Crankshaft Crossroads - Now 2027 Build

[Rob Combs]

[Rob Combs]

All right got a chance to dig back into this.

Picked up some shims from Scat yesterday, came home and measured them - they were a tiny bit thinner than the .020" advertised.

I let my OCD kick in a little, even considering Brian telling me I'd be just fine, I went and picked up a set of Empi shims as well (had to go to LAX, so stopped by an Empi distributor on the way - didn't really have to go out of my way so why not), came back and measured those, and found that they're very close to the same thickness as the Scats, but the max variance from shim to shim was a little higher.

Cutout for studs much better on the Empis, and not properly clocked at 90 degrees apart on the Scats, so I'm going to trim up the ones that are off a little at the actual stud locations with a hole punch and deburr again.

I mocked it up for the third time using the Scat shims.

As I suspected, it turns out I did make a technical error in projecting my deck heights, when I said I was under .001" variance after trading rods around a couple nights ago. With the Scat shims in hand I was able to go an actual measurement - turns out I'm at a max deviation of .00157", measured, not projected.

Deck heights:
1) .0429"
2) .0425"
3) .0413"
4) .0429"

All within the .040 - .045" window and right down the middle. I'll take it! Couldn't be happier with this result!

(This is why it is absolutely necessary to actually mock up and measure! Especially for you guys that have to order parts and wait for delivery and/or have parts machined - you don't have the luxury of just running down the street and getting more parts.)

I was all concerned about deck being too tight based on calculations and here we are where we want to be...


Now the not so good news, but maybe it'll be ok...

I was pushing the piston out of the last cylinder (to get weights), and the combination of my unsteady hands and the friction of the piston with rings combined forces to have me launch the piston out of the cylinder like a rocket, where it - of course - hit the metal edge of my desk. This caused a nick in the edge of the #2 piston:

I cleaned up the outstanding protrusion (to the side and up top) with my least-aggressive file, polished it with some 600 grit wet or dry, then with some 1500 wet or dry wrapped around my mini-files so I could get into the groove that it left behind as well. You can no longer feel the protrusions that were above the piston surfaces; only thing you can still feel is the little groove, but it's smoothed off.

Here it is in the cylinder:

Like I said, hopefully that will be ok. Piston weights, after doing some pin swapping, with circlips but without rings are 456g each. I've seen far worse pistons run for a very long time.

Expecting my CB order today so on to cam degreeing, cam bearing measurements, and lifter rock measurements.

Then onto piston/cylinder clearance and ring gapping. Will have some questions specific to AA cylinders when that time comes. Got a set of Grant rings.


That's all for now; thanks for all the advice and support!

[chrisflstf]

The stud spacing for cylinders is not symmetrical. There is about .150 to .200" difference in L/R vs U/D dimensions. I cant speak for alum cases, but on brazil or mex its not the same. The shims may vary also as to how the cutouts are clocked. Ive seen them differ that way also

[Rob Combs]

Ok thanks for that!

That's probably where this is stemming from. I did not notice the assymmetrical clocking or even think to look closely enough to consider, but makes me feel better about the mfg quality of the shims I have. I just verified my DH and pulled the cylinders back off; went no further today.

My own operator error is easier to correct.

[Rob Combs]

Got my Clevite Bearing Guard from Summit today. I gotta admit it's some nice stuff.

Also got some more done this morning.

Pulled the rods back off the crank and put them back in the box for safe keeping. They'll probably stay put away until I have some heads put together. Will clean them up and put said Bearing Guard on the bearings upon reassembly.
 
Lapped cam bearing thrust surfaces to .002" end play. Checked lifter to cam lobe clearance - can stick a pocket screwdriver in there with plenty of room to clank it around, so no problems there. Lifters are tight in the bore - no measurable side play.

Plastigauged the cam bearing oil clearance and ended up between .0015" and .002", more toward the .002" side of the window - that's where I was with a snap gauge in the #1 and #3 bearings as a sanity check, and can't get to the #2 bearing at all with the case torqued up, so gonna have to leave it at that.

Next up - getting the cam gear on, dropping the crank back in, checking end play on the crank, and measure out the cam timing. Then on to measuring piston to cylinder clearance, and checking ring end gap. Should be able to get to that stuff later this week/into the weekend.

Then it'll be time for a set of heads...

[Rob Combs]

Made a little progress over the weekend and yesterday -

Cam is degreed in, made a flywheel puller so I could get the end play shim set locked down, and now doing a final sanity check on case and cam clearance. Need to remove a bit from the case on the #2 cam bearing tower.

Now for the tricky part - cam to rod clearance came in right at .035", just a whisker below the reccommended .040".

Now I'm betting a 78.4 stroke crank would've cleared with the whole .040". Oh well, still no regrets on the 78.8.

Is this something I need to take over to the machine shop to have about .010" taken off around the entire circumference with a lathe, or can I clearance this by filing it a little flat at the points on the cam body where it's a bit too close?

[Brian_e]

I would just run it. You have good parts, and this thing won't be spinning real fast.

Or you can zip the corners off the rod caps a fuzz more on a belt sander. I usually round them over before I start any build. It doesn't take much to add quite a bit of clearance, and it won't effect the rod strength at all.

Brian
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[Rob Combs]

Thank you for the suggestion Brian!

I may take the "ounce of prevention" mindset and knock just a tiny bit off those rods. They needed to go in for balance before final assembly anyway.

Just a little bit of case (and rod) work left to do, so I disassembled the rotating assembly this morning and mothballed it - going to slow things down a bit while I get the heads figured out. Will work the piston measurements and ring gaps in while I figure out the heads.

[Rob Combs]

Just to keep the lower end of this thing moving forward, I probably need to start thinking about a pressure plate so i can arrange for balancing work.

At what point does a KEP 1700 pounder become necessary? That’s where my mind is going at the moment.

Any better solutions that i may have missed?

I expect this thing to have some pretty substantial torque when it’s all said and done.

[chrisflstf]

KEP Stage 1 and a long arm is sweet. Can push the clutch in with your hand no problemo.

Just make sure the PP is a tight fit in the flywheel and has no slop to move around

[Rob Combs]

Thanks for the input!

I suppose if I really want to go the extra mile I could have the machinist pin the pressure plate to the flywheel prior to balancing so it stays located anytime it's taken apart and reassembled - hopefully not often!

Am I going beyond what a 1200-lb Sachs pressure plate can handle? How about with a fancier disc? (I'm guessing I'm pushing it with the 1200-pounder and a stock disc.) Is Sachs' quality control all over the place?

Just looking to build it strong enough, but not so strong I start breaking other stuff (clutch cross shaft & bushings, cable tube, pedal hook, etc.). Berg's site says there isn't too much more tension on the cable, etc. going with the KEP as long as it's set up properly.

Is that everyone else's experience?

[Rob Combs]

The engine balance thread solved the pressure plate question, so on to the next one.

Sorry if this comes across as a bit wishy-washy, but hear me out on this one, please - Some of you will be beating your head on the wall and others will think I'm finally coming around. I know this was a less-common build concept, running a 2027 with a single PICT carb, but doable, and I like the simplicity. But I know I'm leaving a lot on the table with that concept too.

That said, after looking at the pile of parts I have, the list of parts that I still need, the amount of work that will be needed on those parts, and what options I could exercise, I am considering practical "strategic options". I have to build to damn near a turnkey state before I can even think of installing a new engine, due to my garage limitations and lease terms. I may even have to find another place to do the install once built. So building to what I had planned is going to take a whole lot more parts and many will be duplicates of what I already have, just to get to another turnkey state with the original design in mind.

But...

I do have a complete set of DCNF 40s with extra venturis, jets, accelerator nozzles, Berg linkage, Berg manifolds, vacuum pickup adapters, ready to go with all the trimmings, and they weren't very popular when I had them posted in the classifieds so not going to sell easily for what I'd want for them. But they're complete and they do run well.

I also have a lower end that I planned to turn into a 1776 anyway. And I know if I sell the car, I will not recover my money from the 2027 as part of the sale, but if I can pull together a fairly strong (~ 80 HP) single carb 1776 to sell in the car for very little incremental funding, it might be money well spent if/when I get to that point.

A well-built turnkey 2027 could be sold separately and I'd have half a shot at getting something back out of it if separate from the car.

So, if I were to put the 28.5mm venturi 34PICT-3 in the 1776 build pile, along with the CB center section and other bits I've got, and reimagine my 2027 build with the DCNFs, that would maximize the use of what I already have and minimize what I still need to buy.

Which brings me to the questions - IF I go the route of utilizing the DCNFs, the cylinder head situtation gets a lot more simple to solve (probably CNC Panchitos, preferably single HD springs - dual springs are negotiable), but should I keep the 2239 cam I already have, or move that to over the single-carb 1776 parts pile, and move to a more sporty cam for the 2027 in a full-weight Ghia with late (SSC) stock gears? Powerband would be nice coming in early around 1500 but the sky is the limit on the top end as long as we can be reasonable with valve springs and valvetrain stress.

If a cam change is in order, I already have TP lifters on the shelf. I also have 1.1:1 AND 1.25:1 back-cut rockers with TP swivel adjusters, and I have Berg 1.45:1 rockers on the engine that's currently in the car. Will probably go with another set of Smith Brothers pushrods once lengths are known. So the valvetrain will be fairly light and I have almost wide open options with respect to the cam, constraints being the Panchitos and the DCNFs, and of course cam availability.

If I'm going to change direction this is the time...I'm still working out all the details in the lower end.

So, what would be your cam suggestions for bumping back up to dual carbs, if I may ask?
Web 163? 218?
Is there an Engle ratio rocker cam that will fit the bill? (Engle and Berg are REALLY easy for me to get with SoCal just up the freeway and Berg not too much further. And it would be fairly simple to convert the engine currently in the car back to 1.1:1s to retrieve the Berg rockers for the build.)

Any suggestions are welcome. Thank you in advance.

Rob

[modok]

Good post. I'll think about it when I'm less wasted.

[Rob Combs]

Didn't want to buy a belt sander to clearance the rods, so I took a little bit off of them with the tools I have on hand, as much as I was comfortable removing.

Still a little too close on the rod end to cam clearance for my comfort, and since I was contemplating going a different direction anyway, I ordered a stroke-clearanced CB 2242 this morning.

Back to mock-up sometime next week (I hope). Once I'm comfortable with its clearances, it's off to the balancer for the rotating parts.

Nearly ready for heads now...

Rob

[Rob Combs]

Quick question

Got my 2242 cam in; most clearances look great now. The one clearance I forgot to check before breaking it back down was the cam lobe to counterweight clearance, so I'll take a look at that sometime next week. After lapping the thrust bearings, end play was right at .002" with the 2239, but is ~ .0035 with the 2242.

Bentley spec for stock cam/stock springs is .0016"-.0050", so I'm at the mid-high end of the window for stock stuff. Wear limit in the manual is .0060". I'll be running dual springs per CB's advice.

In this scenario, would you run it as-is? Or should I get another set of cam bearings and tighten it up to .002"?

In other words, how mission-critical is it to be at the low end of the end play spec?

Thanks as always for any advice.

[Alstrup]

Opinions vary. I go for minimum clearance. As soon as the cam spins freely in the case I stop. Thats usually less than- or around 0,05 mm (0,002") I do not see the need for more unless the engine is reved high, like 6500+. Then it needs a hair more.
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[modok]

I think it's fine
The angle on the gears and force of driving the oil pump keeps the cam pushed toward the flywheel when the engine is running. So really only one thrust face matters when the engine is running, the one on the side of the cam gear.

But if the cam thrust play is excessive when turning over the engine by hand you may hear a "sproing" at one or two spots in the rotation from the cam thrust reversing. This may be confusing, wondering what that sound is, but it doesn't hurt anything.

Old time German engineers did not like any strange noises, and tight was good, so they made sure to keep everything tight even if it doesn't really matter.
Meanwhile, in the rest of the world, the rattle of a super cub, or a ducati clutch, or a how a harley lopes, end up being considered a special quality, but you do have to be aware of it, otherwise you might think there is something wrong it.
And chevy built the most popular v8 in the world with nothing holding the cam in, nothing stops the cam from falling out of the front of the engine at all besides the cam taper, and yet it works. well, as long as you don't try to use a roller cam in it anyway, then you need something to keep the cam from walking out.

[Rob Combs]

Thanks for the input fellas!

I hope my machinist can take in the lower end parts for balancing today, so while I'm there I will see what he has in stock in terms of cam bearings. There seems to be a bit of a shortage on Mahle cam bearings at the moment, at least with the double-thrust variety.

I'd actually prefer a little tighter even if it will probably be just fine as-is, because in my mind the tighter end play doubles the wear capability before the service limit is hit. Probably all academic anyway because I will probably never be able to put the kind of miles on this thing that wears out thrust bearings, and would probably have to open it up for something else beforehand, if I ever even get to that point.

So I'll probably just let the market decide. If they have the Mahle double-thrusts, or even if they have the Silverlines at a decent price, I'll replace them and use the fitted bearings with the 2239 cam they were matched to on a later build.

If not, maybe just proceed with what I have. It's not like it's going to immediately turn itself into hot oily pieces over this...

[Rob Combs]

The machinist had cam bearings on hand for a fair price so I went ahead and replaced them. Will hold on to the other set for the engine the 2239 cam is going into someday.

So now we're back down to .0015 end play.

Now I have a question for whoever is still reading this - WRT to AA hypereutectic pistons and std iron cylinders -

I made my best attempt at measuring cylinder diameter and cylindricity

My most repeatable measurements yielded a minimum .0006" piston-to-cylinder clearance on the first piston I measured, ½" from the bottom of the piston skirt, then measured down the bore in 3 places perpendicular to the pin where the measured points would ride in the cylinder. Cylinder taper was ~ .001". Out-of-round was .01mm or .0004".

Although not very scientific, I tend to believe the piston to cylinder clearance because I can set the cylinder down on my desk, top down, and flip the piston over and drop it in, no rings, and it does not slam down onto my desktop - it sloooowly falls down the bore to the desktop, taking about two seconds or so.

I have not tried slipping a feeler gauge in there to verify but maybe I should have before coming to you for help. That said, here we are.

The .0006" piston skirt-to-cylinder just seems too tight. Would feel better at ~ .0025" - .0030". Since one is out of a proper clearance range, I didn't bother with the other three; they're all going in for honing to give them all proper clearance (and optimize the surface profile) if they're off.

Am I correct in my concern with the clearance?

And is this par for the course with AA pistons and cylinders? Or is my set way off in left field (in which case it does not escape me that in all likelihood I'm the one off in left field, maybe not my cylinder set!!)

If they're whacked out are the Mahle's better as a set? I read on here that the cylinders in the Mahle kits are AA anyway.

What are your experiences?

Thanks as always!

Rob

[modok]

You are correct.
I decided on .0025" clearance for AA's hyper slipper skirt pistons

Several years ago the aa thickwall 92 pistons were too tight
I emailed AA and told them I had .0005" clearance, even after removing the skirt coating
they recommended .002"
I told them I would hand file the skirts to achieve the right clearance
never heard back
Was that a joke or an actual tactic?
I plead the fifth

your measuring talents may be.... not yet at a professional level
But the ability of china to make a cheap piston the right size, can be worse than your abilities
So, you have the right idea
I would assume the coating is at most .0007" thick