Deck Height - One Cylinder is different, is this okay? Plus 7.3 compression ratio?

[cunning plan]

So I have measured deck height and I have values of:

Cylinder 1: Deck Height: 1.86mm - Compression Ratio: 7.7:1
Cylinder 2: Deck Height: 1.85mm - Compression Ratio: 7.7:1
Cylinder 3: Deck Height: 1.85mm - Compression Ratio: 7.7:1
Cylinder 4: Deck Height: 2.01mm - Compression Ratio: 7.6:1

So Cylinder 4 seems to be the odd one with 2.01mm and a 7.6:1 compression ratio.

Two questions.

Firstly, I want this engine to be a little lazy and not over-stressed as I want to try and make it as reliable as possible. So I was thinking of running below 7.5:1 compression, perhaps 7:2/7:3.

Is this too low, should I aim for 7.5 or leave it at 7.7, or is 7.7 too high?

Second question, is the difference in Cylinder 4 a big problem? I presume you would want them all to be as close as possible? I am using an old case with an unknown history to build this engine and a new AA 1641 kit.

If it is a problem, is it just a case of adding deck height using shims to the other three cylinders to match cylinder 4 - which seems sensible if I want to lower the compression ratio anyway, I certainly do not want to go higher, so hopefully no machining is involved to cut the case on cylinder 4 to match the other 3?

What do you all think?

:?: :roll: :| :| :|

:sign0009:

Engine Specs:
All stock 1600 parts except:
1641 Barrels and pistons
Twin 40 IDFs
Electronic Ignition

 

[K@rlos]

7.7 is fine. It's an increase but nothing dramatic and will accompany the bigger capacity and twin carbs. When I built the 1200 engine in my girlfriends 59' bug i bumped it up a touch and that ticks like a swiss watch. As for the lower cylinder, have the faces on the case had any machine work?

 

[cunning plan]

As for the lower cylinder, have the faces on the case had any machine work?

I have not had anything done to it, but unfortunately I do not know if it has had any machine work in the past either.

Do you think it is worth adding shims to Cylinders 1, 2 and 3 to bring them closer to 2 deck height, therefore running all cylinders at 7.6:1 ? opcorn:

 

[Hubs]

You could take some off the base of the high cylinder. Glass sheet, wet and dry sand paper and thin oil.
Turn ever 10 swirls, 100 swirls is about 0.1mm. Forearms. What's the height like across the top of the 2 cylinders.
Stainless valves have smaller tops so less volume, increasing the head c.c. by about 1cc.
Expensive route.

 

[atafonso]

So I have measured deck height and I have values of:

Cylinder 1: Deck Height: 1.86mm - Compression Ratio: 7.7:1
Cylinder 2: Deck Height: 1.85mm - Compression Ratio: 7.7:1
Cylinder 3: Deck Height: 1.85mm - Compression Ratio: 7.7:1
Cylinder 4: Deck Height: 2.01mm - Compression Ratio: 7.6:1

So Cylinder 4 seems to be the odd one with 2.01mm and a 7.6:1 compression ratio.

Two questions.

Firstly, I want this engine to be a little lazy and not over-stressed as I want to try and make it as reliable as possible. So I was thinking of running below 7.5:1 compression, perhaps 7:2/7:3.

Is this too low, should I aim for 7.5 or leave it at 7.7, or is 7.7 too high?

Second question, is the difference in Cylinder 4 a big problem? I presume you would want them all to be as close as possible? I am using an old case with an unknown history to build this engine and a new AA 1641 kit.

If it is a problem, is it just a case of adding deck height using shims to the other three cylinders to match cylinder 4 - which seems sensible if I want to lower the compression ratio anyway, I certainly do not want to go higher, so hopefully no machining is involved to cut the case on cylinder 4 to match the other 3?

What do you all think?

:?: :roll: :| :| :|

:sign0009:

Engine Specs:
All stock 1600 parts except:
1641 Barrels and pistons
Twin 40 IDFs
Electronic Ignition

1- It is not going to be lazy if you run 7,3:1. In fact, using a lower compression allows you to run more timing, which makes up or more of the power lost by the slightly lower compression. Read on Gene Berg articles, he used lower compression and had great results. I use it on my 1776's with stock cam and they always make more than 70bhp(corrected crank) on the rolling road. Runs very cool and no detonation at all.

2- The difference can be a problem on the sealing surface between the barrel and head. The head will have to be slightly "twisted" to seat properly on the lower cylinder.
Try measuring all four barrels on cylinder 4 and see if it is actually the barrel. If it stays the same, take one barrel, try all four pistons and check. If still the same, you can be sure the barrels and pistons are fine, problem will be the rods wrongly resized(if they have been reconditioned before), crank ground slightly offset or the case surface has been machined incorrectly/worn due to loose heads.
You can check the case and if you don't see any barrel marks, chances are it has never been machined, so my bet would be the rods all else being ok.
On the AA pistons and barrels i found to have differences never more than 0.05mm, but you never know.

4- More than 7.5:1 will contribute for a slightly hotter running engine; you will already produce more heat with the 1641 pistons; 7.7 should be fine but if you preffer more reliability than to extract every single bhp you can from the engine, 7.3 would be your best bet IMHO.

Abel

 

[K@rlos]

Can never understand why people are scared of compression. My stroker motor has run 10:1 for years, never gets excessively hot, detonates or had adverse effect on engine life. Even my 1200 bug is bumped up touch, never gets hot etc. I assume a stock cam is in this 1641? As long as it’s under 8:1 it will be fine. Anymore more would require bigger cam etc.

 

[cunning plan]

1- It is not going to be lazy if you run 7,3:1. In fact, using a lower compression allows you to run more timing, which makes up or more of the power lost by the slightly lower compression. Read on Gene Berg articles, he used lower compression and had great results. I use it on my 1776's with stock cam and they always make more than 70bhp(corrected crank) on the rolling road. Runs very cool and no detonation at all.

4- More than 7.5:1 will contribute for a slightly hotter running engine; you will already produce more heat with the 1641 pistons; 7.7 should be fine but if you preffer more reliability than to extract every single bhp you can from the engine, 7.3 would be your best bet IMHO.

Thanks for replying Abel

Interesting that it produces more power, is that because the spark can be timed to fire earlier in the cycle, almost creating a 'bounce'?

Although, if you are using 7:3, then I will use it! :lol:

2- The difference can be a problem on the sealing surface between the barrel and head. The head will have to be slightly "twisted" to seat properly on the lower cylinder.

this is something I was worried about.

Try measuring all four barrels on cylinder 4 and see if it is actually the barrel.
If it stays the same, take one barrel, try all four pistons and check.

You can check the case and if you don't see any barrel marks, chances are it has never been machined, so my bet would be the rods all else being ok.
On the AA pistons and barrels i found to have differences never more than 0.05mm, but you never know.

Abel

Brilliant, I will follow this to try and figure out what is the issue. I have also bought a DTI / Dial Indicator to help with identifying the TDC as I was going by feel and by taking a couple of measurements, using the average to try and get it right, but an indicator should take the guess work out and make it more accurate. :?

Taking the barrels apart again does provide an opportunity to weigh the pistons I guess, like I said on the other thread you replied to, I had forgotten to do that.

If still the same, you can be sure the barrels and pistons are fine, problem will be the rods wrongly resized(if they have been reconditioned before), crank ground slightly offset or the case surface has been machined incorrectly/worn due to loose heads.

I did forget to mention in the engine spec above, that I am using the used Crank and Con-Rods from the engine, they are not new apart from new main bearings, so it is possible that the crank is not perfect.

IFFF it is the rods, I really, really do not want to take the case apart again. :sad0049:

At that point, as a solution for this 'lazy engine that is a merge of new and old parts', could I just buy x3 wider shims to bring cylinders 1, 2 and 3 down to 7.3:1, along with a thinner shim to bring cylinder 4 down to the same? In my mind, that should match all 4 cylinders together and it should ensure the barrels are aligned for a good seal to the head, right? oke:

 

[cunning plan]

Can never understand why people are scared of compression. My stroker motor has run 10:1 for years, never gets excessively hot, detonates or had adverse effect on engine life. Even my 1200 bug is bumped up touch, never gets hot etc. I assume a stock cam is in this 1641? As long as it’s under 8:1 it will be fine. Anymore more would require bigger cam etc.

Well, this engine is made from a mix of old and new parts, including a tired old case. I just want it to chug along without being too stressed.

In my logical mind, I am thinking: high compression = stress.

I am sure you are right though and would probably push higher if I was building an all new engine.

Orrr, is it better to run a lower compression at all times so you are ready for that beefy turbo? arty0021: :lol:

opcorn:

You could take some off the base of the high cylinder. Glass sheet, wet and dry sand paper and thin oil.
Turn ever 10 swirls, 100 swirls is about 0.1mm. Forearms. What's the height like across the top of the 2 cylinders.
Stainless valves have smaller tops so less volume, increasing the head c.c. by about 1cc.
Expensive route.

This is a good idea thanks, although I will try to leave any DIY modifications to the barrels as a last resort. :character0036:

 

[K@rlos]

7.7:1 isn’t high, far from it, a correctly rebuilt 1600 is 7.5:1 so like I say that isn’t really much of an increase

 

[atafonso]

Can never understand why people are scared of compression. My stroker motor has run 10:1 for years, never gets excessively hot, detonates or had adverse effect on engine life. Even my 1200 bug is bumped up touch, never gets hot etc. I assume a stock cam is in this 1641? As long as it’s under 8:1 it will be fine. Anymore more would require bigger cam etc.

Some people are not "scared of compression", they are only trying to get the best compromise between longevity, power and cost. I think Gene Berg was the most "scared of compression" person i know of, as he used to suggest 6.6-7:1 to most engines :shock:

The fact you have 10:1 and never run hot, have any problems, etc is great. Congrats in being lucky and having the best of all worlds. Does not happen to everybody i know.

Some people have to understand that not everyone is willing to drag race their Buses and have the highest bhp number to show off their friends. These end up with an un streetable engine that is a nightmare in town, horrible fuel economy and high maintenance short lived money pit.

Most Camper owners want(or shall i say need) more torque to cruise comfortably at modern day car speeds but at the same time having reliability, lowest possible maintenance and not a £10k price tag. For those, my suggestions posted on the thread above apply.

I have built not only stock, but countless high powered stroker/turbo engines too, have a nice 2180cc in my Beetle with true forged pistons, h beam rods, 44x37 heads, t3/t4 turbo, etc that is a monster, but i do not keep telling everyone that they need one of those to drive everyday, that would be ridiculous. On the other hand, my 69 Westfalia has a 1600 single port only blueprinted. I love it`s simplicity. Everything has it`s place.

Let`s not transform this nice friendly forum which is full of nice mature people mostly willing to enjoy their Campervans into The Samba, where you can only be respected if you have the highest bhp number from your race engine.

Just my £0.01

Abel

 

[atafonso]

Quick tip for finding true TDC:

Drill a 6.5-7mm hole on your deck height tool as close to the centerline of the piston pin as possible, then tap it to M8. Using a more or less 50mm long bolt, screw it all the way down and nip it. Rotate the crank until the piston hits the bolt. Look at the crank pulley and write down the degree number. Turn the crank in the opposite direction until it stops again on the bolt. Look at the degree reading. Now divide by 2 and you will have EXACT TDC.

Abel

 

[cunning plan]

Quick tip for finding true TDC:

Drill a 6.5-7mm hole on your deck height tool as close to the centerline of the piston pin as possible, then tap it to M8. Using a more or less 50mm long bolt, screw it all the way down and nip it. Rotate the crank until the piston hits the bolt. Look at the crank pulley and write down the degree number. Turn the crank in the opposite direction until it stops again on the bolt. Look at the degree reading. Now divide by 2 and you will have EXACT TDC.

Abel

I have bought the dial indicator now :lol: It's okay, it was £15 from eBay and I will want to use it again when I build a better engine.

By the way, what are you thoughts on below? oke:

IFFF it is the rods, I really, really do not want to take the case apart again. :sad0049:

At that point, as a solution for this 'lazy engine that is a merge of new and old parts', could I just buy x3 wider shims to bring cylinders 1, 2 and 3 down to 7.3:1, along with a thinner shim to bring cylinder 4 down to the same? In my mind, that should match all 4 cylinders together and it should ensure the barrels are aligned for a good seal to the head, right? oke:

Thank you!

opcorn:

 

[K@rlos]

I haven’t tried to make this a ‘my dick is bigger than yours’ debate, he’s asked for opinions. I respect you thoughts on the matter and I have give opinion based on my experience with aircooled Volkswagens and as an engineer.

I won’t bother in the future if it’s just gonna cause disagreements :roll:

 

[atafonso]

Even with the dial indicator, there is a point where the piston is dweling for a bit while on TDC, so the tip i gave will give you an exact TDC point, whereas with the dial the measurement can be off by +-1 deg.

On the shims questions; after all the exercise swoping barrels and pistons, if you still find the difference, try the straight edge this time on top of barrels n.3 and 4 while rested on the case. Try to determine if the problem is with the case or the rod/crank. If you find the two barrels have a straight edge, or same height, i would just rework the n.4 chamber to match the compression of the other 3 if you want to get it perfect.
Now if the problem is the height of the cylinder, only solution will be to turn it down as there are no 0.15mm shims available.
Having 0.1:1 higher compression in one cylinder would not be a big deal in a stock engine, so you can leave it as is as well.
Abel

 

[cunning plan]

I haven’t tried to make this a ‘my dick is bigger than yours’ debate, he’s asked for opinions. I respect you thoughts on the matter and I have give opinion based on my experience with aircooled Volkswagens and as an engineer.

I won’t bother in the future if it’s just gonna cause disagreements :roll:

Perhaps a slight misunderstanding has happened, but we are all a load of bus geeks talking bus. :shadey:

It is fine, I welcome your comments and experience. arty0047:

Even with the dial indicator, there is a point where the piston is dweling for a bit while on TDC, so the tip i gave will give you an exact TDC point, whereas with the dial the measurement can be off by +-1 deg.

I am not totally clear how this would work. Surely you would need to know exactly the length of the bolt and the depth of the deck height tool in order to get a precise depth into the cylinder to make the piston hit as I presume we are trying to get the piston when it is at a certain point in the cycle, but how do you decide where that 'point' is?

I am sure it works, I just cannot understand why it works. For example the bolt you use might be 51mm, then would you not be out by 1mm in the TDC measurement?

:sign0013:

On the shims questions; after all the exercise swoping barrels and pistons, if you still find the difference, try the straight edge this time on top of barrels n.3 and 4 while rested on the case. Try to determine if the problem is with the case or the rod/crank. If you find the two barrels have a straight edge, or same height, i would just rework the n.4 chamber to match the compression of the other 3 if you want to get it perfect.
Now if the problem is the height of the cylinder, only solution will be to turn it down as there are no 0.15mm shims available.
Having 0.1:1 higher compression in one cylinder would not be a big deal in a stock engine, so you can leave it as is as well.
Abel

Okay thank you Abel, I will start checking and measuring everything again to establish what the issue is.

:sad2:

 

[atafonso]

For true TDC, do not use the dial gauge. The piston can dwell on top for a few crank degrees without moving it much, making it difficult to have an accurate measurement with the dial gauge.
The bolt i said will act as a crank stopper, the size is not critical as long as you can stop the crank roughly 1/4 to 1/2 way down.
Fit the deck height tool with the bolt installed, torque it as you would normally. Rotate the crank clockwise until it stops by the bolt. Look at the degree pulley and write how many degrees. Now turn the crank anticlokwise until it stops by the bolt again. Check the degrees. Now take the two measurements, and divide the difference between the two measurements by 2. That is your TRUE TDC. Remove the bolt, rotate the crank until that degree number and there you have it.

Abel

 

[cunning plan]

Before we start with the deck height stuff, I also weighed the AA pistons and as mentioned they are within a two grams of each-other, from 433g to 435g. So a nice job there from AA.

For true TDC, do not use the dial gauge. The piston can dwell on top for a few crank degrees without moving it much, making it difficult to have an accurate measurement with the dial gauge.

I decided to use the dial gauge as I felt for my experience level that I would get a more accurate TDC level than using the 'measure half-way around technique' as I still do not know why or how that method works.

So, try again, using an old rear spring-plate to create a flat metal surface to connect the dial gauge mount to:

This time the measurements are quite different, but still an issue, this time with two cylinders instead of just one:

Cylinder 1: Deck Height: 1.56mm - Compression Ratio: 7.9:1
Cylinder 2: Deck Height: 1.69mm - Compression Ratio: 7.8:1
Cylinder 3: Deck Height: 1.68mm - Compression Ratio: 7.8:1
Cylinder 4: Deck Height: 1.85mm - Compression Ratio: 7.7:1

So I was not close enough to TDC with the 'by feel' technique I tried first.

Next, I tried Atafonso's suggestions of swapping barrels and pistons over until I found a set that match that cylinder, but it made little difference, up to 0.06mm I think was the largest variation.

So what I have above is the best variation to get the cylinders the closest possible.

There are two issues here:

(1) The first is to get all cylinders as close as possible.

(2) The second is the bring the compression ratio down as I feel that would be best for this old case and crank.

(2) is fairly easy as Machine7 have a good range of shims from 0.25 to 2.25mm, so I should be able to get the compression ratio fairly close to what I am thinking (below 7.5 and above 7 would be alright I think).

(1) So with the barrels and pistons eliminated as the cause of this variation in deck height, as stated by Atafonso, that leaves, probably in this order:
(A) The Case.
(B) The Con-Rods.
(C) The Crank.

Now, B and C mean the case has to be split again and everything taken apart. This cannot happen! :sad0049: I am fairly sure that the case would have to come apart if it needs to be machined anyway, so that means A is also not a viable / pragmatic option to be fixed.

So it seems that I will have to find a solution that fixes the issue rather than the cause.

Can I literally Dremel a little flat section out of the cylinder head in cylinder 1 to increase the CC's which in-turn will decrease the compression ratio closer to 7.7 / 7.8?

I would only need to gain 0.5 to 1cc to drop the CR down to 7.8/7.7:

I was thinking of grinding a very light layer off here, marked in green:

If it works, it will bring 3 cylinders down to 7.8 CR and one with 7.7CR. I think that is OK for a stock engine? I guess it is better to only have one cylinder out by 0.1CR than two, OR two cylinders that match, one higher and one lower..... :| :?:

Then as I said above, I will then use shims to bring all CRs down to hopefully:

+ 1mm Shim
Cylinder 1: Deck Height: 2.56mm - Compression Ratio: 7.2:1 [Includes new 50.5cc CC measurement]
Cylinder 2: Deck Height: 2.69mm - Compression Ratio: 7.2:1 (possibly closer to 7.1:1 due to natural 0.5cc increase in this cylinder, not manually done by me as above).
Cylinder 3: Deck Height: 2.68mm - Compression Ratio: 7.2:1
Cylinder 4: Deck Height: 2.85mm - Compression Ratio: 7.1:1 < Now the only 'problem' cylinder, but not enough to cause an issue?

Although the idea seems logical to me, is this a bad idea? Will there be a huge negative I have not thought of? :satanlook: :sign0009:

As always gents, all comments and advice is greatly appreciated! arty0047:

 

[atafonso]

The main thing you need to establish, is if the n3 and n4 barrels have the same height. Try the straight edge on top of them to measure. If they are equal, there will be no sealing problems on the head.
Making parts as equalized as possible makes an engine better in all aspects, that's what we do when blueprinting them. You could live with one cylinder 0.1 point less compression? Yes, but every little helps, the results are more power, fuel economy and specially longevity.
If the cylinders have the same height, i would adjust chamber of cyl 4 to make an equalized compression ratio. Do not go on the green painted side, but on the wall of the spark plug side. That way, the flame will be more centralized, opposite of reworking the green area making the flame having to travel further.

Abel

Ps: The recommendation i am giving is based on the circunstancies presented by the OP not willing to crack the case open. The real way to fix the problem is checking rod lenght/crank grinding issues and addressing it if the seating surface of the cylinders is found not to be the culprit.

 

[cunning plan]

The main thing you need to establish, is if the n3 and n4 barrels have the same height. Try the straight edge on top of them to measure. If they are equal, there will be no sealing problems on the head.
Making parts as equalized as possible makes an engine better in all aspects, that's what we do when blueprinting them. You could live with one cylinder 0.1 point less compression? Yes, but every little helps, the results are more power, fuel economy and specially longevity.
If the cylinders have the same height, i would adjust chamber of cyl 4 to make an equalized compression ratio. Do not go on the green painted side, but on the wall of the spark plug side. That way, the flame will be more centralized, opposite of reworking the green area making the flame having to travel further.

Abel

Ps: The recommendation i am giving is based on the circunstancies presented by the OP not willing to crack the case open. The real way to fix the problem is checking rod lenght/crank grinding issues and addressing it if the seating surface of the cylinders is found not to be the culprit.

Thanks for taking the time to reply Abel, it seems like I have a plan to continue the build now! arty0021: