K8 Build (1.8L V6)

Evening All

I'm in the process of stripping down a Mazda K8 1.8L V6 for a rebuild and installation in a Maita based kit car. The goal for this engine is to keep it naturally aspirated, keep it 1.8L and get some more hp out of it. I've heard a few on the web and they sound great, probably better if it's possible to get a few more than stock rpm.

I should point out I'm a bit of a Noob when it comes to engine building, having only played with the top end of a new Chev 350 for a Jet Boat previously.

There is a real lack of info around on this engine, so I would greatly appreciate any input. With my limited knowledge from digging around on a few forums, I'm thinking to get it to rev happily and semi-reliably it needs: -Upgraded Pistons and Rods -Custom Intake -Dry Sump Kit -ECU

Here are a few pics of my assistant (Sam) and the engine making it's way into smaller parts. The block had "K8 273313" and "CBB BBB HHGA" stamped on it, if that means anything to anyone.

So now the questions....

Is it worth sending the block off to have the cylinder bores machined? Not to gain displacement, but to make sure they're perfect for when I put it back together? Can someone point me to an option for Pistons & Rods? I noticed that the Piston & Rod need to be put in from the top because the casting wouldn't allow them to be inserted from the bottom. Does this limit the options for rods?

I'd say there are two ways forward-Whole hog, or basic refresh. Lots of grey area in between. Can you see the factory crosshatching on the cylinder walls? If so, I'd say just a simple honing would be a good bet.

To be a bit more scientific, you need to measure the cylinder bores. Machine shops can do this, but you're kind of giving the fox keys to the hen house if you trust them to determine yea or neigh on a bore. How many miles were on this engine? It is not unusual for an engine of this vintage to be okay with just a hone, new rings, a crank polish, and new bearings.

I'd just send the heads to the machine shop with the crank. They'll clean and check everything.

This is a neat project. Tons of character. I look forward to pictures of the car this will power. You are definitely on the path less traveled.

I'm also fairly noob when it comes to engine rebuilds, and I can report that I've really enjoyed investing in some precision measuring tools and a manufacturer's repair manual. Once all the parts are out and clean, (with care taken to note the original placement/order) I was able to begin careful measurements, and careful note taking.

The factory manual makes this so much easier because it gives you step-by-step instructions and tolerances for all the parts, like pistons, cylinder bores, wrist pins, wrist pin bores, etc. You'll need a telescoping gauge set and a few different sizes of precision micrometer. I found some YouTube videos about measuring engine internals and watched a dozen or so the help separate the wheat from the chaff (free advice being worth what you pay for it and all.)

In my case, it's looking like a hone and re-ring will be fine, and I feel really proud of having seized the reins, taken the mystery out of it, and done it myself.

As far as the stampings on the block, I'm guessing a serial number and perhaps a factory bearing fit guide? Not to familiar with Mazda, but I've seen other Japanese engines where the main crank bearings come in three sizes, A, B, and C, and the factory measures the bottom end when new and stamps the block.

What are you basing your statement about needing pistons and rods on? In general your weak link trying to spin an engine faster is that it won't make power there without a ton of work. I'm going to ignore that issue with this motor because i don't think that's the case seeing as how the 2.5L version still seems happy at high6's, 7000rpm. Next thing is usually rods. They can hit metal fatigue and let go in short order trying to decelerate the pistons from higher speeds in shorter times. It's not an immediate thing but how long it would take gets drastically shorter the higher you spin. Then you have valvetrain issues. If the spring is not strong enough to return the valve to the seat as quickly as the cam lobe is pulling away from the follower/bucket/lifter/whatever, all the parts between the valve stem and the cam lobe can 'catch air' and then smash together with durability consequences. The piston can also make its way to TDC faster than the valves are retreating and actually hit and bend the valves if it is an interference engine.

So, you basically need to try to find as much anecdotal evidence as possible of whether anyone EVER suffers stock rod failures or experiences valve float and its attendant consequences at whatever rpm you're shooting for. I'm assuming 9k or less?

This sounds very interesting as these engines have always intrigued me. Keep us posted!

So I had a pretty hard conversation with the local engine shop. They're telling me for them to build this from scratch I'm looking at US$11k. The rebore and skim for the cylinder block is $500 so I'll start with this.

They're quoting $2k for pistons and $2k for rods.

The rebore is +0.5mm from stock, so pistons at 75.5mm? Anyone seen this size off the shelf?

That's absurd. Custom forged pistons are generally way under $200/ea. For off-the-shelf applications it's sometimes under $100/per.

That's a "Please go away" quote. Don't take that seriously.

There is loads of info on the mazda KL series engines on Probetalk.com/Mx6.com Before you commit your wallet to something, food for thought, you can get a KLZE 2.5L from various JDM engine importers, essentially same block from an exterior standpoint, higher compression and about 200hp out of the box. All that, for about $700 if you shop wisely. They are essentially bolt in with some small tweaks (maybe sensors, intake manifolds etc, not entirely sure since I've never owned one myself) on any application you can use the 1.8. Also become a member of the Probe/mx6/626 groups on Facebook, always people selling rods, pistons etc from bulk buys of the past.

Sending this off for a skim and a cylinder bore next week, but I've hit a snag....

How do I remove this bush and pin protruding from the block?