Low Compression - How Long Do I Have? What Motor to Get?
 

Hello RX8Club,
I am a Miata guy but with the birth of my first son last October I needed a "family car" , so I decided on an RX-8.

I bought an 6spd 04 GT for a decent price on Saturday, but it has the typical hot start issue where it will take ~3 revs before it starts when hot. I decided to get the compression tested to make sure it wasn't the battery or the starter and here are my results;

#1 Leading:

229 RPM
#1 = 61 PSI / 4.3
#2 = 58 PSI / 4.1
#3 = 56 PSI / 4.0

#1 Trailing:

241 RPM
#1 = 64 PSI / 4.5
#2 = 60 PSI / 4.2
#3 = 60 PSI / 4.2

#2 Leading:

244 RPM
#1 = 78 PSI / 5.5
#2 = 79 PSI / 5.6
#3 = 82 PSI / 5.8

#2 Trailing:

247 RPM
#1 = 81 PSI / 5.7
#2 = 82 PSI / 5.8
#3 = 84 PSI / 5.9


I don't have a manual but I know that they are way under spec. This prompted a call to the dealer and I was going to return the car(*you have 3 days for an off-site sale in WI) but we ended up settling on a price reduction and I am going to look for a replacement motor for when this one goes.

This leads me to my first question. How long do these motors last when they get this bad? Are we talking a week or two, or maybe a few months?

And secondly, it seems the 2006-2008 motors are much more reliable. Would I be better off with a low mileage 2004 or a higher mileage 2006+ motor? Or should I buy a core and have it rebuilt? I could also get a reman from Mazda for ~$2500(I think 4 port only though)... what do you think would be the best option?

My commute to work is about 4 miles and its just enough time to get it up to temp, and I drive about 4 miles to lunch every day. Would it help to get a turbo timer so I don't short-trip it to death?

I read that its good to do an Italian tune up on rotary's and they like to be driven hard (once they are up to temp). Is there any truth to that? Should I be hitting 7K+ a couple times a day, for good measure? :rock:

Thanks in advance!

Lucky Kid

You probably have less than 10,000 miles before that car won't start at all when hot. You are already well into the point when you have significant blow-by past the seals and it's rapidly degrading at this point.

Since you have a 6sp MT, your engine is a 6-port engine. All 2004-2008 6-port engines are the same design, same flaws. You can't upgrade to the 2009-2012 engine for less than the price of your car. Far too many changes.

The older years had more problems mostly because of the ECU patch-work that was done to try to improve things. A fresh engine in a 2004 chassis has the same chances as a fresh engine in a 2008 chassis, assuming that they have the same ECU flash between them and are otherwise identical in mechanical health.

There are lots of engine replacement options, and the only option that is worse than buying a reman from the dealer is having someone do a seals only rebuild when they don't know what they are doing. Dealer remans are very suspect in quality and more than a couple people have paid for remans on their own dime just to have it DOA, and Mazda doesn't warranty it unless they also install it.

Either go with a used engine with known compression numbers or hunt for a reputible shop to do the rebuild. There are only a handful in the US that I would trust.



As far as new owner tips, take a look at my signature.

Mazda does remans on all of the 2004-2008 engines. list price is $2001, and there is a $100 install gasket set in the box.

Anyone know a good rebuild shop near Milwaukee? I doubt I will find a junkyard motor with compression results, but I may be able to get one with a warranty.

If some remans show up DOA and I am SOL then that won't work for me.

How hard is it to swap these motors?

I've changed about a dozen on miata's but I have no experience on other cars. Is rebuilding a core myself a viable option? I've rebuilt heads before, but never a bottom end.

Thanks,
Lucky Kid

The shops I would trust I can think of off hand are in Atlanta Georgia, Knoxville TN, one in Alabama, a group of 8clubbers in Texas, one in Phoenix, and maybe one in LA. I may be forgetting a shop or two in there.

There are really not very many out there. Well, there are several times this many, but with less than stellar reputations.


Having replaced Miata engines twice and RX-8 engines zero times, I don't have strict experience with the pull process. However I believe the skill required is going to be about the same, with really only some changes to exactly what components you are removing above the engine.

There is no head, and no bottom end, in this engine.

I hope I don't come off as that helpless.

I was more referring to my experience that I know how to make and apply gaskets and use a torque wrench, but I don't have experience with bearings and the like.

Would patience and a so-so mechanical ability allow me to build a solid motor, or does one really need rotary specific experience to build a good one?

Thanks,
Lucky Kid

The short answer is no.

If you skip the "good" part then yes, you may be able to build an engine.
The devil is in the details. Less parts means that each part adds more to the overall outcome of a build.
Clearances, little tweaks, upgrades, mods are what set a good build apart from an average backyard build. Balancing is also crucial if you drive the car very hard.

If your car is a toy then you can play with it as much as you want. If you need your car and it has to be reliable then nope. Save some money and pay an experienced builder to do it absolutely right the first time.

That's a very hard thing to answer. There are only 3 moving parts, another 5 main non-moving ones plus some other smaller bits and all the seals, so from that perspective it's pretty simple. However, the skill ends up being involved proper clearancing of the seals, the stacking of everything when you assemble, knowing when you can reuse something and when you shouldn't, etc...

It's simple to do, but there is a huge difference in the power and lifespan of the engine depending on how good you are at the seal work.

Does this mean that only a few people can do it? Of course not. You might have exactly the mind and skills needed to be able to do it 100% right. (or you might not :) ) Experience plays a big part, but then no one started as an expert.

If you decide to rebuild it yourself, you will give yourself the best shot possible by really reading up on it ahead of time, get a rebuild manual, learn where the critical points are, etc...

i have yet to do an Rx8 engine, but it can't be as hard as a miata.

if you can rebuild a head properly, then you're in good shape to do the engine. the rotary is pretty simple, the problem most people have is trying to reuse parts they shouldn't.

Rebuilding isn't hard as long as you have plenty of time and patience. Go slow, ask any and all questions you have. Do it right and do not short cut anything or cut any corners. Make sure you watch a few videos and if you're still sketched out order a rebuild video from Mazdatrix.

+1. the older engines have a page in the back of the FSM which just lists all the clearances, and i just go down the list and measure everything, and replace as needed, it takes FOREVER, but it takes a lot of the judgement/guess work out too.

you also end up with an engine that's in spec, and actually where it is in spec.

for example, side housing step wear limit is 0.0039", so 0.002 is still good, but its also halfway done

Is it in my best interest to throw ~8oz of pre-mix oil in every time I fill up?

I only got through about 20 pages of the pre-mix thread before I was ready to kill myself.

Thanks,
Lucky Kid

Average would be 0.5oz per gallon, heavy would be 1oz per gallon. Use a JASO FD rated 2 stroke, ecspecially if you are running a stock cat.

You can purchase various rebuild kits that provide all the necessary hardware for a rebuild if you are mechanically minded.

another option is to order a rebuilt engine from the likes of Mazmart or Pettit with improvements over the stock engines for better performance

Mazmart says they don't cover it unless a mazda dealer or shop does the install. I would hate to get a motor with low compression or one that was DOA.

Is there a viable reman option for around 2K that has protection against a DOA/bad compression?

Thanks,
Roy

Not really.


Some here disagree with me, but knowing Paul and how he runs Mazmart, I would have zero concerns about getting a DOA engine from him.

Seriously if you can't swing a few grand for a proper rebuild then this is the wrong car for you. Even if you get a rebuilt engine for $2,000.00, at best you will get a one year warranty and even that will be dependent on who installed it. And with a bare bones rebuild who knows how long it will last under certain conditions. Not to mention that an engine replacement is so much more than just the cost of the rebuilt engine itself. Many, many times old and rotten parts will get broken during the pull and re-installation and you will have to have money to replace that stuff.

You should also replace any wear items (clutch, TO bearing, water pump, belts, radiator hoses, plugs, heater hoses, vacuum lines, CTS, etc.) while you are at it since most shops won't charge you the labor since they would be removing and installing those items anyway. And if you get a proper shop, they should also be cleaning the many items like the VDI, SSV, ESS, etc. that really should be cleaned during an engine rebuild.

All of this extra stuff cost money. And at the end of the day, if you half ass it then you will likely pay way more for that later.

Its not that I can't swing it, its a matter of understanding the market and whats available. I am not in a position to indiscriminately blow 3K on a motor that may or may not work, so I am just trying to do my research. Is the $5100 Atkins build a proper motor, or can I get by with a $3000 MazMart motor? Better yet, is there someone that does a reman using used parts that are well within spec, rather than boarder line, or under spec?

I've seen posts about a $2001 motor but I don't know what or where to get information on it.

I think I will work on a martix of the different builds to better understand whats available.

I will be doing the install myself and I will inspect and clean everything once the motors out if anything is suspect I will replace it. I am not going to spend a few hundred bucks on parts I don't need.

Thanks,
Lucky Kid

Well Atkins doesn't really list what is in (new housings? their rebuilt Renesis and when I called when I was looking they were very vague, short, and seemed annoyed by my barrage of questions. Plus they charge a $1,000.00 core charge that you will not get back if they deem your core as unusable.

As far as I know the Mazmart engines are just OEM remans.

I talked to most of the builders (except drummond and the like)when I was looking and they all vary drastically in their methods and philosophies of Renesis rebuilding. Some say within spec is in within spec so they will use your parts if they are within spec. Some will insist on new hard parts, certain brands of seals, types of seals, coatings, and will have a range of minimum specs they require to reuse stuff and other types of things. Some believe in coating and resurfacing housings and some think it is BS. And some will insist on only OEM stuff only.Others will let you pick and choose what you want regardless of what they recommend but will tell you that you are on your own if something goes wrong.

The $2001.00 engine from Mazda is a bit misleading as some dealers will rape you on the price of parts. But you can get a reman from rosenthal online and have it shipped to a dealer for install if you want the 12,000 miles warranty. In my opinion the only thing a 12,000 warranty insures is that you will be covered should you receive a DOA reman (it has happened to a few I know). But it doesn't cover labor.

At the end of the day it depends on you, your ability, your finances, your plans for the car, your access to a shop, tools, parts, etc. I could have rebuilt my engine and I may next time if I stick with the Renesis but at the time, I decided to let someone who has done a thousand + of them do it. That decision was largely influenced by the fact that I was also doing a turbo kit installation at the same time so I was kind of in over my head at the time since I was replacing many things in addition to the turbo kit and engine.

Remember, even if you get a rebuilt engine or do it yourself you need to realize that there are many hours of cleaning involved and fixing stuff to do it right.

every dealership in the USA sells a reman engine, list price is $2001 plus a $1000 core charge. they come with new gaskets and seals, water pump and thermostat. the flywheel is replaced or resurfaced, and it has an oil pan.

it seems like most come with new rotor housings, but it depends.

I just called my dealer for shits and giggles and was quoted a picked up price of $2700.00 +core.

onlinemazdaparts - $1950 plus core (and shipping).

I know the shop cost/price for the engine is $1600.

Dealer markup varies considerably on everything.

Yep, the guy who installed mine gave me the invoice with it.

I'd call the dealers in your area and see what they offer. They shouldn't be marking it up that much since they are essentially ordering and selling at once.

All depends on the greed factor. Would you believe a dealer that tried charging $10,000 for the engine? The labor was cheap at $6,000 to do the install.

Yes, a Renesis and an RX-8. Only after the owner complained did they "remember" that he was covered under warranty still.