Pistons Plus Deck by .7-.9mm... Ideas?

AKimball92

AKimball92

True Classic
This weekend I just installed my new main cap studs with plans to get it line honed this week. While the crank, (old) bearings, and caps were installed I decided to test fit my pistons and check my deck height. I installed the con rods (original) with the new Mondial 8551 pistons in cylinders 1 and 4. The 2 pistons both show plus deck height by .7 to .9 mm depending on location around the pistons. Both were equal with the rear end of each piston (towards trans) being in the .9mm range and the fronts (timing belt side) being in the .7mm range. This is more than I original planned with the guidance from the team here and all my math done using nominal numbers. Note: measurements were taken with a HF 10 dollar set of calipers, but with repeatable measurements.

I had the block decked by the same machinist who did everything else. Unfortunately he did not say how much was removed but I had requested minimum to make smooth. I have ported and polished a 1500 cc Euro Head w/o a decompression ring.

What do you guys think? Is this to much positive deck? Would a particular head gasket fix this issue? I am seeking a .7 to 1.0mm squish/quench clearance.

Also, not sure how the size of the uploaded picture will turn out.
 

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There are head gaskets available with approx 1.8mm thickness (crushing to around 1.65mm) which will get you in your S/Q range., but it will be tight!

machinist must have removed around 0.5mm

SteveC
 
That's the same (essentially) as my wiseco's HERE (.026") The gasket I used is listed in the thread, can't recall now, but pretty sure stock thickness. Contributing factors will be combustion chamber volume, valve sizing, cam (lift? possible inference?) valve lash spec for your cam, etc. Same head as mine? 1500 Euro ("big" valve head)

A8F61DC2-DCE9-4007-8783-16AF57C96FEA_zpsdtittsfa.jpg
 
That is correct Joe. I have a 1500 Euro head which has been enlarged to the 37.5 intake valves. The pistons were machined by SteveC to allow for the large valves. Just to be clear, I am using the 1300 block/crank, but that should be irrelevant for this issue.

Copying SteveC's calculations from this link below but inserting my own numbers into the calculations:
https://xwebforums.com/forum/index.php?threads/melted-piston.22458/page-6

Pi=3.14159
Diameter: 87mm = 43.5mm radius
Plus Deck .9
SQ required=1.9

Every 0.2mm thicker you go in head gasket when crushed is 1.2cc 1.189
(1.195)

Volume of the head gasket.
3.14159 x (43.5 x 43.5) x 1.50
3.14159 x 1892.25 x 1.50
8.917cc
SQ=.6mm

3.14159 x (43.5 x 43.5) x 1.70
3.14159 x 1892.25 x 1.70
10.106cc
SQ=.8mm

3.14159 x (43.5 x 43.5) x 1.90
3.14159 x 1892.25 x 1.90
11.295cc
SQ=1.0

Where do I find a head gasket between 1.7 and 1.9mm crushed? The two gaskets I have will not work. One was provided in a full engine gasket kit from Vicks but has an 86mm diameter but looks high quality. The other is an Guarnitauto gasket of the right size but the water passage holes took a minimalistic approach when it comes to fluid flow. Also, someone on here said that Gaurnitauto gaskets were not the greatest.
Guarnitauto Head Gasket.JPG
 
If it's the same as the 1500 gasket (not familiar with 1300 block) then MWB sells a thicker gasket. Definitely don't use a gasket with a smaller ID than the bore (86mm vs. 87mm)!!!
 
fiatfactory said:
There are head gaskets available with approx 1.8mm thickness (crushing to around 1.65mm) which will get you in your S/Q range., but it will be tight!

machinist must have removed around 0.5mm

SteveC
Click to expand...

Steve,

Where can I find this gasket? I do believe I will need to buy it? I will try to take more measurements and see what I can figure out. I would like for my plus deck to be on the .7mm side and not hte .9mm side obviously.

I heard a lot of good things about the machinist I had but I don't know if I will be going back to him for future work. There were a few things that he did or said that didn't settle with me very well.
 
Okay so I took some more measurements with a straight edge off a little metal ruler I have and my feeler gauges.
Cylinder 1
Front: .53mm
Rear: .73 using sum of .35 +.38

Cylinder 4:
Front: .50mm
Rear: .63mm

The piston in cylinder 1 scares me in that I can feel and see the difference in deck height from front to back. However these numbers are better than .9mm
 
Got pics? Hard to visualize how the piston height can be different front to back, or is it side to side? Either way....
 
By front and rear my coordinate system is in reference to the engine, not the car. Front meaning the pulley or FEAD system and the RHS of the car, and rear being the transmission and the LHS. Standard front engine longitudinal orientation.

Someone else can state which valve is towards the front as I have closed the shop for the night; not sure if it really matters. The tilt in the piston is on the same axis as the gudgeon pin. The deck height on the rear end of piston one by cylinder 2 is .2mm more than the front. The piston slides in nicely into the cylinder. The machinist said that I didn't need to worry about which piston goes in which cylinder. All the piston diameters he measured to be the same and interchangeable between cylinders.

I will disassemble the parts tomorrow and try to take as many measurements as I can.
 
Something is not right...

For the piston to sit lop sided in the same axis as the gudgeon pin indicates a bent conrod, or the small end bush machined off line to 90 degrees of the conrod, or the bore has been machined off axis ... the second issue is the difference from the front of the block to the rear of the block...that indicates the deck is not square to the bore/crank axis.

I recall saying that the method to decking the block surface is to have the block bored, then install pistons 1 and 4 to measure how much you want removed, strip it apart again and back to the machine shop to do the block face...they aren't always square to the crank axis from the factory...

usually you would do the crank tunnel line bore/hone first too... and then use that axis as a datum for all other cuts to ensure the bores are square to the crank, and the head deck is parallel to the crank.

SteveC
 
fiatfactory said:
Something is not right...

For the piston to sit lop sided in the same axis as the gudgeon pin indicates a bent conrod, or the small end bush machined off line to 90 degrees of the conrod, or the bore has been machined off axis ... the second issue is the difference from the front of the block to the rear of the block...that indicates the deck is not square to the bore/crank axis.

I recall saying that the method to decking the block surface is to have the block bored, then install pistons 1 and 4 to measure how much you want removed, strip it apart again and back to the machine shop to do the block face...they aren't always square to the crank axis from the factory...

usually you would do the crank tunnel line bore/hone first too... and then use that axis as a datum for all other cuts to ensure the bores are square to the crank, and the head deck is parallel to the crank.

SteveC
Click to expand...
If the connecting is off in some way then it could be that is the only issue. The deck values seem close from front to back at averaging in the high .55-.60s. It is hard to tell until I am able to sort out the lopsided piston. I will rearrange all the pistons, con-rods, and pins, ensuring each is marked for the correct cylinder. Hopefully that work will be completed tonight, if not then tomorrow night.

As for machining order, I wanted him to skim it minimally first it first to see what I had to work with. If his skim was too deep or the block had already been worked, there is not much I can do now. If the pistons are around the .6mm plus deck range then that is doable if the oversized head gasket is a reliable option.

What tolerances for this is acceptable? Should the pistons all be at .60 +-.03mm, more or less, before any of you would be satisfied with the squareness? I know the tighter the tolerance the better but perfect is impossible.
 
Now I am dealing with 3 variables: Headgasket, con rods, and piston conrod order.

If need be, I can get new Con Rods for $225 from MWB. That is the cheapest I can find online without going "used". That would eliminate those from being at fault. Are there aftermarket forged or lighter con rods for the 120mm range? From my reading of the Ultimate SOHC and other threads that is a negative. I did not plan to purchase new rods in my original build plans.

Could someone please explain the pros and cons and steps taken for the non retorque style head gasket vs the standard (?) retorque style? Everywhere I have read it is suggested to retorque after a few heat cycles and then after 100 miles. Does this still hold true with the "non retorque" style? How does this pair up with torque to yield head bolts vs non vs studs? I honestly need to look and see what I purchased. I know it was an ARP set and believe I went with a stud kit.

Thanks everyone for the help.
 
Still puzzled that you have a height discrepancy- did you use a locating bar to bring the piston up against at TDC? Is it possible the height deviation is simply due to piston rock in the bore? There's bound to be something there, but it never occurred to me to measure for that, and I'm not even sure that would explain it?

IMG_3270_zps364ce23b.jpg


The type of head gasket would dictate retorque or no, ARP studs/nut setup would go either way I believe. True TTY bolts are single use and not designed for retorque
 
The height difference on the piston is measured on the sides associated with both ends of the gudgeon pins, not to either side of the pin which I would associate with piston rock. If that were the case i would definitely install the rings to see if that cleared it up. I just dont see how adding the rings would help with my issue. When looking at your picture above and in the same cylinder you are testing, my low point is "Down and to the left" and my high point is "up and to the right". Unfortunately I did not create the the little bar you have shown. I would need to purchase/find a the metal bar to modify. I could do this at a friends house this weekend.
 
Skip the "bar" or any similar "positive" stop. They are simply not accurate enough for performance engine work. Accuracy to thousands of an inch or 0.01mm is not going to happen using a stop device. Too much slop in threads, flex in the stop and more add up to poor accuracy.

There are plenty of low cost dial indicators on the market. Get one or two, like this one:
http://www.ebay.com/itm/Mitutoto-24...035205?hash=item41c6e90905:g:1fEAAOSwlndZNMnD

The made in China indicators are sort of OK. Given this is a measuring tool, better to spend a bit more and get a known good indicator (Mitutoyo-Japan, Compac-Swiss, Starrett-USA, Mahr-Germany) as they are extremely useful measuring tool.

The other item needed is a dial indicator holder-stand. There are LOTs of low cost magnetic stands that don't work well. Stay away fro these as they cause serious problems to extreme frustration to dropped indicators when least expected.
Good ones are made by Noga.
http://www.ebay.com/itm/252123665052?_trksid=p2060353.m1438.l2649&ssPageName=STRK:MEBIDX:IT

Third item is a accurate degree wheel and pointer that can be mounted to the crank's end on center.

Once this is set up, TDC can be accuracy measured and set.

Height of the piston pop up above the deck of the block should be measured using a depth micrometer or similar.

One other factor to consider:
http://www.motoiq.com/MagazineArticles/ID/1996/Does-Length-Matter.aspx


Bernice
 
AKimball92 said:
Okay so I took some more measurements with a straight edge off a little metal ruler I have and my feeler gauges.
Cylinder 1
Front: .53mm
Rear: .73 using sum of .35 +.38

Cylinder 4:
Front: .50mm
Rear: .63mm

The piston in cylinder 1 scares me in that I can feel and see the difference in deck height from front to back. However these numbers are better than .9mm
Click to expand...

Looking at these numbers again, the piston tilt is much much greater than the difference in pop-up between cyl 1 and 4.
0.2 mm and 0.13 mm difference across the 86mm bore vs. about 0.06 mm (center of piston 1 to center of piston 4) across the whole length between cyl 1 and 4.
So the piston tilt is definitely not caused by machining of the deck non-parallel to the crank axis.
Question: do all 4 pistons sit at a similar angle?

(Side question: 0.06mm diffence in piston pop-up sounds pretty good to me. A number of tolerances add up in this measurement. Wouldn't you call that good?)
 
I would call .06mm from cyl 1 to 4 good in my opinion as well. This is just my first engine build and the tight tolerances are what kept me from breaking into any engine before. That's why I had to ask.

As for the tilt internal to a single piston, I plan to assemble all pistons with correct rods and bearings in the next couple days and deep dive into finding the part at fault for this issue. I will note that I had conrod 3 in cylinder 4, and used an old set of bearings for this measurement. I didn't think that would cause any issue if everything is supposed to be the same. I was just wanting to check deck squareness was all. I will keep everyone posted.

No matter the issue, I at least need to buy a new set conrod bolts, a thick head gasket at about 1.6-1.7 crushed (goals), and maybe a new set of rods for some piece of mind. The rods will be a sure thing if the piston tilt is still seen and I have measured the pistons to find them true to square.

Are their any gaskets available that are thicker than 2.00-.75mm=1.25mm crushed?
I have received offers of good but used rods available from members. These will need new bearings on for the small sides and new bolts as well. At the cost for used, with new bearings, and the machine shop work required, $225 for a brand new set ready to assemble might be be the best deal, especially with the added piece of mind.

Please keep the advise coming in case you seen anything I might have missed.
 
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