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Nicklastl
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Joined: July 23, 2024
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Location: Denmark
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 Posted: Sat May 03, 2025 5:43 am Post subject: Aa barrels too low for heads? |
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Hey
Im currently rebuilding my 1700 type 4 and i have a question.
Im not sure, But Im nervous that my new aa cylinders Wont seal properly in my heads. Seems like the “lip” on the barrels a shorter than the chamber in my heads. To my knowledge I don’t know if the heads have been flattened before. I also have another second hand heads which is roughly the same measurement than my old ones.
I’m I complete wrong in thinking that with out any head gaskets then should the lip on the barrels be higher then the chamber in the heads?
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Glenn 
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raygreenwood
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Location: Oklahoma City
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| Posted: Sat May 03, 2025 9:10 am Post subject: Re: Aa barrels to low for heads? |
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What is the actual deck height of the piston and cylinder when at TDC? Just lo9ming at your picture that looks to be ~0.060" (1.524mm) or larger.
I would not add head gaskets of any kind. First, if you already have a large deck, adding a head gasket is going to make that worse....and it makes a HUGE difference on a 1.7L type r engine.
Even the factory had a technical bulletin getting rid of the head gaskets.
What compression ratio are you looking for?
I have some known to be "un-cut" 1.7L heads I can check the bore depth on. But.....there is a visible ring/step on those cylinders that rises above the top fin that looks to be be bigger than 0.060". That could be easily removed in a lathe. That would give you plenty of room. As it is you are missing what.....0.36mm of room?....that's 0.014". If you had an extra 0.025" you would be fine.
Calculate your compression with your current deck first and let's go from there. Try to avoid bead gaskets. Yes, it's simple but not as good as getting rid of head gaskets and having a correct deck height.
Ray |
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Nicklastl
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Joined: July 23, 2024
Posts: 48
Location: Denmark
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| Posted: Sat May 03, 2025 10:51 am Post subject: Re: Aa barrels to low for heads? |
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| raygreenwood wrote: |
What is the actual deck height of the piston and cylinder when at TDC? Just lo9ming at your picture that looks to be ~0.060" (1.524mm) or larger.
I would not add head gaskets of any kind. First, if you already have a large deck, adding a head gasket is going to make that worse....and it makes a HUGE difference on a 1.7L type r engine.
Even the factory had a technical bulletin getting rid of the head gaskets.
What compression ratio are you looking for?
I have some known to be "un-cut" 1.7L heads I can check the bore depth on. But.....there is a visible ring/step on those cylinders that rises above the top fin that looks to be be bigger than 0.060". That could be easily removed in a lathe. That would give you plenty of room. As it is you are missing what.....0.36mm of room?....that's 0.014". If you had an extra 0.025" you would be fine.
Calculate your compression with your current deck first and let's go from there. Try to avoid bead gaskets. Yes, it's simple but not as good as getting rid of head gaskets and having a correct deck height.
Ray |
Im looking for around 7.9 -8.1
havn't really decided yet. I've installed a scat c25 cam. what ratio would you recommend in a bus?
The piston wasn't completly at TDC in that picture, but i did measure the deck height today.
It was 0.65mm. (0.025") and my chambers are 52CC in my heads.
If my calculations are correct, with a deck height of 1.25mm (0.049" total i should get a 8.1 CR.
Wich means i need a shim of 0.6mm (0.023")
But on one side of the engine the deckheight varied from 0,55mm to 0,65mm. Is this normal for the deckheight to fluctuate a bit? or are my block maybe up for a machinest to flattend it?
But back to my main issue, i could be a good solution to have some removed from the "rings" you are mentioning. If i could have a machinist to cut 0.025" as you said. But i still think it's a bit weird. I don't know if it's an AA issue or my heads has been to the machinist a lot of times haha. But could be interesting to see, how deep your heads are.
Best regards
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raygreenwood
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Location: Oklahoma City
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| Posted: Sat May 03, 2025 11:59 am Post subject: Re: Aa barrels to low for heads? |
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| Nicklastl wrote: |
| raygreenwood wrote: |
What is the actual deck height of the piston and cylinder when at TDC? Just lo9ming at your picture that looks to be ~0.060" (1.524mm) or larger.
I would not add head gaskets of any kind. First, if you already have a large deck, adding a head gasket is going to make that worse....and it makes a HUGE difference on a 1.7L type r engine.
Even the factory had a technical bulletin getting rid of the head gaskets.
What compression ratio are you looking for?
I have some known to be "un-cut" 1.7L heads I can check the bore depth on. But.....there is a visible ring/step on those cylinders that rises above the top fin that looks to be be bigger than 0.060". That could be easily removed in a lathe. That would give you plenty of room. As it is you are missing what.....0.36mm of room?....that's 0.014". If you had an extra 0.025" you would be fine.
Calculate your compression with your current deck first and let's go from there. Try to avoid bead gaskets. Yes, it's simple but not as good as getting rid of head gaskets and having a correct deck height.
Ray |
Im looking for around 7.9 -8.1
havn't really decided yet. I've installed a scat c25 cam. what ratio would you recommend in a bus?
The piston wasn't completly at TDC in that picture, but i did measure the deck height today.
It was 0.65mm. (0.025") and my chambers are 52CC in my heads.
If my calculations are correct, with a deck height of 1.25mm (0.049" total i should get a 8.1 CR.
Wich means i need a shim of 0.6mm (0.023")
But on one side of the engine the deckheight varied from 0,55mm to 0,65mm. Is this normal for the deckheight to fluctuate a bit? or are my block maybe up for a machinest to flattend it?
But back to my main issue, i could be a good solution to have some removed from the "rings" you are mentioning. If i could have a machinist to cut 0.025" as you said. But i still think it's a bit weird. I don't know if it's an AA issue or my heads has been to the machinist a lot of times haha. But could be interesting to see, how deep your heads are.
Best regards |
That level of cylinder to cylinder variation is not uncommon. I would swap the pistons around and see if that variation stays there or changes a little. Then swap the rods around. That will tell you where the difference is.
It could be the pistons, could be that the big end to little end distance on the rods is different (thet is worth measuring) and it could be that the journals on the crank are machined a little bit different...or it could be a little of all three.
One other common thing is that the crank centerline can be off from one side of the case to another by a handful of thousandths.
Its also worth setting up the cylinders held down with spacers and nuts and ut a straight edge across the cylinder tops. It is not uncommon to need to have the case decked where the cylinders sit after high miles...and...that side to side difference can be corrected for at the same time when they machine the cylinder seating area flat.
If all is normal....you are actually in the perfect position to do what Glenn suggested. You need about 0.025" MORE deck....and you need right at 0.025" to create clearance between cylinder fins and heads. A 0.025" copper or solid steel shim would work perfectly. Do NOT use the factory laminated shims.
Ray |
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Nicklastl
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| Posted: Sat May 03, 2025 12:11 pm Post subject: Re: Aa barrels to low for heads? |
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I will try to swap around the pistons for a start to see if that changes anything
Are 0.049 in total deck to little? Since you are saying i could go with a 0.025" more?
Best regards
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Nicklastl
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| Posted: Sat May 03, 2025 12:16 pm Post subject: Re: Aa barrels to low for heads? |
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| raygreenwood wrote: |
If all is normal....you are actually in the perfect position to do what Glenn suggested. You need about 0.025" MORE deck....and you need right at 0.025" to create clearance between cylinder fins and heads. A 0.025" copper or solid steel shim would work perfectly. Do NOT use the factory laminated shims.
Ray |
Sorry i'm i bit confused  Where do you say i should put the 0.025 shim? As a head gasket?
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raygreenwood
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Location: Oklahoma City
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| Posted: Sat May 03, 2025 2:32 pm Post subject: Re: Aa barrels to low for heads? |
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| Nicklastl wrote: |
| raygreenwood wrote: |
If all is normal....you are actually in the perfect position to do what Glenn suggested. You need about 0.025" MORE deck....and you need right at 0.025" to create clearance between cylinder fins and heads. A 0.025" copper or solid steel shim would work perfectly. Do NOT use the factory laminated shims.
Ray |
Sorry i'm i bit confused Where do you say i should put the 0.025 shim? As a head gasket? |
Yes.
From your measurements you need about 0.36mm or 0.014" between the cylinder head and the top fin in your cylinder right? A little more to be safe in case of heat expansion would be better.
So.....you also need ~0.635mm or 0.025" of extra deck height right?
So just add a copper or steel head gasket that is 0.36mm/0.025" between the head and cylinder and that will fix both issues at one time.
Ray |
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oprn
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| Posted: Sat May 03, 2025 3:11 pm Post subject: Re: Aa barrels to low for heads? |
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If it were my engine I would trim the top of the cylinders by the top fins. That would let them drop down further into the heads.
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oprn
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| Posted: Sat May 03, 2025 3:15 pm Post subject: Re: Aa barrels to low for heads? |
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If it were my engine I would start by trimming the top of the cylinders by the top fins. That would let them drop down further into the heads.
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raygreenwood
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| Posted: Sat May 03, 2025 9:46 pm Post subject: Re: Aa barrels to low for heads? |
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| oprn wrote: |
| If it were my engine I would trim the top of the cylinders by the top fins. That would let them drop down further into the heads. |
Yep...Kind of what I was getting at early on. That is the most correct way n my opinion.
That being said....his head has been fly-cut. That is the problem.
In reality I got two distinct and consistent measurements on this head
6.39mm and 6.49mm. Its just exactly how I was measuring with my crappy caliper in the dark of my storage unit. The truth is right in the middle at ~6.45mm.
Ray |
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stevet4
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| Posted: Sat May 03, 2025 10:12 pm Post subject: Re: Aa barrels to low for heads? |
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I just remove the 'edge 'on the head with a coarse file, it gave me the clearance i needed.. |
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Alstrup
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| Posted: Sun May 04, 2025 6:49 am Post subject: Re: Aa barrels to low for heads? |
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Shim the cylin ders so you have 1 to 1,1 mm deck height.
Those heads need to be resurfaced. When it is in the machine, ask the operator to skim the fins in the diameter needed.
Standard procedure.
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Nicklastl
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| Posted: Sun May 04, 2025 8:27 am Post subject: Re: Aa barrels to low for heads? |
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| Alstrup wrote: |
Shim the cylin ders so you have 1 to 1,1 mm deck height.
Those heads need to be resurfaced. When it is in the machine, ask the operator to skim the fins in the diameter needed.
Standard procedure. |
Skim the fins of the heads?
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Nicklastl
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| Posted: Sun May 04, 2025 8:31 am Post subject: Re: Aa barrels to low for heads? |
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| raygreenwood wrote: |
| oprn wrote: |
| If it were my engine I would trim the top of the cylinders by the top fins. That would let them drop down further into the heads. |
Yep...Kind of what I was getting at early on. That is the most correct way n my opinion.
That being said....his head has been fly-cut. That is the problem.
In reality I got two distinct and consistent measurements on this head
6.39mm and 6.49mm. Its just exactly how I was measuring with my crappy caliper in the dark of my storage unit. The truth is right in the middle at ~6.45mm.
Ray |
Thanks for measuring! Seems like my heads have been flycut
Seems like there is a couple of Ways around my problem. I Think i’ll talk to a machinist and Maybe Cut the cylinder fins so i dont need a headgasket
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raygreenwood
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| Posted: Sun May 04, 2025 11:19 am Post subject: Re: Aa barrels to low for heads? |
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As you can tell, there are several ways to fix this. All of them work....a few are more "correct" than others.
1. Yes, you could just file off some of the boss on the head and that WILL work but it alo does not fix the issue for later use.
2. Another more correct way is as Alstrup noted. Since you need to have the head sealing areas resurfaced anyway, while its in the mill they can just as easily skim 0.025" to 0.030" on the head fin and boss.
3. Your cylinder itself is not far off but it does have a little excess step you could also skim off in a lathe.
Here are a couple of pictures and measurments. This is a VW branded cylinder and its original piston. This came out of my 1973 VW 412 many years ago. The piston is Mahle so betting the cylinder is too. It is one of my most important piston and cylinders. First, just looking at the carnage reminds/teaches a few lessons.
Second it is a most important cylinder because I keep it around as my 1.7L "mule" cylinder for several items like these measurements I have just taken and also I use it for set up and practice for when I have to do a quick re-profile of a lightly used cylinder set with a flexhone. It helps me to set my stroke rate with my metronome app to get the correct cross hatch angle.
As you can see with just my crappy caliper I got measurements of 6.60mm and 6.70mm as compared to your 6.84mm. That is only 0.005" between my largest measurement and your measurement. Thats a plenty fine tolerance from brand to brand.
Ray |
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SGKent
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| Posted: Sun May 04, 2025 10:40 pm Post subject: Re: Aa barrels to low for heads? |
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what were the measurements? It looked like the cylinder was 684 and the head 710 deep but I can't tell with that digit out. If that is the situation, then the lip/protrusion on the fin has to be milled off. As long as that shortens the head below 684 you should be Ok.
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Nicklastl
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| Posted: Mon May 05, 2025 1:24 am Post subject: Re: Aa barrels to low for heads? |
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Thanks guys!
As i see it, i Can go Two ways.
Either take some materiel of the fin on the cylinders or take some of the head. But if the ‘lip’ on the head is to short to get the correct depth on the head, do you guys say it would be okay to flycut some of the entire surcafe of the heads or am i misunderstanding something?
Might Maybe just be easiest to do all the work on the heads instead of the machinist do both heads and cylinders.
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SGKent
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| Posted: Mon May 05, 2025 10:38 am Post subject: Re: Aa barrels to low for heads? |
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how tall is this lip? Will they fit if it is removed? I you take the top fin of a cylinder off it will reduce cooling. Or shop for new heads.
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Nicklastl
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| Posted: Wed May 07, 2025 1:15 am Post subject: Re: Aa barrels to low for heads? |
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The cylinders and heads have been dropped of at the machinist Yesterday. Luckely he is and elderly man, and have Tried same operations some
Times before. 
Thanks for helping guys
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