I'll talk to the Editor about it......I hear he's a hard sell.

 

He's a bit crusty but I think he likes you

 

Adam - wanted to update you.

I have the old ring in the newly "cleaned" bore, and the end gap is big. I have a brand new feeler gauge, and the one that JUST fits is .584mm. Thats very big, and it actually concerns me until I get some new rings in there and see what thier gap is.

FYI

 

Interesting Brendan. That almost exactly what my end gap measurement was with the new ring in the bore. Definitely post what you get with the new ring, it could be interesting. I'm seriously considering going with a custom diameter Mahle Motorsport piston.

 

That is a good idea. I bet it works. It will be rather expensive, but someone sure gave you a good idea.....

Good luck

 

Does "someone" still have TT rear brake sets available?

I might be adding onto my order for pistons. (Taking measurments tomorrow. Can't wait, finally get to use my brand new dial bore gauge.)

 

Hey Adam -

I wanted to share what I have now that some new rings are on my desk here.

With a Mitutoyo digimatic, I have these measurements of just the new ring/vs old ring. I'll get the gap when I go to the garage.

1.48mm thick old
1.49mm thick new

4.16 in "depth" measuring the ring from front to back (old)
4.18-4.22mm on new.

Looks like a .021 or .533mm feeler guage fits in the gap for the new ring in the honed bore on the 89 block.

HTH.

 

Adam,
how about taking a step back and rethinking the whole deal? You need to measure your bores VERY carefully. I asked you if they were round, you never answered....this is a big deal, otherwise, you will never get a good piston fit...no matter where you go for pistons. The piston is only as good as the dimension you tell them to make it to....you make a mistake, it is your mistake, no matter how good the advice is.

Measrue, Measure, Measure...cut once.

Marc

 

Good advice for sure. Adam's bores are as round as they come .... they've just been bored.

 

Hi Marc,

I thought I had responded to your earlier inquiry in whatever string that conversation was taking place. I haven't taken a dial bore gauge to the cylinders yet, I'm hoping to do so very soon.

My understanding is that if the cylinders are round without any stress acting on the block, then I'm in trouble. Because the block was bored with deck plates I'm assuming they will have the correct barrel shape to match the piston skirts. It's interesting that the tech spec books only give one axis for bore measurement, and not two, a cross measurement would be helpful.

I'm currently thinking about plunking down the bucks for the Mahle Motorsport pistons (ferrostan), if they can be had reasonably. Motorsport in UT is working with me on this this. Either that, or its time to hop on the JE/Nikasil bus.

OT: Did you ever see the twin conrod pistoned, v-twin motor that Yamaha developed in the '80's? It was like a V-4, only the piston pairs were siamesed into one big oval piston which had two conrods connected it to the crank. Also, I just read in an import mag that some outfit is custom making cranks and an aluminum V-8 block and bolting Hyabusa barrels (apparently they are modular) to them. Something like 383hp at 10Krpm, at very nominal weight. Now THAT would be ride.


-Adam

So how does this play out Marc, can you tell me what kind of cross bore differential I should be looking for, or do I post the measurements and get a yay or nay.

 

Adam isn't a barrel-shaped chamber still round?

 

Cylinder can give correct result when measured like specified in manuals even though it is far from round when head is on. Now question is will block be round or not when measured elsewhere in bore when head or deck plate is not on? Is deck plates purpose to keep bores round and non moving when bored? Or is it to make them skewed like head makes them thus making them round when in use? If head makes them skewed compared to their free state then obviously they need to be skewed when bored.

 

Adam,
It took me about 24 bores each bored with different plate torques to replicate the stress of the stock head with new stock head bolts! Your bores should not be round! If they are round, beware, if they are round and the piston to wall is at .0008", they may have to scuff in! Not good and risky. I learned this the hard way!

The out of roundness varies with depth of measurement...the MOST important measurement is at the top 1/3 of the bore where the top ring land seats, and "in spec" is just that. always keep in mind that all 928 engines produced by the factory are "in spec", but some make 309 rwhp and others only 270 rwhp....but both are in spec.

You need tounderstand the two ends of the specification...and they are not in the books, at least none that I have.

I need your block, piston and rings to give you a precise answer.

Mahle motorsport USA is not using Ferrostan, but using Garaflex. Applying ferrostan is not allowed by EPA in the US. It is a black coating onteh side of the piston. Ferrostan can only come from Germany.

 

cometic sells direct - my RMR set cost around $225.00 and took 3 weeks for 104mm bores w/928 layout... mahle sells direct on custom stuff too and can coat w/whatever for "offroad" applications, IIRC... last I was quoted, they were up to $275/slug w/ferrostan, pins, rings(maybe no more ferrostan now?)...

if you go nicom, JE and millinium like lots of room for those forged slugs, I had millinium fit mine for .0035" per JE specs, they like'em even looser for boost/nos, ran $800 for coating/200 for boring/fitting - they did mess up some bolt holes by over soaking the block in acid (greg fixed'em up though - superglue?)...

JE is running about 2 weeks on custom pistons lately, FWIW... I had a custom set done (job # 232566) based on a 968 design (for larger valves), and w/sbc pins for sbc rods (carrillo/.927" pins), cost about $686 plus rings and pins w/single oil hole for pin (special deal), they cc'd at about 31.8cc for static comp of about 11.3:1 static... can give more details/specs if you want... hope this helps... these things do get challenging for sure...

looks like mine should be running pretty soon - valve covers are on, just waiting for manifold to come back from powdercoating(carl, you better be in front of a hot oven and not messing around here!), and headers/exhaust from devek (what a vacation? the holidays are over man, back to the salt mine like the rest of us!!), then slap her in and blow it up on a dyno...yiiihaa!

 

686 for 8 pistons + rings and pins? Nice. I only had a quite for 1k.