Fred,

It's a bit of a joint venture. Our shop does not have the means to coat, so we use US Chrome. We send them a prepped block* and our torque plate and they plate to our bore spec at our torque spec. It then comes back and we do the final honing if I'm not happy with the bores.

* I'm after perfection, so we hone until all bores are the same diameter and form a perfect cylinder before we send them the block. If you send them what you have you will end up with potentially uneven plating and non-cylindrical bores when the motor is bolted together. That however, will be much better than what you have at the moment.

You will need to remove all the studs which can be problematic. In our case, two head studs broke during removal, so I had to install all new.

Many will tell you that you don't need to bother with all of this and I agree if you just want to get out there and have some fun.

Give me a call if you have any other questions.

Oversized pistons are not allowed. Consider the $400 to do bore work and then the $$$ in pistons you can buy a complete spare car with rebuildable motor for that.


Karl,
I am not familar with any process to restore the bores other than the factory approved Sunnen hone process. Any rebuild motor needs to have stock diameter pistons (tolerance group 0,1,2) and stock bore diameters. They also must use the stock material on the clyinder walls. This is the base material of the block which is call Alusil. The stock bores have no coataings at all.

Hi,

Having been though this problem just in the last few
weeks, I found that the most effective solution was
to go out and find a new block. I pick-up a good
84 block (thanks Nick), matched pistons, and good
valves for around $450. My race shop (csmotorsports)
owner suggest strongly(as in unless you have $1000
to waste) don't bother fixing the block, just find
one in good condition. I know that apartabove and
nick still have a few blocks that would fit the bill.
My engine now is back on target to be done within
the next two weeks.

Sid

What you think of this???






Well it is a trick question.


This is the number 4 cylinder on my 84 block. I ran this motor in my race car from Jan 2003 to October 2008. The gouge in th #4 cylinder was in there from 2003. I made a slight mistake in build it and damaged the wall. At the time the choice was to get a new block salavge as best I could. So a little light sanding and the ridges were gone I and I slapped it back together. I ran the motor like this for 80+ races and it worked great. The reason I pulled it was due to low power. However that was due to leak down on Cyl 2&3 which I traced to leaking valves due to carbon build up. So how BAD are those scratches?


For refererence here are #2 & #3 (2 forward)


and Number 1


All picutres were taken with head off and no cleaning or anything. This motor will be fully torndown, cleaned and built up with fresh seals and bearings. Not sure if I will re-ring or not yet.

Fred,
comparing these two.

yours


Mine


You have more area of scratches, but my gouge seems alot deeper. I think a very light sand by and with fine grit paper would smooth out and high spots and still leave a nice bore. It is really hard to tell how deep those lines are in the photo. I would still pull the piston rings as they may be cracked and that caused this. Also look at the piston to see it it has scuff marks on it. If so the rod could be bent a bit. You will want new bearings on this both main and rod just to be sure.

joepaluch wrote:


Hi Joe,

We have all of the Sunnen stones and paste to hone the Alusil blocks. This was my first step with our 84 block. The scratches came out right away but the bores were still way out of round from wear.

So, now I'm stuck. Do I just put the motor back together with some new rings, or do I get the block as it was when it left Germany? I’ve seen enough of the same problem on the roughly 100 Spec Miata blocks that we’ve done to know that I might have to buy many 944 motors to find the one with good bores. Instead I called around to see how others were dealing with this issue. Here are the options for damaged bores:

-Install metal sleeves and retain the original pistons
-Hone out to the next size piston and buy aftermarket pistons since they are not nearly as expensive as the Mahles
-Nikasil (or NiCom) the bad bores to add material so that the final bores will be exactly as new and reuse the original pistons
-Find a good used block

Note that there is no Alusil plating process. Alusil is just the name for the material used to cast the block.

I chose the NiCom option because it should give me the perfection I seek along with better durability. Perhaps more money up front, but if the bottom end will hold up for years, I’ll come out ahead. It’s not my preferred solution, but I’m confident that I’m tech shed legal. If that does not sit well with some of you.....


Can we spec a custom piston in a non spec diameter, say 0.008 over? This would be by far the least expensive solution that will ultimately get everyone on the same page. These can be built for the class, would come with rings and can be sold through a location that can track them for the class. Can we continue with the current engine rules, but allow an inexpensive solution for the perfectionists out there?

I just can't stand behind the "find another block" solution. Too much uncertainty in too critical an area.