Main cap register height

[Pablo]

Are the main cap registers in the block at equal heights (or depth depending on how you want to look at it)?

I am talking about the flat surface in the block that is 90 degrees to the stud/bolt axis for the main caps.

The reason I am asking is to know whether or not I should expect the caps to be the same heights relative to each other if all of the caps were machined to the same height (from their bottom face) for a girdle, , or within a given tolerance (if you could provide one).

Thanks,
Pablo

 

[fastblackracing]

I am assuming that you are replacing the 4 factory cast iron caps with 4 steel main caps? I would not expect the block mating surfaces to be dead even on height as you never know if the the block was mounted true when the factory machine work was done.......I have seen a factory block that the deck height was off .014"!....The cap height and girdle height need to be treated as an assembly.....And you may vary well find that the oil pan rails height will have to cut down some so that you can get to the preload clearance of .004-.005 seems to be what I remember......there is a lot that can get screwed up here and the machinist you choose should be very experienced in doing turbo-buick engines...as they need treated differently on clearances than the typical sbc/bbc engines......If he is not well versed in T/R buicks I would find one that is.....are you attempting to do this work yourself?.....and do you have the instructions that came with the girdle?.....also did you check out turbodave231 sticky at the top of this forum about main cap installations?

 

[Pablo]

Thanks for the reply.

I am not doing the machining myself, but I do all of my own blueprinting and building. I am not mounting billet caps, I have stock caps and have been carefully measuring the quality of my last align hone which turned out to be very poor to say the least. I'm seeing up to .0005 taper, and huge amounts of out of round (like up to .0015). To check whether or not the machinist honed without the pan rail bolts in, I checked that too, and it was no better.
My girdle has been ground flat and I have discovered a small difference in the heights of the caps that would certainly load the caps differently when bolted down (I can rock the girdle slightly). It also changes the clearance to the pain rails, which then further distorts the main bearing bores once the pan rail nuts are torqued down.
I'm certainly finding that the quality of machinists out there is lacking. I have gone through three and they have each been unable to follow simple instructions. One of them has done several 231s even, although I don't know how many were girdled. I'm beginning to wonder if it is possible to find one capable of a proper line hone on a girdled 3.8 at all. I am pretty sure the ones I have used did not re-adjust the girdle to pan rail clearance after taking material from the parting line to perform the align hone

I actually stumbled upon turbodave231's align hone video on youtube a few days ago, very informative. In his video the SBC being honed allows for individual caps to be loosened as they approach spec while others still need more of a cut. How is this achieved on a girdled 3.8? Seems to me like you wouldn't be able to loosen any caps and only end up with what you get with all of them tightened. Also, when taking material from the parting line, is this usually the same amount from each cap?

The method I am using to space the girdle is to use individual spring steel close tolerance shims (like washers) which is a method used for girdle fitment on other engines. I guess my original question should have not been whether they are all at the same exact height but rather what tolerance should I expect. I suppose one method would be to lay a machinist's straight edge across the cap registers in the block but that is one tool missing from my box.

Any thoughts appreciated,
Pablo

 

[A2000RICH]

Are the main cap registers in the block at equal heights (or depth depending on how you want to look at it)?

I am talking about the flat surface in the block that is 90 degrees to the stud/bolt axis for the main caps.

The reason I am asking is to know whether or not I should expect the caps to be the same heights relative to each other if all of the caps were machined to the same height (from their bottom face) for a girdle, , or within a given tolerance (if you could provide one).

Thanks,
Pablo

the cap mounting plane is a dead straight/flat surface (assuming that the block is not damaged) that every measurement on the block is referenced to i know this for two reasons first it just makes sense as it is the centerline of the crank that all the reciprocating parts are attached to and second i have a set of the original 14 page drawings of the 109 block that references just about every dimension to that major surface what is not consistent is the height of the caps since they are produced separately and attached to the block for final bore machining when i machine a block for a girdle i attach the caps (properly torqued) and machine the entire bottom surface of the caps and pan rail in one setup the final dimension i end up with is least i can remove and still clean up all the surfaces actually its pretty simple if you have the right equipment

 

[Pablo]

the cap mounting plane is a dead straight/flat surface (assuming that the block is not damaged) that every measurement on the block is referenced to i know this for two reasons first it just makes sense as it is the centerline of the crank that all the reciprocating parts are attached to and second i have a set of the original 14 page drawings of the 109 block that references just about every dimension to that major surface what is not consistent is the height of the caps since they are produced separately and attached to the block for final bore machining when i machine a block for a girdle i attach the caps (properly torqued) and machine the entire bottom surface of the caps and pan rail in one setup the final dimension i end up with is least i can remove and still clean up all the surfaces actually its pretty simple if you have the right equipment

Thanks for the info. Make sense.
One question though; How do you machine the top face of the caps while they are torqued down?

 

[czimpel]

Thanks for the info. Make sense.
One question though; How do you machine the top face of the caps while they are torqued down?

X2. Aren't the bolt/studs in the way?

 

[A2000RICH]

i counterbore the caps and fasten them down with specially reworked cap bolts i will send pics after i get back from bowling green

 

[turbodave231]

Installing a girdle and doing a quality job is time consuming. I have done a couple and I prefer NOT to do any more. I started by machining the pan rail dead flat and square to the crank. I did this on a CNC machine center that locates off the main bore.

Next, each main bore needs to be reduced by .002-.003 by machining the cap at the parting line. Standard prep stuff for an align honing job.

Then I made a cap measuring fixture that sits flat on the pan rail and bridges over the main cap. A hole in the fixture allows me to use a depth mike and measure down to the top of the cap. I machine the top of the cap to a height +.003" above the pan rail. So when the girdle is installed, the proper preload is achieved without silly shims.

The entire bottom end is then assembled, torqued to spec and then align honed. I have a specific set of stones and shoes for the honing mandrel. I remove 2 stones and 4 shoes from the mandrel to effectively shorten the mandrel. A standard mandrel is just too long for this block. Many machinist who are accustomed to doing V8's with 5 caps think that the standard mandrel will work on the Buick V6. The #1 and #4 main bores end up getting too big too fast. I didn't invent this procedure for shortening the mandrel, it came from my Sunnen Rep who was very familiar with the "buick" process.