Advice please on reducing deck height

[StewRat]

Evening all

Assembling my engine, trying to see if there is any possible chance I can get the car running before VW Action.
So far everything has been going remarkably smoothly, albeit slowly due to the overhead of advance research, step by step checking and review, but learning as I went along was always part of this.
Anyway, I have been stopped in my tracks ...

I have 4mm deck height with no shims or spacers.

Not sure why it is so high.
82mm crank and 94mm Mahle stroker pistons with 5.4" rods.
I guess 5.5" rods instead of the 5.4" would help with that a bit, but all the pointers at the time seemed to be that 5.4" were the way to go.

Anyway, what's the best way to reduce it? even a 5.5" rod would only just bring it to the highest deck I would probably want so not a total solution.

Can I get the barrels machined down?

If so, does it matter which end I get reduced? Isn't this going to stop the barrel sealing at the base of the case/head?

Advice appreciated - thanks.

Stewart

[Zach Gomulka]

Hmmm that is odd. Was the case spot faced properly when bored for 94's?

[StewRat]

The case was previously owned but unused when I bought it. It's a CB case, and was bored, clearanced, full flowed etc before I got it.

Thinking about this more, the barrel seats fully in the case, so removing barrel material there would have no impact on the deck. At the top of the barrel, the collar that inserts into the head is about 1mm longer than the head recess, removing anything more than that would bring the external shoulder of the barrel in contact with the head so wouldnt actually bring the piston any closer to the head.

There is a 2mm pad of material around the combustion chambers. I see pics of heads without that. Removing 1.5mm of it would let the (1mm shortened) barrel get further into the head for a 1.5mm deck height and 10:1 compression ratio.

Is all that a solution or am I approaching this wrong?

Thanks

Stewart

[neil68]

In my 2332 cc, I run a 2.5 mm cylinder shim with a stock magnesium case.  I have run 1.5 mm deck height in my street-strip Beetle and still obtain 200+ HP to the wheels.

The piston support at BDC still seems to be fine, as I've run this for years.  You could probably run a 3.0 mm shim, since you're only using an 82 mm stroke. This would give you 1 mm DH, which seems to be the minimum that most racers recommend.

[richie]

Cb cases come with raised deck, you can either get the deck on case machined down or trim cylinder, you have to trim snout and seating surface equal amount so cylinder goes into case more but snout doesn't get hit by crank or rods

cheers Richie

[StewRat]

Thanks for the input guys.

@Neil - cylinder shims would take me the wrong way wouldn't they? I'm trying to reduce the deck height.

@Ritchie - I hope I'm interpreting your terminology correctly - by snout you mean the thinnest part of the cylinder base that goes into the case?

If so, I dont know if that CB raised deck has already been dealt with on this case, but the cylinder is pretty much fully inserted in the case, up to the shoulder.
So I don't think that reducing the snout, or lowering the seating surface within the case bore would change anything.



It feels like my only chances of reducing DH are at the cylinder head end. What is the function of this pad surrounding the chambers, and can I remove some/all of it?



Assuming for the moment I trimmed (say) 3mm from the top of the cylinder, the piston would be 1mm from the top of the cylinder, but wouldn't seat fully in the head because the shoulder would hit that pad before the snout hits the sealing surface.
Removing 2mm (effectively all) that pad would let the cylinder seat with 1mm DH.

BUT - this is me thinking out loud rather than an action plan right now. I dont know if I would be causing other problems by doing this.

Is it safe to do?

Thanks again!

[richie]

Thanks for the input guys.

@Neil - cylinder shims would take me the wrong way wouldn't they? I'm trying to reduce the deck height.

@Ritchie - I hope I'm interpreting your terminology correctly - by snout you mean the thinnest part of the cylinder base that goes into the case?

If so, I dont know if that CB raised deck has already been dealt with on this case, but the cylinder is pretty much fully inserted in the case, up to the shoulder.
So I don't think that reducing the snout, or lowering the seating surface within the case bore would change anything.



It feels like my only chances of reducing DH are at the cylinder head end. What is the function of this pad surrounding the chambers, and can I remove some/all of it?



Assuming for the moment I trimmed (say) 3mm from the top of the cylinder, the piston would be 1mm from the top of the cylinder, but wouldn't seat fully in the head because the shoulder would hit that pad before the snout hits the sealing surface.
Removing 2mm (effectively all) that pad would let the cylinder seat with 1mm DH.

BUT - this is me thinking out loud rather than an action plan right now. I dont know if I would be causing other problems by doing this.

Is it safe to do?

Thanks again!

If you cut seating surface on case or on cylinder it will lessen deck height by that amount, if you cut case then cylinder moves in further toward crank so piston is affectively higher in cylinder, same if you cut cylinder to case sealing surface, cylinder is shorter so piston is nearer top

And yes you can cut the pad of heads, even cut fins off if needed but really that's wrong end to cut at moment

cheers Richie

[StewRat]

Right - nearly there I think.

Sorry - my mixed terminology and some misunderstanding about sealing surfaces has confused and slowed this down, but I may have got it now.

In this poorly labelled pic:



If A=19mm, and B=16mm (ie the 16mm snout doesnt reach the bottom of the 19mm deep bore in the case) then I could remove <3mm of what I have been calling the "shoulder" but is better described as the cylinder sealing surface and that would get the cylinder 3mm further into the case and reduce DH by 3mm ??

If I also removed 3mm from the (unlabelled) end of the cylinder snout then all the original relationships around insertion depth, gaps etc would be maintained.

Have I "got it"??

Thanks!

Stewart

[richie]

Right - nearly there I think.

Sorry - my mixed terminology and some misunderstanding about sealing surfaces has confused and slowed this down, but I may have got it now.

In this poorly labelled pic:



If A=19mm, and B=16mm (ie the 16mm snout doesnt reach the bottom of the 19mm deep bore in the case) then I could remove <3mm of what I have been calling the "shoulder" but is better described as the cylinder sealing surface and that would get the cylinder 3mm further into the case and reduce DH by 3mm ??   yes but you should cut some off snout really as you need some clearance to that step inside case



If I also removed 3mm from the (unlabelled) end of the cylinder snout then all the original relationships around insertion depth, gaps etc would be maintained.  end that goes to head? if you remove 3 mm off there it will lose 3mm of deckheight but it wont seal against head unless you cut some off head to stop fins touching head before it seals

Have I "got it"??

Thanks!

Stewart

[StewRat]

"end that goes to head? "

No - as advised, talking about doing all this at the bottom of the cylinder, end that goes in case, and for avoidance of doubt, only talking about machining one part - the cylinder. No case or head machining.

" yes but you should cut some off snout really as you need some clearance to that step inside case"

That's what my second sentence means - machining a corresponding amount off the snout to restore all the previous clearances etc.

Really appreciate your help with this - and for sticking with my unhelpful descriptions etc. Every day is a school day on this project.

Thanks

Stewart

[richie]

Cb cases come with raised deck, you can either get the deck on case machined down or trim cylinder, you have to trim snout and seating surface equal amount so cylinder goes into case more but snout doesn't get hit by crank or rods

cheers Richie

See in red    I think we got there in end   , only reason to do case really is if you damage a cylinder you cant just swap them out, you have to machine a new one, if you mod case then cylinders are straight replacement in future

[StewRat]

We did indeed get there.

And the clues were in the earlier notes as you say.

While noting the possible need for later cylinder swaps, this approach has the appeal of only needing the cylinders to go out for machining, and I can leave the assembled case as-is, for the moment at least.

Thanks again.

Stewart

[Chip]

We did indeed get there.

And the clues were in the earlier notes as you say.

While noting the possible need for later cylinder swaps, this approach has the appeal of only needing the cylinders to go out for machining, and I can leave the assembled case as-is, for the moment at least.

Thanks again.

Stewart

Decking the case means that cylinders don't need to go out for machining. I think what you have there is a CB raised deck case. It's made for an 86mm+ crank with a long rod, allowing you to avoid shims. Just trim down the deck on the case in my opinion. Obviously verify that the rods don't smack the bottom of the cylinder, and trim as needed there too, but don't think you'll have a problem.

[StewRat]

Well the next problem is that the place I had expected to do the machining arent VW specialists and are saying they think they will have problems securing the barrels due to shape and fins.
And quoting  £35 -40 + VAT per barrel IF they can be secured.

They'd probably have better luck securing a case half to deck that, but I'd be limited to >1mm DH if I can't get the barrel machined down too. And I'd have to dismantle the case.

Unless I can find someone more confident in machining the barrels (I'm in Fife, Scotland) then that may be the better way.

Stewart

[Chip]

I didn't realize there was a step inside the bore in the case. That's pretty lame. I think the answer her is a longer rod or bigger stroke   

[Zach Gomulka]

I think the answer her is a longer rod or bigger stroke   

Yep, a 90mm would put it at zero. Easy solution!

[StewRat]

I think the answer her is a longer rod or bigger stroke   

Yep, a 90mm would put it at zero. Easy solution!

Indeed. 

However plan A is currently to follow up on a couple of leads for local machine shops to trim the cylinders.
It's a bit short-termist compared to reducing the raised deck on the case, longer rods, etc, but if they can do it and quickly it will keep things moving forward. I'm off work for the next 2 weeks so chance to get stuff done if I get past this roadblock.

Thanks all.



 

[Zach Gomulka]

I think the answer her is a longer rod or bigger stroke   

Yep, a 90mm would put it at zero. Easy solution!

Indeed. 

However plan A is currently to follow up on a couple of leads for local machine shops to trim the cylinders.
It's a bit short-termist compared to reducing the raised deck on the case, longer rods, etc, but if they can do it and quickly it will keep things moving forward. I'm off work for the next 2 weeks so chance to get stuff done if I get past this roadblock.

Thanks all.
 

That's the right way to do it

[StewRat]

Thanks again to the VW community, got a lead from a club member for a local machine shop.
One of the owners there knows VW engines - he has a modified one in his .... helicopter!!
Easy job for them, get them back later today, £5 each. Can't complain at that.

Back on track...

Thanks again for all the guidance here, I've learned loads

Stewart

[richie]

I think the answer her is a longer rod or bigger stroke   

Yep, a 90mm would put it at zero. Easy solution!

Indeed. 

However plan A is currently to follow up on a couple of leads for local machine shops to trim the cylinders.
It's a bit short-termist compared to reducing the raised deck on the case, longer rods, etc, but if they can do it and quickly it will keep things moving forward. I'm off work for the next 2 weeks so chance to get stuff done if I get past this roadblock.

Thanks all.
 

That's the right way to do it

Zach, don't you think cutting case down would be better? at moment he hasn't got much cylinder in case to support piston at BDC and cutting case would improve this were as cutting cylinder not so much

Stew ask them to take as little as possible off spout, just enough so it doesn't hit that ridge inside case

cheers Richie

[nicolas]

for what it is worth. i did machine my case (regular type1) to match B pistons with a 78 crank. there wasn't too much material removed, but the raised edge is gone and i have the seating surface about 1mm below the casting. so it lies deeper like in the pictures allready posted.
i read that your machine shop has difficulties to machine the cylinders, that troubles me a bit. i know it isn't just trowing the thing in the lathe, but with a wide enough center and easy approach this can be done fairly simple in a lathe.

[StewRat]

@Richie. Is that 16mm of cylinder inside the case less than normal? The job was done today and I told them to remove same from spout and from seating surface so the relationship would be the same as before.

@Nicolas. That was only the first place I tried. The place I found later have no concerns with the job at all.

[richie]

@Richie. Is that 16mm of cylinder inside the case less than normal? The job was done today and I told them to remove same from spout and from seating surface so the relationship would be the same as before.

@Nicolas. That was only the first place I tried. The place I found later have no concerns with the job at all.

No length is normal but your cylinder is sitting further out than normal due to raised deck design of case so piston comes further out bottom of cylinder, that case is for bigger strokes really

[Zach Gomulka]

I think the answer her is a longer rod or bigger stroke  

Yep, a 90mm would put it at zero. Easy solution!

Indeed.  

However plan A is currently to follow up on a couple of leads for local machine shops to trim the cylinders.
It's a bit short-termist compared to reducing the raised deck on the case, longer rods, etc, but if they can do it and quickly it will keep things moving forward. I'm off work for the next 2 weeks so chance to get stuff done if I get past this roadblock.

Thanks all.
 

That's the right way to do it

Zach, don't you think cutting case down would be better? at moment he hasn't got much cylinder in case to support piston at BDC and cutting case would improve this were as cutting cylinder not so much

Stew ask them to take as little as possible off spout, just enough so it doesn't hit that ridge inside case

cheers Richie

If the case is just mocked up now then definitely remove material from the case. I do usually prefer modifying the cheaper part though. I don't think 4mm is terribly crucial in this situation. It is really hard to grasp exactly what is going on here though (new to up VW's, terminology, etc). I'd recommend someone with more knowledge put their fingers on it before getting out the cutters.

[DWL_Puavo]

A bit late for this thread, but I would have suggested "cheap and easy" solution: "a" -pistons, eg. "not stroker" pistons, eg. "69mm stroke" pistons as they could have been swapped for your current cylinder set for pretty much free. Downside is that the engine would have been extra wide as you've also have to add about 1 - 1,5mm of barrel shims or cutting the head ridge for the needed ~1mm. With barrel shims there could have been lenght problems with pushrods / valve rocker geometry.

...So supposedly cutting the barrels is the correct way if you didn't want to increase stroke or change the whole case.

[Zach Gomulka]

I don't think A pistons would be much of a solution, they would require extensive clearancing on the skirts to clear the crank at BDC.

[DWL_Puavo]

Are the piston skirts that much taller in A pistons - relatively to the wrist pin? Usually the pistons themselves are shaped differently and in a-pistons those skirts are way more, how to say it, ...prominent But is it still that much a problem with 94mm pistons? I would also imagine that there exists shorter stroke pistons without the "classic" barrel shape, eg. similar pistons to the "b" -pistons but with raised top?

In smaller sizes there is quite a lot of skirt-slimming needed. This said - I've neved tried A-pistons with longer strokes than 74mm and I also haven't had raised deck case. So this is a bit academic on my side.

[StewRat]

Fastest way for me to resolve this and proceed with the rest of the build was to reduce the barrels.
I now have 1mm deck and 10.7 CR - both I think fairly conservative to get things up and running, which is the primary objective - make some passes before the end of this year, *possibly* even at VW Action, then refine over the winter for next year.