[dA_RoB]

Hi guys,

As I have heard a lot of discussions on this topic and there seems to be a lots of different meanings I would like to hear what the engine builders on here have to say.
Now, I know that the guys at Tomei use this dummyhead but there are as well a lots of guys who don't.

This for example I got from an local machine shop which does a lots of JZ engines:
"better let a lil more tolerance gap and make a good patient break in than bore the engine with a head on it

an EVO block with L19 ARP does an issue and then you need the dummy but no RB or JZ needs it"

In the german sky forum a guy measured the bore and after taking the dummyhead off and it made 0.03mm difference.

Thanks guys!

Cheers,
RoB

 

[Conrad]

Use a torque plate torqued up to the same as the head would be if it was on.

 

[dA_RoB]

I would like to know more. What's the theory behind and so on...

 

[dA_RoB]

Noone had thoughts about this and would like to discuss this?
I really would love to hear the theories and facts from the forum known engine builders as well

Cheers!

 

[Rain]

I've also heard the same. About the blocks not needing a torque plate for the RB.

What I've heard is unless the engine will be a very close tolerance build. The RB doe not flex enough to need it. Being cast iron and fairly rigid to being with. I know some builder here have done before and after measurements would love to know more.

I've also heard that to utilise a plate correctly you should be getting the block up to running temp as well. Dunno if outside of Motorsport applications this is a very feasible endeavour?

 

[Asim R32GTR]

It all depends on your goal.

If you are bulding a high power / torque engine I would reccomend doing the stress honing. Specially if you are using aftermarket bolts / studs. They have a lot more clampingforce then the stock bolts, and will make the bore out of round, more then the stock bolts.

The theory behind it is, that when the head is torqued the cylinder gets out of round (oval). So to eliminate this they put on a tourqe plate. What it does is simulate the same stress as the head will put on the engineblock.

The cylinders are then honed with the stress plate on, and it makes the cylinderbore more exact.

Take a look at this, and you will understand more.

https://www.youtube.com/watch?v=BV_Z6gkRM0Q

I have done this to all the engines i have buildt through the years. I think the guys at Abbey do the same on all the engines they build also.

And also RIPS do the same thing??

Asim

 

[Rain]

Also keep in mind this is pretty much the only way to build an engine with an ALU. Block its really surprised me how out of round they can get!

As far as the 26 goes. No idea why some do and some dont. I guess its dependent on your builder.

 

[dA_RoB]

The thing that makes me very suspicious about all of this is the Service manual.

It's clearly stated that the cylinder inside diameter is inspected without the head dummy. Also the tolerances which are given are as well without the head dummy.
However, if I take a look at the video posted above, after taking off the dummy, there is a out-of-round change of (according to him) 0.0127mm.
Now, if You achieve the same figures on an rb26 after taking off the dummy, it would mean that You're just close to the out-of-round limit. What if I achieve a figure which is higher than the limit stated in the manual? Therefore, is the out of-round-limit mentioned in the service manual valid with the head on the block or without it?

I have understood what You guys are telling me and for me it is clear that there are differences between the method with and without the head dummy, but what confuses me is also stated in the post.

I hope I described it accurate enough for everyone to understand! If no, please tell me

Cheers and thanks!

 

[FRRACER]

How many people use this method in the UK apart from Abbey we know about? If you were to do something do it properly, there must be a reason why Tomei do it amongst other Tuners in Japan and I do not believe those who say it is only needed on a aluminium block.

 

[Asim R32GTR]

It is definetly not only for aluminium blocks. It goes for all engines.

It all depends on what type of fastener you are using, the more clamping force, the more out of round the cylinder will get.

 

[FRRACER]

Well I would be using ARP or Tomei studs.

 

[Asim R32GTR]

The thing that makes me very suspicious about all of this is the Service manual.

It's clearly stated that the cylinder inside diameter is inspected without the head dummy. Also the tolerances which are given are as well without the head dummy.
However, if I take a look at the video posted above, after taking off the dummy, there is a out-of-round change of (according to him) 0.0127mm.
Now, if You achieve the same figures on an rb26 after taking off the dummy, it would mean that You're just close to the out-of-round limit. What if I achieve a figure which is higher than the limit stated in the manual? Therefore, is the out of-round-limit mentioned in the service manual valid with the head on the block or without it?

I have understood what You guys are telling me and for me it is clear that there are differences between the method with and without the head dummy, but what confuses me is also stated in the post.

I hope I described it accurate enough for everyone to understand! If no, please tell me

Cheers and thanks!

The servicemanual was not made for 600 / 800 / 1000 + + hp engines....

 

[FRRACER]

Also keep in mind this is pretty much the only way to build an engine with an ALU. Block its really surprised me how out of round they can get!

As far as the 26 goes. No idea why some do and some dont. I guess its dependent on your builder.

Maybe that's why some engines fail and some don't and why some engines can run stock crank and std block as make a lot of power?

 

[dA_RoB]

Had a talk with an engine builder last saturday and he gave me a very impressive example by telling me that his 1000hp 2JZ was done without the dummyhead and held a lots of 1/4mile and street driving until one of the conrods went broken.

so, I guess both methods work if everything is done correctly. the most important thing according to him is the correct break in phase and procedure. he didn't tell me what it was but I'll find out

And, only because tomei is doing this with this plate, it really doesn't mean anything. I know they are professionals but sometimes you have to critically question stuff!

Cheers!

 

[FRRACER]

If you take your engine to a local engineering firm they would not use a dummy head, the engine build I am sure will be good, but not at the same level of tolerance and detail that a Tomei or a Mines engine would be for example.

Many quality tuners in Japan do however use this method and those who do are anal about quality, precision and perfection and is reflected not only in the price but the reliability or their end product.

 

[Asim R32GTR]

Had a talk with an engine builder last saturday and he gave me a very impressive example by telling me that his 1000hp 2JZ was done without the dummyhead and held a lots of 1/4mile and street driving until one of the conrods went broken.

so, I guess both methods work if everything is done correctly. the most important thing according to him is the correct break in phase and procedure. he didn't tell me what it was but I'll find out

And, only because tomei is doing this with this plate, it really doesn't mean anything. I know they are professionals but sometimes you have to critically question stuff!

Cheers!

Ofcourse both methods work... Did you think the engine fails if not stress honed?

Its all about keeping the compretion inside cylinder and above the piston. The more leakage, the more blowby and in extreme conditions loss of hp... which furthermore affects the tune of the engine.

Like I said earlier, it all depends on your goal.

You can ask 100 different engine builders, and you will get 50 different answers.

 

[R32 Combat]

I cannot see an aluminium 'torque plate' having enough strength to twist a cast iron block. In fact, I can only see it comounding the issue.
Lets assume the torque plate IS stiffer than the block and can twist it, the torque plate must be flat to within a few micron. If it is not, then any error will be transmitted into the block and twist it.
Does anyone agree?
Also, the bores need to be perpendicular to the crank, thats where you should set up from rather than the head.

 

[Asim R32GTR]

I cannot see an aluminium 'torque plate' having enough strength to twist a cast iron block. In fact, I can only see it comounding the issue.
Lets assume the torque plate IS stiffer than the block and can twist it, the torque plate must be flat to within a few micron. If it is not, then any error will be transmitted into the block and twist it.
Does anyone agree?
Also, the bores need to be perpendicular to the crank, thats where you should set up from rather than the head.

You are supposed to use a headgasket when using the torque plate. And the head stud / bolts you are using.

It isnt a thin plate, it is probably half the thickness of the head.

This isnt a new thing... its been done like this for centurys, and is properly documented on why it should be done. Do a simple google search and you will find lots of machine shops that use it. Some of them take it one step further and heat up the engine block to operating temps while honing the cylinders.

 

[R32 Combat]

You are never going to be able to simulate bore wall flex due to combustion pressure. That is the biggest influence on distortion.
My point is still valid, if your torque plate and head have different torsional strength and flatness is different, you are not going to get the desired results.
It's certainly a good reason to charge customers more money for reboring. Other than that I personally have no faith it's adding value to the process. You would be better spending money resin coating the inside of the block to stop microscopic bits of iron and sand entering the oil.

 

[Rich_A]

Has anybody had one of these made?

I have a contact I might ask. I suspect the billet alone would be expensive.



(*That picture of the Tomei one is excellent. If Tomei do it, I want one, my experience with their quality is excellent!)