bobchiba

Hey Folks, tempted to use the lockdown situation to actually finally man up and have a go at getting my hands dirty for once and take a crack at replacing the rods on a 1.8vvt. I already have a Turbo'd mk2.5 at 240bhp and was debating using my usual tuners to simply replace the rods to allow a re-tune to maybe 280-290, as they've done several similar builds. They said they'd charge no extra to fit a 6spd box too If I sourced one so looking at about £2k. Whilst this is very reasonable for a trusted UK tuner I feel like even if i f*ck it up it might be fun to take a crack myself, buy a used engine for a couple hundred, strip it, clean is up a bit, fit new rods then I would just pay them a few hours labour to switch in the new motor and tune it.

What are the bare minimum parts I need (including any tools I may not have, I got a torque wrench a range of typical tools you'd find in your average home and would buy an engine stand too) to get new rods in. Keen to keep it cheap short of using crap Chinese ebay stuff.

Appreciate any advice or guides too. Cheers!

borka

iTrader: (1)

You need

rods of your choice
Mazda oem head gasket. If running coolant reroute, then 1999 gasket, no reroute 2001 gasket
all oem seals,
New bearings, I run acl race, king bearings is also good
New piston rings, I'm using Mahle rings
Rtv sealant for oil pan

Machine shop stuff
Strip to bare block, have machine shop inspect/measure clearances. If all good, then you can use std size bearings.
Have them clean the block, and hone the cylinders.

Assemble.

I did exactly this, and running 309hp for 2 years now, zero issues.

I also suggest to swap in oem pistons out of a NA 1.8, they are lower compression, good for boost.

bobchiba

Thanks for this - very helpful. Could you explain why I need new rings? With regards to having machining work done, is this an absolute must-have? My concept of this was to change as little as possible and really just slip the new rods and bearings in (so to speak). Would I not be able to get away with just cleaning up the mounting surface on the block & head? Also is lowering the comp rate that beneficial or is it more of an additional bit of safety. Again, these are all assumptions on my part, I am NO expert. Any insight on this stuff would be great. Thanks.

borka

iTrader: (1)

Technically, people have opened up the engines and slipped in rods only and touched nothing else.
some had success, some started burning oil, so I've heard.

Hone, rings, bearings are cheap, so why not do it while in there and have fresh stuff and not 200,000 km stuff.

As you go higher in boost, on pump gas, lower compression let's you have more advanced timing which yields more power. Or if not pushed, gives you more margin for knock, bad gas, sloppy tuning, etc...

Used NA Pistons are cheap.

My block is a 94, with 94 pistons, ebay rods, acl bearings, mahle rings, oem gaskets. And a stock vvt head

bobchiba

okay that all makes sense. I fear machining costs over here won't be that cheap unfortunately but something I can look into for sure. I will always run on 97-98 RON fuel here in the UK, but sounds like switching in oem non VVT pistons sounds like it would take no more effort so perhaps a no brainer. Again, very helpful thanks.

borka

iTrader: (1)

There's really no machining, if the block is good with no scoring to cylinders or bearings.

Honing The cylinders is cheap anywhere.
hot tank the block (clean)
clean the mating surface yourself or have machine shop do it.

My machine shop bill was under $200.

My whole block build was about $700.

WigglingWaffles

Head studs might be a good add-on if you can swing your budget for them.

bobchiba

are those to help avoid any head/gasket leaks from occurring?

SpartanSV

I had to have my crankshaft ground but otherwise skipped the machine shop. I bought a ball hone and honed the cylinders myself.

I kept the original stock head bolts which have been torqued at least 4 times now.

Cxracer

iTrader: (6)

How do you determine the right clearance on your rod bearings? I guess at the point you are going to fully strip the block you should replace all the bearings. But I still don’t get how to determine the bearing dimensions when ordering because you already have to have the bearings in hand if you are going to use plastigauge. Also, it seems plastigauge would only tell you if your new parts are out of spec.

Is this why it is imperative that you bring your crank and block to a machinist to get those dimensions?

LeoNA

If your crank is standard or has not been ground then you need std bearings. The crank journal is measured and the housing bore with bearings installed is measured then the two dimensions are subtracted to yield the clearance. Which should be about .002”.

Plastigage is a rudimentary way to check the same.

The housing bore should also be measured without the bearings to check the bearing crush. The bore diameters are published in the manuals and bearing mfg catalogs. There are + & - .025mm (.001”) bearing sets as well. These can be used if more or less clearance is needed. One +- shell can be used with a std shell if half of the additional +- change is needed.

Cxracer

iTrader: (6)

That all makes sense but means you want to order the bearings after you have stripped down the block and have it measured.

I have also read about increasing the clearance over stock because as you double or triple the power you need to start with more oil clearance because at higher temps and stresses the parts expand more and reduce clearance under load.

LeoNA

Yes, buy bearings after inspecting your bottom end. I have purchased many sets of bearings before hand and ended up buying more or different brands after the fact. .002" is a good starting point.