How to PROPERLY rebuild a 7mgte by KMP

[karlou426hemi]

First of all, all information provided in this thread comes from my personal experience with the 7m and other various engines i have worked with in my life. All the tricks, custom mods and all the assumptions i'll make are for ME, the best way to properly rebuild a 7m engine. I don't expect everyone to agree with me but please don't just discredit what I will say because you've read something else on the internet. Instead try to think twice before questioning and try to properly understand my point of view because i'm sure it will make sense.



let's talk a little bit about the project goals...
I am rebuilding this engine to put it in my girlfriend supra since she spun a bearing past novembre a week before putting the car away for winter. The engine had a 57trim CT26 installed with a lexus AFM and was boosting 18psi on the stock ECU with an SAFC; well pretty much the worse setup to have if you like your car running instead of broken. The new engine will be rebuilt using 99% stock components (except valve springs) and it should develop around 550-575whp as it is the max output of the turbo i'll use on it (EFR7670). (This turbo was on my 1JZ vvti MK3 last summer and dynoed 577whp with it so this is why I know what will be the output of the motor). I decided to rebuild the 7m instead of swaping a jz because I strongly believe that is is a lot more cost effective to do so.


Where to start when modding a 7m..

Even for just upping the boost the first mod to do is to put a PROPER engine management unit. it can be an AEM V1, V2, infinity, pro efi, MS3 MS3pro(this is what i use)...obviously the EMS need to be tuned by a competent tuner to ensure that it will be reliable. Even for the slight mods you still NEED an EMS if you care about your engine. Piggybacks will work for sure but it WILL eventually fail.. My .02 here is if you don't have money to install an EMS, why not just forget about having a modded supra. Most of the time 7m's fail because of the owner, and it happens more often than the famous 2jz because everyone who can't afford a jz or an MK4 end up with a 7mgte MK3 and as they have no money and they want 1000hp, they make stupid upgrades and bandaids to make there car fast, or at least, fast for the time it will work.

Now let's talk about the engine itself. I think i don't even have to mention anything about the head gasket problems of the 7m. Let just say that a proper MLS with studs will cure the problem forever if done properly. The stock internals of the engine DON'T need to be replaced for any setup on pump as it is impossible to put down enough trq on pump to bend a rod a a properly tuned setup. It is the same for the pistons, if detonation is kept away and the tune is spot on they will never fail on you on sub 650-700whp power levels. Many have done a rebuild and preferred to replace the rods and pistons instead of spending there money at the machine shop for a properly clearanced engine. This is not the way to do it!!!!!!

The WORST thing about the 7m is the OILING SYSTEM. Take care of it by modifying it the way it should and it will put the average 7m beside the 2jz as far as 500whp level reliability.. that 's what ill discuss in my next post...

FOR more info about all my projects, like my FB page
https://www.facebook.com/KMPsystems

 

[Nick M]

I decided to rebuild the 7m instead of swaping a jz because I strongly believe that is is a lot more cost effective to do so.

Absolutely. You already have a core unless you overheated the engine with a plugged radiator and low on coolant from old age leaks.

The WORST thing about the 7m is the OILING SYSTEM. Take care of it by modifying it the way it should and it will put the average 7m beside the 2jz as far as 500whp level reliability.. that 's what ill discuss in my next post...

I don't think so. The head and block being dissimilar metals is the real problem. Many manufactures do it and just try to control temps.

 

[JDMMA70]

I don't think so. The head and block being dissimilar metals is the real problem. Many manufactures do it and just try to control temps.

agreed, granted the engine block is an old design, I still find it impressive that they managed to still find use for and make it work some 20+ years later.

 

[jetjock]

Of course your point of view makes sense to you but that doesn't mean it's technically correct. That said:

1) The proper way to rebuild the engine (except HG torque) is by following the service manual. That generally applies even when modifying.

2) The comment about needing aftermarket engine management for slight mods is nonsense.

3) Other than cooler size and how it works there's nothing wrong with the oil system.

 

[thesupragod]

3) Other than cooler size and how it works there's nothing wrong with the oil system.

Not sure that i totally agree with that last statement... Something about a pressure based system isnt quite right. Replacing the entire filter block with a remote mount and a thermostatically controlled cooler is light years better than a pressure based system. Why would you need to cool 40* oil on a cold startup?

 

[jetjock]

Agreed. What I meant by "how it works".

 

[karlou426hemi]

Ok i don't agree with all the previous comments but that's not the point....

I'll start by explaining how a properly set up oil system work in an engine.
Every engine is designed to work around a certain FIXED pressure of oil going through it. All internal clearances are set to work with a certain grade of oil and a SET pressure. Most of the time this pressure is around 90 psi, obviously every car don't maintain this fixed pressure at every RPM, pressure nearly always go down significantly at idle and sets, most of the time, between 30 and 50 psi. In every oiling system pressure goes up quite fast with rpm because internal clearances stay the same so as the pump accelerates pressure goes up. Now nearly any engines (including th JZs') reach around 90 psi of oil pressure at somewhere between 2200-2700 rpm, after that the oil pump bypass valve opens and bypass the excess oil to keep a fixedpressure. Now if you remember i said that an engine was designed to operated at a fixed 90 psi of oil pressure, but have less than that from idle to around 2500. Well this is not very important because engines rarely have their full torque bellow 2500 and they are rarely putted into heavy load bellow this point. (this is assumptions for an engine with a red line around 6-7k, obviously, engine with lower redlines like 4-5k tends to have full oil pressure way lower like between 1500 and 2000 rpm because the have more chances to operate in the 2-3k range).

Another very important factor in the oil system is oil temp.
Oil is designed to operate in a certain range of temp (180f-200f best) Going to low witch seems a good idea to raise oil pressure especially on the 7m will never let moisture evaporate from the oil, and having more and more water in the oil isn't really good. Going to high, the other way around and what happen most of the time on the stock 7m, will keep moisture out off the oil, but oil will be thinner witch will raise the maximum RPM needed to reach full oil pressure (not good) and the oil will degrade faster witch means that it will need to be changed more frequently. So the best oil system is one that let the oil reach it's operating temp as fast as possible and succeed at maintaining the temps in the 180f-200f range in every conditions from light load cruise to high rpm high load pull.

Let's see how the 7m oiling system works



1. oil is picked up by the pick up tube in the pan (1)

2. oil is pumped by the oil pump, pressure rises with rpm and when pressure reach 90 psi full pressure is reached and oil pump bypass valve opens to bypass excess oil. There are some people who says that shimming the bypass spring will raise oil pressure at idle, this is STUPID. the bypass valve cylinder seal around the cylindrical section of the piston so there is no oil that can pass around it until the cracking pressure (90psi) is reach. even is the piston start to move toward the opening ( shown on top of the diagram), there is no pressure loss at all, so shimming the spring will give noting. I also measured the spring for coil bind and toyota did a great job choosing it as it coil bind as soon as the piston reach the end of the hole to relief the oil pressure, witch means that any size of shim will limit the flow capacity of the bypass by blocking it witch can result in oil pressure going to high at high rpm

3. oil then goes to the oil filter housing where it can pass through the oil filter or if oil pressure reach around 50-60psi the oil cooler valve opens to let oil flow through the cooler and back to the pan. This is the FIRST MAIN problem with the 7mgte oiling system. If the cooler valve open at 50-60 psi it does 2 supid things, it makes oil very long to heat up because when cold oil pressure is high and the oil always flow through the cooler. the second thing is it prevent the engine from reaching it SUPPOSED operating oil pressure. If toyota used an oil pump bypass valve opening pressure of 90 psi, it is because the engine is made to run with 90psi of oil pressure. instead on the stock system, maximum oil pressure is limited to 50-60 psi to let the ability to the oil cooler bypass valve to cool the oil.

4.then the next step is the oil squirters. there is a ball valve in the squirter bolt that is designed to keep all the available pressure at low engine speed going to the bearings. these ball valves crack open at around 60 PSI. just a hair above the oil cooler bypass (witch is another reasons to ditch the stock oil cooler because it prevents the oil squirter valves from opening at low to mid engine speed). these ball valves are perfectly fine if the oil pump supply enough oil volume witch i'll discuss later so there is no reasons to touch them.

5. Finally the idle oil pressure and max oil pressure RPM is dictated by the relationship between all internal engine clearances (act as a choke before oil get back to the pan) and the oil volume delivered by the pump. I personnally do not suggest building an engine too "tight" to help with low speed oil pressure.

this how i tested the cracking pressure of every valves : (did the same with oil cooler and oil squirter, I just didn't film it)
i putted oil in my tube, so it better replicates on engine function



[video=youtube;d47UOTK0ELU]https://www.youtube.com/watch?v=d47UOTK0ELU[/video]


how to cure oiling system problems

There is two main modifications to do to the oiling system to make it REALLY up to the task.

1. Replace the stock oil cooler with something better, honestly running no cooler at all is years better than keeping the stock one in place.
you now have 2 options, run a oil cooler that uses coolant (like on the 2JZ) or run an external cooler WITH A THERMOSTATIC VALVE.
the first one will need you to put new coolant hoses and is probably the most cost effective solution. the drawback is that is stresses more the coolant systems and can lead to overheat on a very hot day on high power applications. For under 400whp THIS IS THE BEST SOLUTION
the other solution is to use an external oil cooler that will make oil pass through it and by in the system instead of taking oil volume and put it bac in the sump.
It is MANDATORY to use install a thermostatic bypass valve to allow oil to bypass the cooler when cold to help it reach it's operating temp quickly. the thermostatic valve will also ensure that the oil stays in the 180 -200f range instead off just being too cold on cold weather because all oil pass through the cooler at all times.

here's a diagram of the oil system i made for my stock block 550whp build.
I use a mishimoto sandwich plate with a thermostatic valve with an eBay 30 row oil cooler. I also have a fan on the cooler that turn on is oil temp goes higher than 200f
As you can see in this diagram, there is no pressure loss by the oil cooler, oil is just redirected in the cooler as it become to hot




The second mod to to is to cure the low oil pressure at idle and the full oil pressure RPM that is way too high on the 7m by booting the oil pump output.
the mod is pretty simple and requires very few parts. the ONLY way to REALLY boost the oil pump volume is to overdrive it. the stock pump has a drive ration of around 2.75 times slower than crank speed. this is way to slow and THIS IS THE MAIN REASONS WHY OIL PRESSURE IS SO LOW AT IDLE. so to boost the oil volume produced by the pump we simply replace the stock pulley that drives it with a smaller one. the best match i found is a mazda protege 1.5 or 1.6 cam gear. it has nearly the same width and has 36 tooth instead of the stock 46 witch will boost the output volume by around 30%. You just need to find the gear witch should be available in any scrapyard and bring it with the original to any machine shop and say that you want to keep the external part of the protege gear with the center part of the OEM one and that the new gear must be "on center" with the original oil pump drive gear. the 2 parts can be bolted or welded but this is not the best material for welding, it works but doesn't like to be heated very much. But it works as mine is welded.





Look how smaller the pulley look!!



Obviously the original timing belt no longer works because it will be too long with the smaller pulley. I calculated that you need to remove 2 theet of the belt so instead of the original 159 tooth belt you need a 157 tooth belt witch is ridiculously easy to find....
Just tap 1256-8m-25 on google and by it from any of your favorite site. 1256 is the length (8 x 157), 8m is the distance between theet and 25 is the width.

Don't worry, this mod will not overspeed the pump at high RPM. the drive ratio is now around 2:1 so it puts the put at camshaft rotation speed witch is half the speed of every other engines that have a crank mounted pump....

I strongly believe that this SHOULD BE THE FIRST MOD DONE to the oil system, way before the oil cooler replacement because it will take care of the low idle pressure and I am sure it will cure the cam journals scoring problem...

My final advice would be to run the proper viscosity oil.
Since you can now have a descent oil pressure please run a 10w30 or 10w40 oil grade, not something like 20w50 because with the tight bearing clearance in the 7m, a too thick oil will prevent oil from having a good flow out on the bearings on cold start and will not lube them properly. So stick with the recommended oil grade by toyota, witch was chosen according to the internal clearances of the engine. And it is strongly advised to run only synthetic oil (except for break in) on a turbo engine, not really for the engine but more for the turbo that operate a a much higher temp.

Oil change should also be pretty frequent as the engine only contains around 4L of oil compared to 6L for the JZs. so if you'd change the oil on a 5000KM interval with a 500whp 2jz, change yours at 3000- 3500 on the 7m

 

[karlou426hemi]

Forgot to mention,

The beauty of all these mods is that they can be done in place on a properly working engine, there's no need to remove or rebuild your engine if it is working well. It's nearly just like installing bolt ons.....

 

[hvyman]

There is no reason to switch to a 10 anything oil. 5w or 0w works and flows the best.

and stock spec for oil pressure is 4.3psi at hot idle. the oil pressure is not low.

also prolly the most overlooked item in any build on a 7m is old oil squirter bolts which im not sure if you posted about.

and adding washers to the pump to increase pressure is a lit simpler and safer than modding an old cast pot metal pulley.

 

[karlou426hemi]

i think you need to read my post again with what you are stating.

 

[Suprazz]

wow great information. I agree with what you say and everything is measured and well thought

 

[Nick M]

The oil circuit is also listed in the factory manual.

 

[JDMMA70]

4.3psi or 0.3 kg/cm^2 is the minimum spec allowed.

New or healthy 7Ms generate around 1 kg/cm^2 or 14.2psi at idle. At 3000rpms its 36-71psi or 2.5-5.0kg/cm^2.

Likewise the minimum spec allowed for 2JZ engines are 0.5 kg/cm^2 or 7.1psi at idle (Health 2JZ engines produce more than this at idle, just like 7Ms). At 3000 or 4000 rpms its 47-84psi or 3.3-5.9 kg/cm^2.

Pressures generated by these two engines are quite similar.

 

[Rollus]

Haters gonna hate.

Thank you for the write up Karlou.

BTW you forgot some details, as mentionned
I have changed oil squirters when I rebuilt my engine. Old ones were probably leaking, and it is cheap insurance.
There is also a big pressure waste by a used CT26. The CT26 is the reason why we can see little to no oil pressure at idle. With cooler relief valve already blocked of, I gain 1kg/cm² blocking the turbo oil cooling lines. I guess I will have a separate oiling system on my next turbo.

 

[Backlash2032]

I 100% agree with rollus. Using a stock, worn out CT26, my oil pressure on the stock gauge would sit around 0 at idle. Verified with a mechanical gauge it was 10 psi... Rebuilt it, and now its floating around the first mark on the stock gauge. I haven't checked it with a mechanical gauge, but i'm willing to bet its around 20 psi...

 

[karlou426hemi]

obviously worn out turbo bearings can be a factor for low idle oil pressure. i was just putting the turbo bearing clearances in the the same category as engine internal clearances as it is the same

i'll make a big update tomorrow

 

[karlou426hemi]

I'll now talk about engine rebuild and what to ask from your machinist...

Mandatory steps:

Face head
Face block (don't forget the timing cover when facing the block)

Both of these steps are very important in proper head gasket sealing, and should be done with a very very very smooth finish. You should not be able to feel the machining marks passing your fingernail on the block !!! when facing the head remove the minimum from it. For the block, i'll explain later....

Have the whole rotating assembly balanced!!!! (no the factory 7m is NOT a well balanced engine)

Unless you really don't push your engine (and by that i mean you don't really often go past 5k RPM and don't run more than 300 BHP), a balancing job is one of the more important things to do. Some will say that the 7m run smooth and is a well balanced engine but if it runs pretty smooth inside the car it is because it is an inline 6, not because it is well balanced. Just take a ride in a car with a 1jz or 2jz and hold the shifter, you"ll know what i mean especially at high revs. When I had mine balanced my machinist was shocked at how much material he had to remove from every components... that tells a lot.
I also had personal bad experiences with 7m engine balance back in the days. I was exploding pressure plates in the 7.5k range...snaping every rivets holding the 3 straps. After 3 pressure plates i found that they were not breaking when engaging the clutch but when it was released, weird... Ended up balancing the rotating assembly and never had another failure revving to 8k...

balanced rods:





Suggested rebuild steps:

these steps are not mandatory IF YOUR ENGINE IS IN VERY GOOD SHAPE

oversize with new pistons (please don't cheap out putting new ring with a honing job...do an oversize and run as new pistons to wall clearances)
Machine crank mains and rod journals
Valve job


Clearances you want:

A lot of people with tell you to build it tight, the tighter the better if you want your engine to last long...
What I say is respect OEM clearances, shoot for the center of the clearances.. building it tight is just a band aid to help the undriven oil pump, witch should already be corrected

Block decking.
here there is a rule to respect. you want to end up with a piston to head clearance between .035 - .040. For exemple, my head gasket thickness was measured like that:
3 layers : .007,.031,.007 (.045 total)
so to have a piston to head clearance of .040 pistons had to stand out of the block .005 at TDC.
so remove enough material to respect this pistons to head clearance.
Yes it will bump your compression a bit, but the engine will become more resistant to detonation.. please don't slap an as thick head gasket as you can on it because "the lower the compression the more boost you can run", it will totally fuck the squish in the combustion chamber and will reduce a lot the engine ability to resist detonation. even if you end up with 9:1 (witch is impossible) you'll still be able to run 22-26 psi on pump... (I run 22 psi on my dad's miata daily for a while on 91 oct and it is a 10:1 engine so if your engine fail because of detonation, don't blame the compression ratio, it is because your tuner can't tune a damn engine!!!!!)






Head:

I personnaly recommend to NOT leave the cams and the cam journals scored, this is stupid. remove the scoring marks from the journals in the head and have your cams smoothed by your machinist.
If cleaning your head journals and cams make you exceed the acceptable tolerance then your head is fucked and replace it. do it now, a used head could be found very cheap so just replaced now as you are into the rebuild.






Personnaly I recommend doing a small porting job, especially if you plan to run cams or shoot for 400 bhp or more.
what i recommend is to smooth the transition at the valve seat as the 7m head castings seem pretty rough in that area and can have a shoulder of more than 1/8" in that area.




I also removed the aluminium between intake and exhaust valves as is have no squats effect at all and can become a hot spot in the combustion chamber
also always smooth the edge of the combustion chamber an the fresh machined head




Replacing valve springs is mandatory also if you plan on boosting over 14psi or revving over 6500.. Sure the oem ones will go there but the power will go down. On a lot of 7m dyno graph the power falls very rapidly after around 6200. this is the sign of valves that start to float. replacing springs give a lot more pleasant over revving capabiity and BC springs or BBC inner springs don't cost that much.

BBC inner springs vs OEM



Finnally, always use assembly lube when rebuilding your engine, not engine oil. And don't forget to clean the oil passages by removing the hex plugs as they are nearly always full of dirt.
Also is is a good idea to clean all the threads for the main and head bolts to ensure proper torque values

 

[karlou426hemi]

Forging or not forging ??

Personnaly I think that forging a 7m should only be reserved for people who drag races with an upgraded transmission as a h400 or something like that..

OEM rod are know to handle 600-625WTQ and the stock pistons will never die if kept out of detonation.
OEM BLANCED rotating assembly is totally up to the task even rod bolts up to 7700-8000 RPM because even if the 7m has a big 3mm more stroke LOL, the RS ration is as good as on the 2jz and the pistons and rods weight is down by nearly 100g vs the 2jz witch are known to handle 8500 RPM on stock bottom ends.

Now think about it, a 7m is mated to an r154 witch is known to fail at around the 700wtq mark.... Personally I find the 600-625 wtq limit of the 7m a fucking good match with the transmission !! What it means is that even if you upgrade everything, you'll only be able to gain around 75wtq on the stock tranny and that will be pushing it to it's limit...

Plus a stock bottom end 7m don't need to have a power band that fall on its face at 5500-6000 limiting the max whp to a matching 600whp/600wtq. Just making it hold its torque curve flat to around 7500 would get you this....

600wtq x 7500RPM / 5250 = 857whp... now find me someone who really need more than 800whp on the street plus 850whp at 7500 will make the transmission happier than at 650whp at 5200

And YES I am saying that 800WHP could be obtained out of a stock bottom end 7M !!!!!

 

[Nick M]

All internal clearances are set to work with a certain grade of oil and a SET pressure.

I almost forgot to say at certain temperatures.

Another very important factor in the oil system is oil temp.
Oil is designed to operate in a certain range of temp (180f-200f best) Going to low witch seems a good idea to raise oil pressure especially on the 7m will never let moisture evaporate from the oil, and having more and more water in the oil isn't really good. Going to high, the other way around and what happen most of the time on the stock 7m, will keep moisture out off the oil, but oil will be thinner witch will raise the maximum RPM needed to reach full oil pressure (not good) and the oil will degrade faster witch means that it will need to be changed more frequently. So the best oil system is one that let the oil reach it's operating temp as fast as possible and succeed at maintaining the temps in the 180f-200f range in every conditions from light load cruise to high rpm high load pull.

You certainly put time into this, but this tells me you lack information about desired characteristics of oil. The manufacturers go for flow, not pressure. Temperature affects it. Low temps increase resistance of the oil to flow and it shows up as higher pressure. Your conclusion is correct. Get the oil to 200 degrees as fast as possible so it will flow correctly and the additive pack will do its work.

 

[Rollus]

Pressure and flow are intimately linked