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Chrenan · Joined: 15 Jan 2003 Posts: 3903 Location: Canada

Hello all,

It's time to get my spare block in shape. It is completely stripped right now. My question is, what next? I plan on taking it to a machine shop to have it hot tanked and have the freeze plugs replaced - then I'll paint the block grey. Is there anything else I should have them do? I can't get the cyliders bored out because I have standard size high compression pistons ready to go in. Should the cylider walls be honed or hatched in prep for the new pistons? Will this remove any material and mess up the fit of the pistons? Any tips would be greatly appreciated.

Thanks,

Chrenan
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1987 951 - M193 Version for Japan

Diesel · Joined: 03 Nov 2002 Posts: 1061 Location: Ellington,CT

If the block needs to be bored, that's it. Just because you already own standard pistons doesn't mean the block has to accept them. Have the machine shop measure the bores and tell you if a standard piston will work. If it will, have them use a ball hone to crosshatch the bores. I hope you have a good machine shop, there are butchers in that profession too.

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Dan Flanagan--2002 VW Jetta TDI, 83 Mercedes 300D,83 Mercedes Euro-240D

Chrenan · Joined: 15 Jan 2003 Posts: 3903 Location: Canada

If 86.5 mm pistons came out, and the block is from the 86.5 mm casting group, shouldn't 86.5 mm pistons go back in? This level of engine work is newer to me, so I'll have lots of stupid questions. Is it due to wear over time that standard pistons may not work? Distortion and wear of the cylinders over time (20+ years)?
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1987 951 - M193 Version for Japan

numbbers · Posted: Thu Mar 31, 2005 10:26 am Post subject:

Take your pistons with you to the machine shop. They will tell you if they will work in the bores, after the bores are cleaned up.
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1980 924 Turbo

Smoothie · Posted: Thu Mar 31, 2005 11:09 am Post subject:

You or they or someone should look at the cylinder wall wear. Chapter 1 of the Haynes around pages 48-49 shows where to measure - what you'd be looking for is cylinder out of round (they tend to wear into an oval shape as viewed from the top and Haynes fig. 1.15 shows where to measure. "A" and "B" have to be compared to each other at each of the measuring points 1, 2 and 3 to determine the out-of-round wear.) They also wear into a cone shape as viewed from the side, so A1, A2 and A3 get compared to each other and B1, B2 and B3 get compared to each other. Then as they say, if the largest difference between measurements is less than 0.08mm, you can use the same size pistons. If larger than 0.08mm, you should have it rebored to the next larger size.
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"..it's made in Germany. You know the Germans always make good stuff."

'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

My924gtc · Joined: 14 Aug 2004 Posts: 1362 Location: 248

Cool Chrenan and I are going through a rebuild together.

I just got my block back from the shop after having it cooked clean.

If you take the time to remove/replace your own freeze plugs you can save a few bucks. Cost me $55 to have the block cleaned (normally $70 with freeze plugs)

Anyone know where to get the smaller 15mm freeze plugs?

I am using the same pistons that came out of the block so I am not going to worry about fitment.
_________________
MJ
'81 924 2.0L T
'82 924 2.3L SC/EFI <---online fall '06

Sponsor of the 944 Cup and Super Cup
Sponsor of the "2006 Battle in the Badlands"

Chrenan · Joined: 15 Jan 2003 Posts: 3903 Location: Canada

Nice looking block!

Thanks for all the tips guys!
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1987 951 - M193 Version for Japan

Diesel · Joined: 03 Nov 2002 Posts: 1061 Location: Ellington,CT

My924gtc · Joined: 14 Aug 2004 Posts: 1362 Location: 248

Smoothie · Posted: Fri Apr 01, 2005 5:01 am Post subject:

A little more detail on why it makes sense to have the cylinders measured and rebored if necessary...
(Not to belabor the point to you Mark. Of course we're all free to do things our own way - I just want to mention for the benefit of anyone that's interested - )
As cylinders wear (speaking more of the out-of-round wear), the rings are wearing at the same time and they wear into the same oval shape. -So you have odd shaped cylinders with odd shaped rings, but they more-or-less match. Compression may be fair to reasonably good, but not great and the same for blowby and vacuum - they could be better. So an engine overhaul is decided on... Say your cylinders are in fact worn out of spec - if you only hone a crosshatch pattern and put new rings in, you can actually be in a worse position than if you didn't do the overhaul at all since obviously the rings are round and the cylinders are a bit oval. Eventually, the rings should wear into the same shape as the cylinders again, but you're back to where you started and will have gotten a lot fewer miles out of the overhaul than if you'd done a complete rebuild, if it were called for in the first place.
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"..it's made in Germany. You know the Germans always make good stuff."

'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

Joes924Racer · Posted: Sat Apr 02, 2005 5:04 am Post subject:

If its goin to the shop have them check the bores & do a hone
job. I cleaned my block up and replaced all freeze plugs myslef the first time...even did my own hone job after being told that was all
it needed. That was a couple years ago & about 50000 miles ago
next time Ill get a pro hone job. I think its pretty important &
the main purpose of a machine shop. Mark knows what hes doin
Im definatly not sayin he doesnt as thats what I did also.
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1979 porsche 924 Na
1980 porsche Turbo 931GT Replica
Have u ever driven a turbo.

My924gtc · Joined: 14 Aug 2004 Posts: 1362 Location: 248

My924gtc · Joined: 14 Aug 2004 Posts: 1362 Location: 248

If you haven't already, be sure to remove your breather outlet and soak it in de-greaser. Some recommend just backflushing it but after seeing what the screen looked like I recommend removing it and cleaning it really well. It was caked solid on mine.

Also, if when you go to paint it, and if you are like me and you do not want the freeze plugs the same color as the block, I recommend cutting pieces of cardboard using a freeze plug as a template, and wrapping them in the painters tape you are going to use to mask off the block and inserting the into the holes. I just taped off the whole thing and used an architects knife to trim it up.

_________________
MJ
'81 924 2.0L T
'82 924 2.3L SC/EFI <---online fall '06

Sponsor of the 944 Cup and Super Cup
Sponsor of the "2006 Battle in the Badlands"

Joes924Racer · Posted: Sun Apr 03, 2005 3:58 pm Post subject:

The breather outlet 'Mark' how is that removed ?
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1979 porsche 924 Na
1980 porsche Turbo 931GT Replica
Have u ever driven a turbo.

My924gtc · Joined: 14 Aug 2004 Posts: 1362 Location: 248