Dave's Engine Build Questions - **Now Valve Geo**

[owdlvr]

Alrighty...here's my thread of engine building questions. (based on my 1776 build)

...questions that have come up so far:

1) On one head all the valve stems are equal height. On the second head both intake valve stems are .013" lower. Do I worry about that?

2) Head CC's - I've come up with the following when measuring my heads. (Empi pro-street heads) First off do these numbers sound about right (ie my method is probably correct)?  #1-50cc, #2-52cc, #3-54cc, #4-55cc. Do I compensate for the difference between cylinders (and thus the difference in compression) via deck-height or am I looking at removing material in the combustion chamber?

3) Ring gap - Ring gap is within spec for each, but varies on one cylinder. Three cylinders are .018" gap for the top ring and .017 for the second ring. The fourth cylinder is .018 and .019 (+.001). Not a problem, since it's all in spec?

-Dave

[Bruce]

#3 is easy.  No.

By itself, #1 would be No too. 
However, with the large variation in your chamber volumes, you can fix #1 and partly #2 at the same time, if the low volume chambers (50 and 52cc) are on the head with the intake valves that are high in the chamber.  By cutting the intake seats .013" lower, the chamber volume will increase.  Is the low chamber volume head the one with the stem height variation?

Either way, you must match the chamber volumes better than they are.

If the heads are untouched, I would consider returning them.  10% chamber variation is grossly unacceptable.

[owdlvr]

Thanks Bruce!

I'm going to measure the CC's again to confirm I did it right & make sure I'm being careful enough with my measurements, and then take it from there. Valve height variation is on the 54/55 head.

-Dave

[owdlvr]

Alright, haven't revisted the heads...working on getting the bottom end ready for balancing tomorrow. My plan was to measure the end play and deckheight tonight, but things didn't exactly go as planned.

First off, my Scat Flywheel doesn't want to mate up with my no-brand forged crank. Not overly surprised here, it does say made in China .  Each of the dowels is in the right spot, just appears to be a wee bit too tight of a fit. A light tap with the dead-blow didn't do anything, so I didn't bother playing around with it. It's going to a machine shop tomorrow for balancing, let them fix it!

Here's my "deck height"...I'm assuming I'm going to have to start with shims in order to sort these out? I placed one of my V-blocks across the piston and measured the height between the piston and edge of the cylinder.  1, 2 & 3 are 0.007", #4 is 0.008". Well, for what those numbers are worth. The cylinder's are just 'resting' on the case (couldn't torque them down without making something on the lathe, lathe is across town).





So here is where I get stuck...sort of. I figured after measuring the deck-height I would have a theoretical compression ratio and thus a starting point for a discussion on what I should be aiming for. But since I have to shim just to get the clearance Bentley calls for, I guess we should start that discussion now? Final build is a 1776 and I'd prefer to run on regular gas. I put 45,000 miles on the bug last year so overall life of the engine is more important then absolute power. What should I be aiming for, and thus what barrel shims should I be ordering to start with?

At some point it's going to come up, so here's the build specs:

- Mahle Forged 90.5mm pistons and cylinder set
- 69mm Forged and counterweighted crank (no name, cip chinese made)
- Scat i-beam rods
- Scat C20 Cam
- Kadron 40mm dual carbs (yet to be purchased)

Let me know what else is relevant and I'll post it up.

-Dave

[Bruce]

A conservative CR would be 8.0:1.  Then you can use cheap gas in cool weather.

You'll need to shim the cylinders up from the case a bit.  When you're setting your deck height, do not go with more than 1.5mm.  1.25mm is good.  1.0 is risky.  At that DH, you may run into the piston hitting the head.  The tighter the DH, the better the resistance to pinging.  I like 1.25mm for my use.  Lower reving engines with short stroke cranks can take less DH.  However, China cranks........

[owdlvr]

Alrighty then, a set of .060 shims should start me off in the right direction...at least get me to a point where I can measure something.

-Dave

[owdlvr]

So regarding endplay...

I've got the Bentley instructions, I've checked endplay on my engine every time it's been out in the past. Here's where I'm at with the new build...

Currently measuring with used shims, torqued to 200lbs for measuring. Forgot to order new ones but also realized that used shims would give me an idea of what I need to get. I put in 3 used shims which measure 0.0328". With all three in I have .015" of end play. Can I do some simple math to get a good guess on shim requirements? If so, without the shims I theoretically have 0.0478 of total end play, which thus should require .0448 worth of shims to get to 0.003". Closest I can get is with the three thickest shims which will get me to 0.005". Is four shims okay?

Do I aim for .003 or .004?

-Dave

[owdlvr]

Ended up getting it solved and set for .004". Local import shop had a stack of shims I could play with.

-Dave

[owdlvr]

Okay, really simple this time...

1) If you're looking at the top of the piston, and the arrow is pointing at 3 o'clock. How do I want to arrange the ring gaps? If it matters, I've got standard Mahle for the top compression ring, total seal rings for the second compression ring and standard mahle for the oil control ring. I understand the oil control ring gap is supposed to be at 12 o'clock, but which part is "the gap"? Am I worried about the upper ring segment, the lower ring segment or the expander? Mahle paints the portion where the expander ends join together...so that's probably a clue I'm missing.

2) So when building a stock 1600 I just run a bead of silicone around the cylinders. Whats the plan now that I have two sets of spacers? Put the spacers on the barrel, run the bead of silicone and trust it all to seal?

Ahhh yeah, stupid questions

-Dave

[Bruce]

1) It makes no difference.  The general direction is to put them at 120

[Geoff]

1) It makes no difference.  The general direction is to put them at 120

[owdlvr]

Thanks guys!

I ended up doing the silicone as suggested, but I didn't have heads to tighten everything down with...no worries, did one cylinder at a time and used the deck-height tool to tighten it down while the silicone set! Longest 6 hours ever...but I was doing other jobs at the same time. Stay tuned...my next questions will be Tuesday night after I try and sort out the valve train geometry

-Dave

[owdlvr]

Alrighty, had some issues with the valve train geo, spoke to Darren and picked up some Lash caps this morning to help me out.

As I understand it, perfect valve train geometry is going to end up being a compromise between the wipe area on the lash cap and the angle of the pushrod to adjuster. Here is where I've got it set currently, with no shims. The pushrod is an adjustable rod set to loose-zero.

Zero Lift:



Half Lift:



Full Lift:




wipe area, which I think is pretty spot on?

If I understand this correctly, for the pushrod side of things at half-lift, I would ideally want to add a spacer under the rocker shaft mounts, which should straighten the slight angle out that i can see in the photos. But doing so will move my wipe area up on the valve, and I'm pretty much centered right now. I *think* the valve side is the more important of the two, considering how close I am, so I should just stick with what I've got here. Correct?

-Dave

[Billyisgr8]

I would still put a .060 thou shim under the rocker shaft and see where it ends up.  You can use a regular washer if you don't have any proper shims.

Kevin

[Bruce]

What you have is no good.  The pic you have of full lift is what it should look like at half lift.