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240Z Aftermarket Itm Pistons Issues

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Hello,

 

My engine builder has just informed me that after mounting my pistons, ITM brand, item number RY2516-030, they are protruding above the deck of the block. The top of the P30 block was decked with about 5-7 thou removed, so that is not the problem.

 

They measured the piston height to the old ones that came out before mounting (a slight difference of 5 thou) and after mounting them on the rod bolts and into the cylinder, they protrude about 30 thou above the block,

 

Does any one have a theory as to why this would happen.

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Is the crank offset ground or from a different engine to give more stroke?

 

Are the same rods used?

 

Are the correct sized rod and main bearings used?

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Is the crank offset ground or from a different engine to give more stroke?

 

Are the same rods used?

 

Are the correct sized rod and main bearings used?

 

The crank was from the original engine to my knowledge. The original connecting rods were used and were not replaced.

 

They did remove 10 thou off the crank, and thus inserted the Clevite Undersized Rod and Main bearings if that tells you anything.

 

I have read that some of the stroker engine guys use two head gaskets instead of one, but there has to be another answer.

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Hello,

 

My engine builder has just informed me that after mounting my pistons, ITM brand, item number RY2516-030, they are protruding above the deck of the block. The top of the P30 block was decked with about 5-7 thou removed, so that is not the problem.

 

They measured the piston height to the old ones that came out before mounting (a slight difference of 5 thou) and after mounting them on the rod bolts and into the cylinder, they protrude about 30 thou above the block,

 

Does any one have a theory as to why this would happen.

Which is old and which is ITM?  You don't really say which is which.

 

There's much written about L28's and piston pop-up of about .022" but I can't find much on L24's.  BRAAP measured a bunch of L28's with flat-tops.  Post #19.

 

http://forums.hybridz.org/topic/58127-best-way-to-achieve-piston-to-head-clearance/

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Which is old and which is ITM?  You don't really say which is which.

 

There's much written about L28's and piston pop-up of about .022" but I can't find much on L24's.  BRAAP measured a bunch of L28's with flat-tops.  Post #19.

 

http://forums.hybridz.org/topic/58127-best-way-to-achieve-piston-to-head-clearance/

 

The ITM pistons were ever so slightly taller when they were both placed on the same wrist pin together for measurement.

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Sounds right to me. You should be fine.

5-7 thousands-couldn't be more specific than that?

Now this is where the HG really gets important. What's the crushed thickness of your selected HG?

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Sounds right to me. You should be fine.

5-7 thousands-couldn't be more specific than that?

Now this is where the HG really gets important. What's the crushed thickness of your selected HG?

 

Hi Steve,

 

I think I am going to go with the FelPro gasket, not sure of thickness.

 

I think I might need a head gasket between my left and right lobes of my brain!

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The ITM pistons were ever so slightly taller when they were both placed on the same wrist pin together for measurement.

That is ever so much clearer.  Kidding.  Kind of.  Seriously, you need numbers.

 

Really though, your engine builder should be familiar with this and know how to deal with it if he's experienced with the engines.  Nissan pistons are all essentially the same except for flat-top versus dished.  Did he say it was a problem or just mention it in passing?

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That is ever so much clearer.  Kidding.  Kind of.  Seriously, you need numbers.

 

Really though, your engine builder should be familiar with this and know how to deal with it if he's experienced with the engines.  Nissan pistons are all essentially the same except for flat-top versus dished.  Did he say it was a problem or just mention it in passing?

 

No, he was disenchanted and frustrated, with no answer except to machine the top of the pistons. Not something that should be done in my mind.

 

I have seen a few threads where the piston and valves were on a collision course, it can't be good.

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No, he was right pissed off and frustrated, with no answer except to machine the top of the pistons. Not something that should be done in my mind.

 

I have seen a few threads where the piston and valves were on a collision course, it can't be good.

Disturbing.  Their web catalog of services says that they work on 81-83 L28's, which all have a pop-up of ~.020".  He shouldn't have been surprised and should have compared to the old pistons right away.  Not really clear what the problem is.  If the new ITM's are just a hair off the old, what's to be right pissed off about?

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OMG-don't let him machine those pistons.

That's what i ran on my L24(deck height), and was fine. It's a bit tight with a 1.25mm HG, but that's probably what the Felpro is.

Like stated, most of these engines run about 22 thou deck height(what I have read from numerous posts). Then you shaved off 5-7 thou off the deck, so there you are with about .019 piston the head clearance.

The only way to know is to measure. I bought two felpro HG's just for that reason. I am going to find out exactly the crushed height of the felpro.

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Disturbing.  Their web catalog of services says that they work on 81-83 L28's, which all have a pop-up of ~.020".  He shouldn't have been surprised and should have compared to the old pistons right away.  Not really clear what the problem is.  If the new ITM's are just a hair off the old, what's to be right pissed off about?

 

Agreed! He did say that the difference of 7 thou was no big deal either, but why the difference once installed?

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OMG-don't let him machine those pistons.

That's what i ran on my L24(deck height), and was fine. It's a bit tight with a 1.25mm HG, but that's probably what the Felpro is.

Like stated, most of these engines run about 22 thou deck height(what I have read from numerous posts). Then you shaved off 5-7 thou off the deck, so there you are with about .019 piston the head clearance.

The only way to know is to measure. I bought two felpro HG's just for that reason. I am going to find out exactly the crushed height of the felpro.

 

Steve. Very insightful bit of information, I'll get some exact numbers on the positive deck height.

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Hi Guys, here are the numbers on the Block Thickness. The block measured originally at 10.469" and now measures 10.45857".

 

The engine builder is looking into the availability of steel head shims to bring the head up and away from the pistons.

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After speaking to Dave at Robello Racing (good guy), he suggested there be at least a 35 thou piston to head clearance with the head gasket compressed.

 

For racing purposes, he did not recommend the head shims, but for daily driver use he said they would be OK.

 

When I mentioned about turning the pistons down on a lathe, he said he has done 100's of pistons this way.

 

He instead recommended a Cometic Head Gasket at about 56 thou in thickness (factory head gasket at 45 thou) in height (Cometic sells them in varying heights) $$$$

 

He also told me that many guys are running the F54 block with P90 Head with the pistons at about a 20 over deck height with no problems.

 

If my math is correct the pistons are currently sticking out about 18-20 thou.

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Not to pick on your builder but he could mock things up with your old gasket, or no gasket and some math, and some clay or soldering wire, and actually measure the clearance.  Most of us get disturbed because we don't have the experience or the tools but this should not be a big deal.  If he came to you and said "the new pistons are only .015" from the head and that's a problem" that would make sense since there are general guidelines/thoughts on that clearance.  But the consternation over .007", right off the bat, seems odd.  Either you're not getting the complete message or he's getting disturbed over something he shouldn't be.  Anyway, it's all part of the game.

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This story actually runs a little deeper. Initially I had purchased the ITM RY6335-030 pistons (the ones with the valve reliefs).

 

The engine builders installed them about two weeks ago only to find out that they were too tall and protruding through the top of the block also.

 

When I phoned ITM's reseller here in Canada, he promptly phoned ITM and had the Sales Manager at ITM, measure both the RY6335 and the RY2516 on the same wrist pin.

 

He actually showed images of the two types of pistons having a difference in height by about 30 thou (RY2516-030 being slightly shorter). I have to locate his images to show you.

 

So, I ordered the RY2516-030 pistons thinking well this is the cure as the piston height of the RY2516-030 is correct and was going to be a slam dunk.

 

ITM and their supplier in Canada would not allow me to return them, instead offering me a set of 6 at cost plus free shipping.

 

So it is with great surprise that these new RY2616-030 (the ones with NO valve reliefs) are protruding also.

 

Maybe I am not being told the whole story, I am not sure, but I can tell you that there is a difference between the RY6335 and the RY2516 pistons.

 

I am going to leave the decisions up to the builder as to a solution, and see what he recommends. I build websites for a living not engines.

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Is my math off or does it add up to .011 that he shaved off the block. If so, then he has cut it to tight and you will have to do something different.

My block I figured 22 out of the hole and another 5 off the deck gave me 22 clearance. The more you read about deck height though, the more number you get. But even at the small side of 19 out the hole, you would have 30 total leaving 19 clearance--IF my math is right..

 

...and if my math is right, then shame on the builder unless it took that much to clean up the deck and he had no choice.  

 

How much cam off the head?

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Disappointing being that my car has the matching numbered block, if that were the case.

 

Removing block material in a Datsun engine is never a good idea as I have understood.

 

He has stated that he just skimmed the top, and no more than .007". I have faith he is telling me the truth.

 

He did ask me if the block was ever rebuilt before though, but I can't trace any history past 1987 when I first purchased the vehicle.

 

I can tell you that the pistons that came out of the engine were Standard Size and not overbored.

 

There is much to be learned about Deck Clearance in the book "How to Modify Datsun 510 610 240Z Engines & Chassis" (pages 125-126).

 

It is stated in the book that you can have as much as .020 positive deck height, provided your run a thicker gasket such as a Cometic Head Gasket that is .060" thick compressed.

 

So simple math would suggest that if I have + .020" piston out of the hole, and add the Nissan's preferred Deck Clearance of .035", then that would add up to .055".

 

Having said that the Cometic Head Gasket is .060 thick. This would provide the necessary deck clearance I so desire. Is my math correct?

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No, he was right pissed off and frustrated, with no answer except to machine the top of the pistons. Not something that should be done in my mind.

 

I have seen a few threads where the piston and valves were on a collision course, it can't be good.

Dave Rebello told me that this can be a problem with ITM and that machining the top of the piston is the solution.

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Wow, I have quickly become to listen to what Dave Rebello suggests, so good to hear.

 

Perhaps I need to have the tops turned down so i can get back to 0 deck height. This way I could use a stock head gasket.

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Dave Rebello told me that this can be a problem with ITM and that machining the top of the piston is the solution.

I had the same problem using Nissan .040 over L24 ( 73 ) Pistons with the valve reliefs. We were .030 out with a stock height block. We milled .020 off the Pistons ........I think it cost $100.00. Problem solved!

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When I advised ITM's Sales Manager of the difference in height, I thought they would have offered a better deal than just a replacement set at cost.

 

Hardly standing behind your product, but when it comes to pistons, there just isn't many options out there. At least there is a simple solution to all of this.

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I had the pistons turned down 0.020" and now enjoy zero deck height.

 

Now I can run a stock head gasket, part number 11044-N4221. Pickup the block and and head on Saturday from the engine builders.

 

Thanks to all who contributed, I hope others can gain what I learned from this thread.

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