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Let's talk N9T** head issues...

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From Facebook:

Let's talk n9t/e/ea head failures, did they get better or worse since 1984? Has anyone actually narrowed down the actual cause of cracking? Also has anyone ever replicated the head? Hopefully using a better alloy? If so has that head cracked in the same location?

I also recall someone mentioning that the danielson head might have had the same cracking issue?

Is the cracking due to insufficient cooling? Or the wrong combination of metals? Or a bit of both? Material thickness? Poorly designed chambers?

Anyone here own or know of a cyl head shop that could do some testing?

How often do the heads crack again after a welding job?

Could we make a group effort to help these engines live longer and with a ton more boost? (Yes I know the driveline wont last, splines and all) Maybe do some of our own R&D?

If it so happens that the head would crack due to the materials used, maybe it's just simple as having it replicated with a different alloy?

I plan on rebuilding my motor in the yellow car, or possibly swapping in another n9te I have out of an auto wagon which had just been redone before pulled. I need to drive this yellow 505 again it runs however has developed a rod knock, it's been too long, and I need more boost, let's do this.

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I am definitely interested in this topic, as I am 99% certain that my car’s head has given up the ghost.

Tom

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Some answers to the questions on FB:

Closed deck:  Sounds like someone has Subaru experience in their past.  :)  Not only is it a closed deck design, but it's an iron block so the block is very stout.

Head crack history:  Likely more due to the era this engine was built as even Toyota had head cracking issues.  MANY other car makers including BMW's have the exact same issue with cracked heads - but no one really makes a fuss as they're fixable for reasonable money just like N9T** heads.

Head crack causes:  Some say it's due to a common practice during that era of press fitting valve seats with too much interference. Over time it caused the crack from the seat to the water jacket.  Others claim poor cooling systems.  

My theory:  I've studied this for damn near 20 years and I think it's poor cooling circulation system design.  As soon as the closed system is compromised the head vulnerable to air pockets which causes temperature differentials in the head.  The reservoir HAS to be completely above the head, and the head, engine, and rad NEED to be able to self bleed themselves of air.  I've got a ton of ideas on how to fix this - I just have lacked the time to document and test on my own engines.

Head fixes:  This is a relatively easy fix, with known good shops providing great repairs.  If there was enough interest I'm sure we could organize a group buy on head repairs, I'd even be happy to approach them for costing if we had 5 or so ready to put down cash.

Overall I think the N9TE has crazy potential and is seriously overlooked.  Biggest issue is the limited capabilities of the ECU, and I'm sure if these had a well tuned standalone (+ injectors) you could throw quite a bit more at this engine even with the stock bottom end.  Throw in forged pistons and lighter forged rods and I see no reason why these wouldn't be 300 RWHP cars.

Rabin

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Danielson head:  These are subject to the same head cracking as the OE heads.  My understanding is that they got the same head castings, but that they were machined slightly differently.  I see no signs of welding and re-machining - so if that was done it was done really well.  Combustion chamber is shaped different, and the spark plug was changed to a different angle entry, as well as a smaller 10mm race plug design (same as a sport bike).

Rabin

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The best way to have new heads cast is probably to made them JRD style so that they can also be machined for dual plugs and used in historic race cars.

You should ask Marcel Morel about that: http://www.maurelec.fr/

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Thanks SRDT!  I've seen his twin plug heads as well, but we'd need to collaborate on the specifics so that heads here could be fixed and  machined for the second plug.  Firing two plugs would be easy with standalone as you could simply use a v8 coil pack or 4x wasted spark coil packs.

I've got a couple wrecked heads I could use for R&D, but finding someone to do the machining would be tough.

Rabin

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You can also use a Nissan 720 distributor cap for a period correct look.

And for the existing heads why not beryllium copper valve seats, with this you can hope to spread the heat away from the cracking zone.

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Agreed on the beryllium copper seats - When I had done the research on the probability of the valve seats being too tight, those were the recommended seats to use.  5 angle valve job on intake, stock 3 angle on the exhaust.

As for the cap - If one is going through all this work to modify the N9T** a standalone ECU really is a must, so hopefully a distributor wouldn't be in the scope of this project. 

Rabin

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I am not an expert by any stretch of the imagination.  I remember someone saying that the n9 has an iron block with an aluminum head. The concern was the different rates of expansion between the two metals.

i remember reading the owner’s manual cover to cover from my first (83 505 STI), and it said to never race a cold engine.  The turbos have an oil temperature gauge, and it does take considerable time / miles for it to get up to temp.

i see way too many folks jump in the car and do burn outs and such.  Dumb.

Bill

 

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I like this discussion, and want to say from the start i don't have any direct experience with this engine but have some with POCH tuned lada race engine which supposedly is an n9te engine. Mechanics that worked on those engines are still around here and have told stories on how tight and robust they are, also that the head resembles more a alfa romeo twin cam head then the factory peugeot head. i've seen an Lada Poch (simca JRD) head of the block and it has hemispheric cambers and staggered valves very similar like peugeot used on the TU engines but much bigger and twin spark plugs if i remember right. In my opinion to get the right answer, why do they crack you must strap an engine on a dyno and use a thermal camera and see how the coolant behaves under loads i'm sure there is same hot spots, some mods like polishing the combustion chambers enlarging some of the coolant pass edges and using waterless coolant will fix this problem but some one needs to spent the time to figure this out.

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Sadly those kinds of dyno services aren't available, and at $150+/hr in the bigger cities it's just not feasible to do it in Canada unless you have very deep pockets!

Bill: Very good point - Part of the driver to go to a proper standalone ECU Is it can limit boost based on engine temp - Once the car is properly up to temp - then it can be set up to increase boost.

They also usually have WBO2 oxygen sensors, and ideally an EGT sensor so that fueling the motor is so much morr accurate. 

Rabin

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18 hours ago, Bean said:

As for the cap - If one is going through all this work to modify the N9T** a standalone ECU really is a must, so hopefully a distributor wouldn't be in the scope of this project. 

Rabin

The cap can do on a N/A Matra Murena, to be Murena friendly you also need those two mounting bosses:

culass2.jpg

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Goce - A while back I did some research on the Lada POCH race cars.  Engines weren't turbocharged,  but they were built NA Maurolec engines that were rated at 240HP, and then later they used the ROC version of the engine with their DOHC 4 valve head on a 2.5L version of this motor making 280HP.

Funny enough they then went to the PRV V6 after that.

http://lada-poch.e-monsite.com

I'd LOVE to find the ROC head for these engines, but the cams would be all wrong for boost.  :)

If you're ever able to meet and ask about how they twin plugged the head I'd definitely be open to modifying my heads as well.

240HP out of an I4 SOHC 8v on carbs is very impressive - especially in offroad endurance racing.

Rabin

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13 hours ago, Bean said:

Goce - A while back I did some research on the Lada POCH race cars.  Engines weren't turbocharged,  but they were built NA Maurolec engines that were rated at 240HP, and then later they used the ROC version of the engine with their DOHC 4 valve head on a 2.5L version of this motor making 280HP.

Funny enough they then went to the PRV V6 after that.

http://lada-poch.e-monsite.com

I'd LOVE to find the ROC head for these engines, but the cams would be all wrong for boost.  :)

If you're ever able to meet and ask about how they twin plugged the head I'd definitely be open to modifying my heads as well.

240HP out of an I4 SOHC 8v on carbs is very impressive - especially in offroad endurance racing.

Rabin

I'll ask around but is very unlikely someone keep an good spare head, evan then they were on tight budgets. As for the twin spark plugs, those heads had a different casting and the spark plugs wore on the side of the head, one next to the inlet port other next to the exhaust port, but i've seen guys modified fiat heads with drilling straight into the combustion chamber and welding in a solid piece thet thay letter drill countersink and thread for little spark plugs. That is an involved process but is not that hard, last year or so i've been involved more heavily with machining and there are much harder things done just to fix cylinder heads then modifying one.

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Finally getting into the garage again and couldn't resist tearing into a parts motor that I got that was seized.  Figured ot was good for the odd rare parts, but the head has only started to crack - Kicker is that it's starting at the water jacket!

Both 2 & 3 are just starting to crack - neither has made it to the valve seats.  Should be an easy fix.

Also looked at dual plugging and it would just need way to much work to do properly.  I think the Dani relocation using the existing spark plug hole is the way to go.  Better plug location, better plugs, and better coils should be plenty of improvement and pretty much negate dual plugging.

Will definitely save this head and will likely look at getting it fixed/rebuilt if someone needs a head. (I've already got 2 Dani heads and a known good head).

Rabin

1532411875078-310132302.jpg

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Sorry a little late to this conversation.

When my head let go many of the cracks also were originating from the water jackets.  Leading me to believe that the technology is just a little too old or bleeding edge for the day to function properly 30 years forward.

I truly admire you for trying to go bigger on HP. 

My car is finally coming together, but I'm really at a crossroads.  Parts availability in general is killing my desire to keep the car.  If the engine lets go, maybe a swap.

These cars are like Jay Leno's strange orphan cars that can only survive and thrive with his resources.  Like Anj's Porsche brake swap to deal with the unobtanium rotors, keeping some of the original Peugeot stuff is getting harder and harder.  Especially if you're going to be breaking parts.  And if you ain't breaking parts, you ain't trying hard enough to go faster.

This kindda squirrels away from the original question you posed.  I plan on using the current best practices for keeping my head alive as long as possible.  I, unfortunately don't have anything else to offer.

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About n9t (9n2 and other same family) head problem. N.A heads suffered same issue but on n9t it has more heat load on exhaust side. And due N.A design there is narrow edges on exhaust valve seat and water hole, other problem is casting material (aluminum) and air bubbles and residues. This info is coming from welder who has welded over 10000 alu heads for repair. But once its repaired properly it will hold (seen only one n9t head with crack on welded one). Sodium valve was not solving problem thats why it was stop used in n9te (86 ->) models and it was costly valve.

I must bit disagree about parts availability, depends how to look it. Surely parts not found every corner shop and there is rare parts. But so far there is no part which can not be found for engine or car. It could take time and effort but usually these are not daily drives any more, I have seen many younger cars having way worse parts problem even cars made after 2000.   

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