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> 2270 Deck Height and CR, Pistons sitting proud of the deck, how many shims is too many shims?
vjb206
post Feb 26 2024, 03:52 PM
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Hey folks! I have the bottom-end of my 2270 assembled and spinning freely. Thanks to all who helped me get to this point!

(IMG:http://www.914world.com/bbs2/uploads_offsite/media.giphy.com-23760-1708984357.1.gif)

To quickly recap: I bought the 2257 kit from AA Pistons (78mm stroke, 5.158" rods, etc.). And when I threw a P&C on for a test-fit last weekend, I immediately noticed the piston sitting proud of the deck height at TDC (negative deck) by about 2mm.

(IMG:http://www.914world.com/bbs2/uploads_offsite/media.giphy.com-23760-1708984358.2.gif)

Before I overreact, or buy the wrong stuff, I thought I'd ping the community...
  1. Is this normal for a stroker set-up?
  2. Can you stack multiple shims when getting up into the .06 >> .09 range?
  3. (If no-stack) What's the best place to have custom shims cut?
  4. I recall Jake saying using large shims requires lots of advance, anyone have experience here? What am I looking to adjust for upon start-up?

Once I figure out whether or not this is normal (I.E. verifying that I don't have to backtrack), I'll get into the CR questions (just waiting on clear plastic from Amazon so that I can measure my CC volume this weekend) (IMG:style_emoticons/default/biggrin.gif)

Thanks!
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Jack Standz
post Feb 26 2024, 08:23 PM
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1. It's all in the combination, what pin height on the pistons, rod length, cylinder length, etc. You might want to rethink your rod length to get a better rod ratio (rod length to stroke). But, yes you're looking at getting some proper thickness cylinder spacers.

2. Measure multiple times and get one spacer per cylinder that are the correct thickness.

3. The type iv store sells them, Blanchard ground to the thickness you pick from their website.

4. Design your motor for less compression or at least, the appropriate compression ratio. If it's too high, it will put out too much heat and you will also need to retard the ignition to prevent pre-detonation. You want maybe around 8.5 to 9.5 max and somewhat dependent upon the altitude you're running it at. You'll want good quench, a deck height probably of at least .040, so cylinder head shape and volume needs to be measured and designed to meet your goals.
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r_towle
post Feb 26 2024, 08:32 PM
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Did you buy the long liners?
I’m guessing those are taller cylinders from AA??

Rich
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Jack Standz
post Feb 26 2024, 08:38 PM
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Strokers are a lot of fun but also a lot more work to get right. Best wishes for a successful build.

BTW, I'm guessing they're not the longer liners.

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Krieger
post Feb 27 2024, 12:16 AM
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Why don't you call AA and see what they have to say? Wrong pistons/cylinders or missing correct spacers
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VaccaRabite
post Feb 27 2024, 06:54 AM
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You are asking the wrong question.
Stop everything else with this build and start here:

What is your target CR? Don't make or buy anything else until you have decided this!

Once you know your target CR, do the calculations (lots of CR calculators online). You will need to know (really know) your head volume in CC for this. Easy to find, but its a little extra work.

At minimum you will need a .123 inch (3.13mm) spacer to give you a .040inch deck height. You MAY need more then that. You won't know until you have done the full CR calculations to figure out your optimal deck to secure the CR you want. If your block is square and cylinders equal all 4 spacers will be the same. Don't count on it though!
You will still need to straight edge the tops of the cylinders to make sure they are aligned flat to each other so they sit right on the head. And don't forget to measure deck on the wrist pin. Otherwise the piston rocks a little on that axis and you will get inconsistent measurements - that get worse the farther you are from the pin axis.

The good news is that once you know, you just call one of the shops above and get base spacers made for your specifications.

I built my first engine just winging it and learning as I built. I learned a LOT. I then rebuilt the engine a few months later when it failed. The second engine ran for years. It was a very expensive lesson. Start with the math and go from there.

What is your CR target. That's the math you need to do right now before going any further. Hopefully you already did the bearing clearance math and fitting!

Good luck!
Zach
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Montreal914
post Feb 27 2024, 11:30 AM
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Read!
Here, on Shoptalkforums, other places…
This is not an IKEA kit.
Before spending big dollars and time, READ!! (IMG:style_emoticons/default/smile.gif)
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cgnj
post Feb 27 2024, 12:11 PM
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@vjb206

That looks like my motor did. It is currently apart on my welding bench waiting for my case, crank, and bearings to come back from the machinist.

I'll measure them and get back to you.
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MikeK
post Feb 27 2024, 12:16 PM
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You can shim the cylinder base, use a copper gasket from the head to the cylinder, trim the top of this piston (not the full amount), use a shorter rod, or use a combination of those things.

You might want to consider using some rubber bands across the head studs and through the small end of the rod to keep them from slapping the cylinder sealing surface while you spin it.
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vjb206
post Feb 27 2024, 01:02 PM
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@MikeK great idea! Don't want any scoring.

@cgnj just knowing that this is not unique to me is very helpful. If you get to it that measurement that would be great, if not, no worries. Out of curiosity - why is the motor apart? Anything inherent in the combo that I should be aware of?

@Krieger I called AA and this is normal (I.E. they didn't send me the wrong pistons).

@VaccaRabite very useful info - thank you! I'm just not there yet... Need to take more precise measurements before doing maths. I'm looking to get to an 8.5 or 9 CR (still deciding which is best).

The cyl head is listed at 60ccs, but I will measure them with fluid this weekend.

I'll follow-up early next week with:
• Head CC ccs as measured with fluid
• _Actual_ deck height as measured with a dial gauge (as I said, the one in the picture is just a sanity check)
• Shim / head gasket plan as a result of more detail

Appreciate everyone who weighed in!

vb
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Jack Standz
post Feb 27 2024, 01:03 PM
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QUOTE(MikeK @ Feb 28 2024, 01:16 AM) *

You can shim the cylinder base, use a copper gasket from the head to the cylinder, trim the top of this piston (not the full amount), use a shorter rod, or use a combination of those things.

You might want to consider using some rubber bands across the head studs and through the small end of the rod to keep them from slapping the cylinder sealing surface while you spin it.


Sorry, must disagree with some of this.

A copper gasket between the head and cylinder won't fix the problem of negative deck height. You'll break the motor on start up.

A shorter rod isn't a good idea (and what size/where would you get one?) as the rod ratio is already 1.68 and going to a shorter rod would decrease it even more.

Trimming the pistons might work, but would not be the first area to consider to fix the negative deck height problem. Start with correcting the other problems and get the proper shims made.
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Jack Standz
post Feb 27 2024, 01:14 PM
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There's more to the compression calculation and an engine build, but based on your #s, it's looking to be around 9.4. That might be high if you're looking to daily drive it and the car doesn't spend its days at high altitude.

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MikeK
post Feb 27 2024, 03:35 PM
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QUOTE(Jack Standz @ Feb 27 2024, 02:03 PM) *

QUOTE(MikeK @ Feb 28 2024, 01:16 AM) *

You can shim the cylinder base, use a copper gasket from the head to the cylinder, trim the top of this piston (not the full amount), use a shorter rod, or use a combination of those things.

You might want to consider using some rubber bands across the head studs and through the small end of the rod to keep them from slapping the cylinder sealing surface while you spin it.


Sorry, must disagree with some of this.

A copper gasket between the head and cylinder won't fix the problem of negative deck height. You'll break the motor on start up.

Copper gaskets are readily available in .040"-.060" and one could get custom gaskets cut. If the piston is hitting the valve/head, then yes, damage will occur. I've run them on a T4 with zero deck to get the deck to .040".

A shorter rod isn't a good idea (and what size/where would you get one?) as the rod ratio is already 1.68 and going to a shorter rod would decrease it even more.

You'd shave the rod end and re-machine it to the correct size, though I agree with you with respect to the rod ratio.

Trimming the pistons might work, but would not be the first area to consider to fix the negative deck height problem. Start with correcting the other problems and get the proper shims made.

That would depend on how much the pistons need to be cut. If your deck height varies from cylinder to cylinder, even with switching around rods, you can fine tune them with trimming the tops of the pistons. Clearly balance them after.


My point was that there are several ways to get the desired result. It's unfortunate that the T4 cylinders that they are selling with their kit don't have longer cylinders like their thick wall, 92's. It's nice to have the cylinders trimmed for the correct deck height and avoid shims altogether.

I guess a shorter stroke crank would solve multiple issues, but I doubt that would be an viable option.
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cgnj
post Feb 27 2024, 04:31 PM
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@vjb206
I lied somewhere. I said my chamber volume was 54cc. It is 52cc. My base cylinder shim is .140 in. I don't use a head gasket. My rods are 5.325 (vw length). I run big valve 44x38 1.8 heads with 2.0 angle 12mm plugs by Headflow Masters. Adrian was the go to guy in 2002.

Why did I take it apart. I have Dirk Wright disease. I took it out to bench run it and look for a tiny oil leak. I still had good compression and leak down above 96%. I replaced my Shadek oil pump because it was at max undersize. I installed a non stock oil pressure relief valve. The part stuck in the bore & I was running without gauges. I took it apart and found the oil pressure relief valve scored. So I decided to replace all of the bearings and rings and cylinders
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r_towle
post Feb 27 2024, 06:09 PM
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You need to swap the short cylinders with the long ones from AA.
Start with that process.
Then you will have a reasonable place to begin measuring.

While you wait, learn how to CC measure your heads, build that jig, get that done
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densible1
post Feb 27 2024, 06:23 PM
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You'll need to shim bottom of cylinder to achieve correct deck height after CR target is determined. There's a online calculator. probably should stay with CR 91 or lower if for street/ available octane rating. The calculation takes in account of head dome dimension.
mark

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VaccaRabite
post Feb 29 2024, 07:08 AM
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QUOTE(vjb206 @ Feb 27 2024, 02:02 PM) *

@VaccaRabite very useful info - thank you! I'm just not there yet... Need to take more precise measurements before doing maths. I'm looking to get to an 8.5 or 9 CR (still deciding which is best).

The cyl head is listed at 60ccs, but I will measure them with fluid this weekend.

I'll follow-up early next week with:
• Head CC ccs as measured with fluid
• _Actual_ deck height as measured with a dial gauge (as I said, the one in the picture is just a sanity check)
• Shim / head gasket plan as a result of more detail


Thats the right path.

If you measure deck height along the wrist pin, a dial indicator is overkill. It does not hurt, but your calipers are precise enough for that particular job. You WILL want that dial indicator later though when you set pushrod length. The problem for this application is that its too precise. You are going to struggle to get a repeatable measurement in the thousandths of an inch that you would not as reliably get to the hundredth with your calipers.

For CR, I'd personally target 8.6:1 for a street engine. This lets you run on regular gas. More importantly, the AA cylinders are iron and uncoated, and will struggle to shed the heat produced by a 9:1+ CR. BTDT. (IMG:style_emoticons/default/headbang.gif) If you want the higher compression, you are going to want to get your pistons coated and the inside of your heads too. And then do the measurements again, as you will have added thickness to the pistons and reduced the CCs of the heads.

The important thing is to pick a CR and get precise - don't pick a range (8.5-9) pick a number and work to that. The changes from 8.5 to 9 are pretty small in terms of deck height. But it makes a big difference in power output and heat and drivability - especially for longer drives.

Zach
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technicalninja
post Feb 29 2024, 09:39 AM
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QUOTE(VaccaRabite @ Feb 29 2024, 07:08 AM) *

QUOTE(vjb206 @ Feb 27 2024, 02:02 PM) *

@VaccaRabite very useful info - thank you! I'm just not there yet... Need to take more precise measurements before doing maths. I'm looking to get to an 8.5 or 9 CR (still deciding which is best).

The cyl head is listed at 60ccs, but I will measure them with fluid this weekend.

I'll follow-up early next week with:
• Head CC ccs as measured with fluid
• _Actual_ deck height as measured with a dial gauge (as I said, the one in the picture is just a sanity check)
• Shim / head gasket plan as a result of more detail


Thats the right path.

If you measure deck height along the wrist pin, a dial indicator is overkill. It does not hurt, but your calipers are precise enough for that particular job. You WILL want that dial indicator later though when you set pushrod length. The problem for this application is that its too precise. You are going to struggle to get a repeatable measurement in the thousandths of an inch that you would not as reliably get to the hundredth with your calipers.

For CR, I'd personally target 8.6:1 for a street engine. This lets you run on regular gas. More importantly, the AA cylinders are iron and uncoated, and will struggle to shed the heat produced by a 9:1+ CR. BTDT. (IMG:style_emoticons/default/headbang.gif) If you want the higher compression, you are going to want to get your pistons coated and the inside of your heads too. And then do the measurements again, as you will have added thickness to the pistons and reduced the CCs of the heads.

The important thing is to pick a CR and get precise - don't pick a range (8.5-9) pick a number and work to that. The changes from 8.5 to 9 are pretty small in terms of deck height. But it makes a big difference in power output and heat and drivability - especially for longer drives.

Zach


This is good but it doesn't tell the whole story.

Your engine parameters are decided due to expected use and EVERYTHING needs to match.
You've got a 2270 which is where I would want to start.
Pistons are sticking OUT of the cylinders. I want this as well.
It's EASY to shim.

Everyone is advising "come up with a CR and target that which is good advice.

When the engine is functional it is NOT the same compression ratio that you modified for.

Cam selection denotes when the intake valve closes during the compression stroke.
Big cams close the valve LATER than small cams and VASTLY reduce compression ratio.
What you're setting with all of the math is STATIC CR. It is a "make believe" number that doesn't actually produce the same ratio when the rest of the engine is taken into account.
What the engine runs on is DYNAMIC compression and everything plays a part.
Camshaft selection has the biggest effect. Timing of said cam is the second most important step.

Too much intake restriction REDUCES the amount of air that can get into engine.
Too much exhaust restriction REDUCES the amount of exhaust that can exit and can trap excessive heat in the system. This is worse than intake restriction in my book.

Exhaust and intake selection also play a huge part on CR and cam selection.

All of Jake's engines say "must have Billy Badass exhaust". There are really good reasons for this.

Try to run that engine through a normal set of SSI Heat exchangers INSTEAD of a dedicated serious exhaust and you need less compression and less cam.
You will accordingly make less power.

Jake always posted about "balance" and he wasn't talking about stuff the machine shop does. He was talking about having all the parts "matched" for the engines intended use.

I'm prone to build to the outer edge of "streetable" and use the highest-octane fuel that I can easily acquire.

The range of 8.5-9.5 should work OK for a street engine. The higher CR needs a different cam than the lower CR.

What it boils down to is EVERYTHING is important at this level of engine.

You should have had an entire plan before the build.

Another thing that Jake stressed was that he had more money and time in the heads than in the entire short block.

Port flow is stupid important in the above engine. That's the biggest sticking point in my build. A 2270 needs heads that can flow 30-50% more air than a 1.7-2.0l engine.

Good heads get expensive fast...

The current crop of heads are Chinese and can have failures.
Jake says he only uses the bare casting and everything he puts in the heads are "bespoke" parts special to him. This says MUCH!
AA offers the heads BARE for just this reason...
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Geezer914
post Feb 29 2024, 11:26 AM
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Almost 1/4" of shims, isn't that a lot? I would look for longer cylinders.
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Jack Standz
post Feb 29 2024, 11:42 AM
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+1

Yes, agree with post #18 from the ninja above.

An example is the 2615 we are starting to build. Some of the particulars are: coated pistons, DFL on skirts, starting with brand new bare heads with modified & coated exhaust ports & combustionchambers/valves, special/custom valve train components (including cryogenic treatments), "nickies" cylinders, custom dual pattern "big" cam with more exhaust duration, etc, etc. Lots of time invested in researching and developing the plan before starting to acquire the parts and starting to machine parts.

As already mentioned, stroker motors are a lot of fun, but lots more work to get right.
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