Sonic testing for wall thickness

[BruceM31]

After what i found i would definetly say yes that is accurate to say.  The tops had alot more meat than anywhere else in the bore.  Cause you gotta figure after combustion happens and the piston drops that 3/4 of an inch pressure in the bore is dropped dramatically making less stress the rest of the way down.

[subsonic]

I was looking at the cyl specs for overbore. Basic is 76.51mm (3.0122in), 3rd overbore is 77.51mm (3.0516in). Difference of 1mm or .0394in.  That would , in stock form-3rd overbore- bring the thinnest  part down to .1206. thats still pretty thin.  How far down into the bore did you start to discover the thinner areas? Can anyone figure out the actual compression area of the cyl? The stroke is 86.4mm. That is taken from TDC to BTC I think.  You also have to take into account piston projection, like when you are measuring for the HG.
So, how far down do we need to worry about?  Do we need to be concerned with wall thickness below the area of the rings? If so, how far below the rings?  Would flex be a problem with thin walls if it ( the thin spot) was below the rings and the aerea where the compression was happening? Whats the general consensus on this?
BY the way.  I tracked down the part number for the 1.7pistons through KS and wrote to them.  

Sir,
I am attempting to locate some information about one of your products, Kolbinschmidt pistons.  In your catalog it is listed under VW, number 32 , part number 079 106, it has a diameter of 79.5mm. It is listed for the engine code KY.  This should be a 1.7D piston.
Does this piston have the cutout for oil coolers (oil squirters)? Is the top of the piston thermally coated?  I plan on using this piston in a turbo charged 1.7 vw block.  Is this an advisable use of this piston?If not could you suggest a different piston.  I am boring out  vw 1.6TD block to accept a 1.7 piston.  The piston pin needs to remain the same-24mm.
Thank you for your time.
Jim Shortill  

 

Dear Mr. Shortill,

yes, this piston has a cutout for a oil nozzle. It is shown on the
picture in the catalogue.

The top of the piston is not hard anodized (thermaly coated)
like the piston for the 1,6 l turbo.

There is no other similar piston which would fit for your purposes.

So if you want to try this experiment with a larger (79,51) cyl - bore and a
piston with a 24,0 pin I am sure it will work if we assume there is a not  too
high boost pressure.

Good success for your work and
a lot of fun on the road.

Best regards
Karl Leitgeb
Senior Product Manager Piston
MSI Motor Service International GmbH
Untere Neckarstraße
D-74172 Neckarsulm
Phone:        +49 (7132) 33 2692
Fax:        +49 (7132) 33 2138
[email protected]

I am still waiting on a response from Mahle Pistons
SO....... let's hope this is all not in vain.  What do you all think about the above questions.
Jim

[BruceM31]

I found it getting thinner about 3/4 of an inch down.  And it wasn't just a gradual change it was fast like there was a ridge or drop off. I would be very concerned about how this the wall will be if you bore it to 79.5mm  cause your wall between the cylinders is going to be paper thin.  You might have flex or worse if you get it to hot from boost blow a whole in it!
Now don't qoute me on that but i'd be worried about doing it after what i saw.

[jtanguay]

wonder if it would be possible to 'build up' material on the block to stiffen it up a bit?

[saurkraut]

Its inside the water jacket.

Is it wet sleeve time?

[BruceM31]

i imagine you could fit wet sleeves  I don;t know how difficult it would be or what is available for sleeves.  I have a block in the machine shop here at work right now that i just had freshly bored for my new motor.  On monday when the machinist are in I can ask them if they think it could be done.

[935racer]

We've done sleeves for these before, although at  current only for .040" oversize for the 1.6 pistons. Would love to do the 1.7 pistons.

[fatmobile]

The gasser blocks are bored out to 83mm stock and I never hear of them blowing holes out the cylinder walls... no matter how much they mod them.
 I've looked at that small space between the cylinders too. It looks thin but the gassers don't have a problem with it.

[fatmobile]

I have my ARP rod bolts now so I can get the rod bushings reemed and get them balanced.
 Nothing stopping me from taking the block in for a clean and bore.
I should have it built in the next few months.
 I still need main bearings with the 3-part third bearing.
 I'm tossed between using the hydrolic block or solid lifter. The solid lifter is bored to the max,... it needs the 1.7 pistons to bring it a new life.
  I haven't opened up the hydroblock to see if it can take another bore.... or what the head looks like.

[webstermike1]

Ive' read your topics and am my self interested in boring out a 1.6 na to a 1.7 or better td. I'm not sure the concern for the cylinder thickness is a real concern, I've been around diesels since 1973, the 6-71 is a two stroke 6 cyl normaly with a blower, and also avail with a blower and turbo, for 325 - 375 hp. half way down the liner there are a series of scavenger holes that go always around the liner. this is where the intake air is passed into the cyl, a set of 4 valves in the head expel the burnt gases out the exaust. I can't remember the stroke but these engines took a load of abuse and kept running and I only saw a very few liners cracked at the scavage holes.

[webstermike1]

:?: After thinking about this a little bit. I have questions. Why are we trying to overbore the 1.6?

In gas engines we increase the cylinder size by overboreing. Since a gas engine is limited to about 12 to 1 compression and a 20% fuel to air ratio the gas engine has it's limits, overboreing is the only way to change the size of the engine. Sure from the 262 Chevy v8 small blocks to the 427 Chevy v8 small blocks the hp is impressive.


In a diesel we overbore to fix an imperfection in the cylinder wall. The size of a diesel is changed by a turbo in present day engines. In Big trucks, they have base engines, 7, 11, 13, and 15 liters. These start about 250 hp and run up to 600 hp. In each series there is hp changes that are controlled by the turbo charger. A 15 liter Cat starts out around 425 hp and runs up to 600 hp by changing the turbo boost pressure. A 600 hp motor uses at full power 80+ psi boost. The rpm of the motor is regulated by the governor 1800 – 2300 rpm. To increase the hp of a diesel with a turbo, you need to know a couple of things, what is the air to fuel ratio, I think its about 15% fuel to air. So how much air can you get into the cylinder? In the VW diesel I think it started with about 58 hp and after the turbo charger it went to 68 hp. When the TDI was released it had a 1.9 liter with 90 hp. I don’t think increasing the 1.6 to a 1.7 would merit all the money invested if the cylinder walls were in good shape. Maybe to the 3rd overbore or possibly to the 5th overbore (http://www.volkswaparts.com/16Pistons5mm.htm ) if you absolutely had to but to invest in sleeves and all the time. I don’t know.  Gale Banks has the fastest diesel trucks and engines available, I plan on emailing him with my dilemma, and running my thoughts past him if he has time to return email. The other source I’ve looked at was Garrett turbo’s (http://www.turbobygarrett.com/turbobygarrett/tech_center/tech_center.html).

After reading everything I believe that the turbo is my answer, but before I can make a decision, I have to find out just how much fuel the injectors and fuel pump can put out. Since we do know that we have to maintain the 15% fuel to air, we don’t know how much air we can add if we don’t know how much fuel can be injected.

[fatmobile]

I got my pistons because the block was bored as big as it could get.
 The engine is in the shop getting bored,
 rods sized because of the ARP rob bolts and bushings bored.
 Anyone sonic test the walls on a 1.8  gasser? Since they can get bored 3mm bigger.