pretty sure will buff off with polishing wool, i tried getting a better photo of the piston scoring but it's hard to get a decent focus on it. As i said it feels pretty smooth up untill a couple of millimeters before the rings where it is quite noticable if you scratch it. I'll take it into an engine reco place and see what they say but presuming it (and the cylinder walls) are cactus. How much will a set of oversized pistons and rings set me back?

[gianttomato]

You might find that a set of aftermarket forged pistons will be better value for money. They should be quite easy to get even thru people like Rocket Industries (who unfortunately are notoriously slow and American Iron oriented).
Here's a set of JE forgies on ebay...
http://cgi.ebay.com/ebaymotors/JE-PI...31606649QQrdZ1

When the block is rebored and then honed, beware that the block material is of an unusual composition. It requires a different honing pattern - do a search on here (old forums) or performance forums.

I would get the crank journals measured - if they are within spec and unscored, then get the journals linished before you put new bearings in it. Consider some decent rod bolts and some head studs - again ebay is your friend. Ebay would be a good place to score a gasket set too - bring a chair with you when you get the quote from Toyota for a genuine set.

I would absolutely deck the block - that way both mating surfaces are perfect.

[kemicalx]

would i be asking for trouble if i got some of these cheap cast pistons?

here
and here

If they would surfice, i could just have my block bored .40 thou, decked, and replace the bearings. and i could probally get out of this reasonably cheaply.

[gianttomato]

They'll be OK, but I would definitely get the pistons (and whole rotating assembly) balanced. Balancing Services Australia in Preston does this for about $150ish from memory. If you plan on running higher than standard boost, I'd consider getting the crowns coated.

[kemicalx]

how much would it cost to get the crowns coated?

[kemicalx]

I've taken the block into the guys who have taken care of machining on the head. The bottom end will require boring, total costs are as follows:

Bored/Honed - $160+GST
Decked - $60+GST
Main bearings - $80+GST
Rod bearings - $50+GST
Pistons - $228+GST
Rings - $103+GST

All reasonably priced imo. My only real concern are the pistons.. They are hypereutectic pistons (a brand called Hypatec) for those of you who don't know this means they are cast aluminium piston with an with additional silicon content. Because of the silicone they have a reduced thermal expansion rate and thus can be installed with tighter clearances and make a nice seal. I’ve also read are 30% stronger than standard items.. However, hypereutectic pistons being harder are also a lot more brittle and apparently pretty unforgiving with engine knocking.

Presuming they are 30% stronger than standard items I can't see why they shouldn't be perfectly fine for my goals. I do intend on running higher than stock boost. 10-12psi but it seems so long as I’m vigilant in ensuring my car won't lean out they should be fine, yer?. I’d love to b able to afford some nice forged pistons and have peace of mind but this is my first engine rebuild and a) I can’t really afford it and b) if I stuff something up and destroy this motor I’d rather destroy $250 pistons than $700 ones , there’s always time in the future for a proper engine rebuild anyway