Re-torquing head bolts and gaskets...

The procedure is torquing to 36 ft-lb, then turn 90°, then 45°, in the sequence below.

 

I just looked up the head bolt torque procedure for a 2010 Corolla (essentially the same engine). It said to torque to 52 ft. lbs. and then turn each bolt 90 deg. Wonder why the difference (if there is much of a difference)?

 

If the Corolla uses the 2ZR-FE and the Prius uses the 2ZR-FXE, then any of the engine and head differences related to the different compression and expansion ratios, etc., could have played into the engineers' choices.

 

I thought about this too and think it is a good idea.

Maybe HybridPit can offer that as a service.

 

I haven't even Google this but I want to know what would happen if you put a non Atkinson 2Z Corolla engine up to the prius's business as in its transmission? I guess the regular two Z's going to have too much power and overpower the electric motor generator or something along those lines? That's why they went with the Atkinson cycle detuned 2 z. Is the Corolla the Atkinson cycle 2Z in the hybrid model? I haven't looked been too busy. It's interesting that the Corolla gets higher marks for reliability versus the Gen 3 or 4 Prius.

 

Yeah go for it squeeze down on the head some more half a turn or whatever the heck certainly can't hurt anything nothing's going to break. But I think the damage gets done to the head gasket by high heat from whatever is happening with the EGR starts to damage the gasket no matter how it squeeze down and once that happens well there you go. So it's not a sealing problem and all that. I think it happens before that if you will something gets heated up dealing with that EGR and varying EGR flow and whatever the heck. I mean if you look at the Gen 4 where they added all the shrouds and liners and all this other business this issue is creeping up in that setup too so there you go. But I never had this problem in a regular 2z or 1z for that matter And I've logged near 500K on the two and the one in Corollas had them since they came out and I don't even know 2000 something like that still have my one Z Corolla..

 

You would get diminishing returns. The electric motor is already responsible for creating torque which is the same reason why diesel hybrids dont exist. It wouldnt make much of an extreme difference speed wise nor power, since simply you are handicapped by the transmission and everything has to go through that first before reaching the wheels.
Even other hybrids like fords 2.5L duratec engine also have their cam timing adjusted for their hybrid models.
I think most of it has to do with the rpms needing to be higher since thats what gets most charge. And having less resistance to compress air by keeping the intake valve open longer allows atkinson engines to achieve that. This peaks in efficiency at highway speeds where the engine can directly just maintain wheel speed without needing torque.

Im sure when they first started with the hybrid concept they did use a regular engine and ran into obstacles where it was less or the same fuel efficient at 60mph of running the otto engine through a eCVT vs a regular automatic.

 

I'm sure that's why Honda used a three cylinder in the inside and some iterations or they wouldn't have to choke up the engine to detune it they just built one that didn't have much tune by design if you will kind of like a generator engine.

 

Riffing I'm here looking because I've had a couple jitter on start episodes on my 156K 2012 V. My coolant level (untouched since new) is at about the line on the reservoir or slightly below the low level. I took delivery on a new prime so debating what to do with the V, Wife has continued to drive the "station wagon". Oil use is about a quart in 3K for last 30K
On our old 70-80's Xs650 motorcycle motors we re-torque head bolts as a matter of normal maintenance. Have stopped head gasket oil leaks on many of these motors. I have also stopped severe oil leaks on several high mile modern aluminum 4 cylinder auto engines with a cylinder head re-torque. (Kia and Chevy) These were torque to yield head bolts like nearly all modern engines. The torque to yield bolt is not a modern miracle method, it's a production shortcut. My method is one bolt at a time, loosen then re-torque. If you don't loosen you are not actually tightening just twisting, stretching the bolt.
Can the EGR decoke be done without removing head?

 

Most certainly; see first two links in my signature. On a phone turn it landscape to see signature.

addendum: see the like on “bad flywheel” thread.

 

One thing that is indisputable about gen3 hg fails is the black sealing layer of the metal head gasket erodes away allowing a seep of coolant into the cylinder. For the first few months or even a year it only happens after an overnight cooldown of the engine. Sometimes it causes a misfire; often it does not. The hg seals quickly once the engine is running. At first there are no codes but the shake is unmistakable. The parts cannon is fired. No detectable hydrocarbons in the coolant. No change of compression. No coolant in the oil. No observable coolant reservoir drop. New spark plugs often clear the symptoms for a week or two.

Traditional blown hg causes still apply such as overheat with warping and loose head bolts. But other triggers exist. Some think old coolant eats away at the head gasket sealing layer. Carbon buildup does generate preignition which is quickly detected by the knock sensor but still occurs. Some gen3s get so carboned up the preignition is audible especially when combined with a low hv battery. Aluminum engines warp.

Toyota significantly changed the cylinder cooling passages, head gasket sealing area and cylinder wall heat distribution in gen4s.

 

Disclaimer. I have not done a head bolt re-torque on a Prius, and have not even looked at the procedure (as far as head bolts on a Prius.

That being said, it was fairly common for older BMWs and SAABs (both of which I have had - BMW 2002 and 320i, SAAB 900 and 93).

The problem with simple re-torquing is the bolts are already stretched. I don't know how much of a difference it ACTUALLY made, but it was generally recommended to use new bolts, rather than re-torque the existing bolts (replacing them one at a time).

The theory was that simply re-torquing existing bolts would either not provide the correct final torque value and/or have inconsistent clamping across the bolts because the original threads have been stretched by the torquing process.

 

Yes all the lit calls for bolt replacement everytime you remove a turn til yield bolt. My previous experience on "last legs" cars was retorquing those bolts worked, The engines were head leak free on the way to the junkyard for other failures.

 

Yes all the lit calls for bolt replacement every time you remove a turn til yield bolt.
My previous experience on "last legs" cars was retorquing those bolts worked, The engines were head leak free on the way to the junkyard for other failures.

 

Turning the bolts 10 degrees tighter isn't a re-torque, it's just a common thing DIY mechanics do to see how much more life they can get out of the gasket before swapping it out. It's essentially ensuring all the bolts are tight. While highly unlikely in newer cars, there have been instances in older cars where a couple-few bolts got loose and a quick tightening is a way to get lucky for a little while in terms of avoiding the gasket replacement job.

 

Dummy's back, squeaked by a 1200 mile road trip even though I had a "rattle start" the day before I left, gulp. Can all the head bolts be reached with the cams lifters etc. still in place?
Coolant's now low in the tank,

Bought coolant, filled to low line
honestly I had been looking at the inverter coolant tank,
Sure wish I had known about this when I did plugs at 120K.