JCH13 - Turbo Miata Rehab Thread

[JCH13]

So, last Friday I exploded the engine in my Miata. Well... that might be a bit of an exaggeration. I lost power and found that there was a catastrophic amount of blow-by. I had to go out of town for the weekend, which was torture with my car all sad and 'sploded, but I got to work first thing Monday night.

Leakdown numbers on 1-4 were: 4, 36, 7, 40; with lots of air coming out of the crank case. Yup, that's new engine time.

I tore the engine and transmission out and took the engine apart down to the short block and this is what I found:

A little errosion and a crack in piston #4, I attribute this damage to the fact that this engine had 240k miles on it when I dropped it in two years ago.

The cylinder bores in #2 and #4 were both pristine:

So, with all good guts in the engine, I'm thinking rebuild time! I have been pricing out connecting rods and pistons, likely going to go 'forged' on the bottom end to not worry about power anymore.

In the meantime I arranged to buy a used 80k mile driveline for $425, so I'll have that to drop in and drive around with while I build my serial racecar engine.

On a related note, my clutch was almost worn out completely, so time for a new clutch too.

Edit: finally uploaded some pictures from an autox last year:

 

[jlee]

Forged internals, E85 and 26psi? :awe:

 

[JCH13]

Forged internals, E85 and 26psi? :awe:

NH still isn't on the E85 plan. :'(

Also I don't want a calendar to quantify spool-up. :awe:

 

[jlee]

NH still isn't on the E85 plan. :'(

Also I don't want a calendar to quantify spool-up. :awe:

Heh I think you need a ride in my car.

 

[exdeath]

Heh I think you need a ride in my car.

Do they even make calendars in half second increments?

 

[JCH13]

Heh I think you need a ride in my car.

You have turbo cams AND way more liter-pony-torques than I ever will.

Besides, the transmission will start to get iffy at power levels much higher...

 

[exdeath]

Turbo snail sez fuk ur pistons.

 

[JCH13]

Lots of work over the weekend. The new/used replacement engine was in decent shape, but not good enough to just drop in, unfortunately. Initial leakdown numbers, and leakage location, were:

1-13% blow by
2-7% exhaust valve
3-20% exhaust valve
4-12% blow by

After a bit of massaging (nominally letting stuff soak in seafoam overnight) I got:

1-5% blow by
2-8% exhaust valve
3-25% exhaust valve
4-3% blow by

Other clues:
-Oil in plug wells (valve cover gasket clearly never replaced)
-Spark plugs caked black in carbon
-Tons of carbon build-up in exhaust ports

Conclusion: car was running like shit, lots of carbon deposits caked onto everything. Adding seafoam probably freed up the rings a bit, and partly (but not entirely) cleaned off the exhaust valves and seats, causing extra leakage.

Action: disassemble engine head. Clean head, lap valves, reassemble.

Engine on engine stand. The chain fall is making life really not suck right now. With it I can do everything by myself.

Miata drivetrains have exploded across my garage. It's a disaster.

Three blocks, two heads, dressing for two engines, an extra front and rear subframe (I'm welding up a rear subframe for a guy's V8 conversion), and lots of other crap.

Taking the head apart I found numerous jammed/clogged HLAs. A common issue with Miatas. I'll take them apart and clean them.

Everything apart and soaking in ATF to clean off the immense amount of carbon buildup (way worse than the engine that came out). Learned how to use a valve spring compressor, made pretty quick work of it all things said and done.

The bottom end looks good. No scoring, decent hatching, smooth movements with no detectable slop. I poured oil on top of each cylinder to prevent rust and to give the rings even more opportunity to free up.

Hopefully tonight I'll be able to clean out the ports and valves and maybe be able to lap the valves. Any tips or advice on lapping?

I ordered new valve guide seals (because why not?) so reassembly will be a little delayed. I could reassemble the block and transmission (when the parts for that arrives) and drop that into the car if I'm still waiting on the head, but I'd rather do it all at once if possible.

 

[JCH13]

Took a break from rebuilding the head for my engine to start welding up the sub-frame differential brackets for a guy doing a V8 swap.

 

[FuzzyDunlop]

these are great updates! Lots of work.

Did you have to upgrade your ceiling beams at all for that engine hoist? Im REALLY curious about this.

EDIT: Whatcha got there?

 

[JCH13]

these are great updates! Lots of work.

Did you have to upgrade your ceiling beams at all for that engine hoist? Im REALLY curious about this.

EDIT: Whatcha got there?

Thanks! Also re-read your valve lapping thread, great info there.

The PO did all of that installation, actually. I believe that the floor joists are 2x10s with a couple load-spreading 2x10 or 2x12s laid out flat across the tops of the joists. Nothing too super-serial. Apparently he pulled a dump body off of a truck with it... something I would never attempt!

I think that's a bottle of root beer, as boring as that sounds. A friend of mine, who helps me frequently, loves the stuff. My ethanol alternative of choice of late has been Allagash Curieux.

 

[JCH13]

I could not get satisfactory results (to my standards anyway) by hand-lapping valves. I dropped the head off at an engine machining shop yesterday with a guy who has done a bunch of spec Miata work (hooray experts!) and quoted $90-$165 to hot-tank and cut/grinding seats/valves depending on how many intake valves needed it after checking all of them. All of the exhaust valves will get done, the ones I had trouble sealing. From what I can tell that is a super-reasonable price for a '3-angle' valve job.

 

[JCH13]

Got the head back. The shop decided to do a single-angle valve job, noting that there's not enough room to make a 3-angle job worth it. Final cost: $100 for hot tank, cutting all valve seats, grinding all of the valves, and a quick lap to make sure everything is concentric.

Shit, I wish I had known there were shops this inexpensive earlier...

 

[jlee]

Cheep!

It's always nice to find a good/reliable/affordable machine shop...

 

[FuzzyDunlop]

wow ya. thats very affordable.

 

[JCH13]

Washed off some/most of the gunk from the new engine and transmission

Picking up flywheel later today from being resurfaced.

Getting close... will have more pictures soon.

 

[JCH13]

Brace for big update.

Got the head back from the engine shop after a valve job and steam cleaning:

In prepping the head and the block for a new head gasket I was reading up on how people clean off the gasket surfaces. I didn't like a lot of what I read. Many people suggested using sandpaper, scotchbrite, and other abrasives. The thought of even a small bit of those abrasives getting into the oil sump gave me nightmares. So, after a bit of thought, I decided to use a razor blade to clean off any large chunks of old gasket, and steel wool with a little bit of ATF to clean off everything else. Steel is not going to be the most abrasive material in the engine (especially non-hardened steel in steel wool) and it will be collected by the drain plug magnet if it does get into the engine.

I then bolted the head back onto the block using a new HG and the stock head bolts. I ran up the torque in 4 steps. First, finger tight, then 20ft-lbs, 40ft-lbs, and finally 60ft-lbs. With AMSOIL assembly oil on every surface it went together without any issues at all.

Then I began re-assembling the engine.

Cams, HLAs, and a new water pump.

Rear main seal installed with a FM rear main installer tool.

At this point I decided to make a custom part for the coolant re-route modification. The reroute deletes the front thermostat housing, which also contains the fan switch sender. So, I made a plate that mounts the fan switch directly to the block, where the thermostat neck used to be. Right here:

As I went about making the part on my CNC router I realized that no gasket exists that will work for this. At least none that I knew of. So, I sandwiched some gasket stock behind the aluminum I made the plate out of.

And cut out a gasket at the same time the plate was cut. Hooray! Here is the plate (tapped and w/ counter-sink for an o-ring), gasket (before cleaning it up a little), new o-ring, and fan switch sender. I smoothed the plate's surfaces with 100grit sandpaper in a DA sander.

I got liberal with the RTV when installing it, I was a little worried about leaks. Here is the plate installed with the cam pulleys, FM cam pulley tool, timing belt, crank timing pulley, and FM crank pulley tool all on the engine.

With all of the front timing bits, covers, pulleys, etc installed, time for an adult beverage! The handy FM pulley tool has a bottle opener built in. Genius.

Continuing to dress the engine...

 

[JCH13]

Resurfaced 1.8L flywheel with new pilot bearing.

I put the engine on my overhead chain hoist and mounted the clutch, new throwout bearing, and the transmission after it got new front oil seals and a new tailshaft seal.

Intake on...

Turbo and manifold on...

Dropping the engine and transmission back into the car.

I used a bit of belt welding wire (SS) sandwiched under an extra bolt head to keep the fan switch wire clear of the timing belt.

I re-did my oil cooler setup to use a narrower, taller, core mounted behind the coolant radiator and in front of a much slimmer fan. I like this setup a lot more than my previous setup, which was nearly inaccessible without removing body work.

I also installed R4-S brake pads and flushed the brake lines. This handy little device that I assembled made life awesome. It regulates my shop air to ~3psi and applies that to the brake reservoir, making flushing the brake system a snap. I did all four sets of pads and flushed the whole system in around an hour by myself, including adjusting the e-brake.

Other details that aren't captured in picture form: I installed frog arm chassis braces, used AMSOIL MTL in the transmission, filled the cooling system with just distilled water (I am planning on flushing it in a week or two), filled up with 4.5qts of 5W30 synthetic engine oil (planning on changing oil and filter as soon as the clutch is broken in, using 5w-40 AMSOIL synthetic), and finished the coolant re-route with all home-made parts aside from the Cadillac radiator hose.

Engine fired first crank!

Last night I took the car for a test drive. No leaks of any sort (holy crap!), fans kicked on with the temp gauge just below the half-way point, and everything seems to be working as intended. *phew*

 

[jlee]

woot!

 

[JCH13]

Per suggestions from several other Miata drivers and after a bit of research I decided to try a disconnected rear sway bar. Holy grips batman! The amount of rear-end grip available on-throttle during corner exit is staggering. I should have done this years ago.

 

[FuzzyDunlop]

why is that? allows the inside tire to remain planted instead of lifting?

Hows the oversteer now?

 

[ballmode]

nice!

 

[JCH13]

why is that? allows the inside tire to remain planted instead of lifting?

Hows the oversteer now?

In a simplistic sense, yes. In a technical sense: sway bars control which axle weight is transferred to, so by removing the rear sway the rear axle sees a much smaller amount of weight transfer, which allows it to have more grip than the front axle.

Oversteer is a lot more controllable and it is much more difficult to lose traction when rolling onto the gas out of a turn. The stability of the car is incredible now.

This success has me thinking about getting a considerably stiffer front sway bar so I can still use a rear bar and benefit from an overall increase in roll stiffness without changing the really nice balance my car has now.

nice!

Thanks!

 

[JCH13]

Coolant leak!

It looks like my coolant re-route hose started to loosen where it connects to the rear of the head. Not a big deal since it still only has water in it, and not anti-freeze.

 

[manimal]

Coolant leak!

It looks like my coolant re-route hose started to loosen where it connects to the rear of the head. Not a big deal since it still only has water in it, and not anti-freeze.

Its always something isnt it?


Sorry you melted a piston mang!

everything looks awesome including your shop ! I am back in a small 2 car home garage and I am still a sad panda. I can at least look at cars again which yours always makes me smile!

Next year sometime I plan to do a miata once my vette is gone.


wish all the epic build threads were in a sticky at the top!