OK,

I know I'm not doing something right here. I have the "blueprint" of adjusting lash cold written by JohnZ and SWDuke. I'm at the point of my engine assembly where I want to adjust the lash cold using the settings of .021 Intake and .026 Exhaust. The procedure clearly says to start by getting TDC for the #1 cylinder. OK, turned the motor so that the piston is right at the top of #1 cylinder. Doing this will allow me to adjust 2 valves at a time; in this case, #8 Exhaust and #2 Intake. Only trouble is the #8 spring is compressed while the #2 is loose . I expected to have both of these valves still on the base of the circle and not on the ramp which engages the rocker down on the valve stem compressing the spring.

I know this is basic stuff to you guys. As I'm writing this the "light is going on". Maybe I should just turn it another 180 degrees???? (I'm thinking I'll still be in the same place as I am now). I'm writing this at work so can't go out and try this right now.

Appreciate your help!

Thanks!

Jim


[Modified by 6T5RUSH, 10:57 AM 6/8/2004]

 

Jim,
Remember, the cam rotates once for every two crank rotations. Sounds like you are at the right place on the crank but the wrong place on the camshaft - try rotating another 360 degrees.

If your timing chain cover is still off, make sure the dot on the crank gear and timing gear line up.
Brian

 

Hey 65- the easy way is to stick your finger over the #1 plug hole, and turn the engine over. Once you feel a pressure in the cylinder pushing on your finger, you are on the compression stroke. From there, turn the engine over unill the timing mark is at the zero position and you are at TDC for #1 on the compression stroke. This is where you will want to drop your distributor in as well. I assume when you had the heads off, you found top dead center with a dial gauge and confirmed that it matches up to exactly the zero mark on your balancer!?

Good luck!
Matt

 

Assuming the cam and distributor are properly installed when #1 is at TDC at the end of the compression stroke, the dist. rotor should be pointing at #1 on the cap tower. Rotate 360 degrees and #1 is at TDC at the end of the exhaust stroke, and #6 is at TDC at the end of the compression stroke with the rotor pointing at the terminal for #6.

When the term "TDC" is used, it is usually implicit that this is TDC at the end of the compression stroke, not TDC at the end of the exhaust stroke.

Duke

 

Allcoupedup: Yup, I mispoke about the revolution...should be 360 degrees to get there. Thanks! The timing cover and harmonic are in place. I have to believe my engine builder addressed the dot on the crank gear and timing gear aligning up. Will see him at the house tonight to confirm this.

Birdball/SWDuke: Thanks for clarifying the specifics to TDC...was guessing on that one! Matt, now you've got me a little worried...Nope, did not confirm TDC with a dial gauge while the heads were off and the balancer on (Put balancer on AFTER the heads were bolted down).

Thanks all. Can't wait to get back in the garage and do this! Boy, do I have an understanding wife!!

Hey Brian, how many miles you got on your rebuild? You've got be done, done, right?

My garage still looks like a swap meet but I'm making progress.

Thanks again all!

Regards,

Jim

 

Jim,
I have exactly 0 miles on my rebuild. In fact, I get to pick up the heads today or tomorrow. I purchased three sets "rebuilt" heads to find one that was good enough to use. I then had to add $200 to replace a cracked guide and bent valve (shipping) and get a new valve grind and some other misc. stuff taken care of.

An M20 should get here soon too and then I'll be cooking with gas! Yep, I have a swap meet too and clutter everywhere. My wife has been miffed the whole time but it has progressed to the point where I'm sick of it. Next time I'll plan and organize much better.


Did you change your balancer and/or timing cover? I went with a new timing cover w/tab and a new balancer but made sure they matched. When I compared my old balancer and old timing cover with the new, the difference was obvious.

Brian

 

6T5 -
Just a word of caution: There are a lot of engine buidlers out there who will align the cam and crank gears with the cam dot pointing down and the crank dot pointing up (dots pointing towards each other) - thinking that this is TDC on compression. I've seen many engine builders install the distributor in the #1 firing position with the cam dots aligned like this. Fact is, this is TDC on exhaust stroke: TDC on compression is with the dots both pointing straight up. Don't trust your rotor firing position to determine TDC on compression: check and verify yourself that the piston/cam is on the compression stroke. Then verify that the distributor has been correctly installed. Then set your lash...

 

Jim, when you're at #1 TDC, both valves for #1 cylinder will be closed; the other TDC position will have both valves for #6 cylinder closed. As Lars indicated, when the cam and crank sprockets are "dot-to-dot" (crank dot at 12 o'clock, cam dot at 6 o'clock), the engine is at #6 TDC, not #1 TDC.

 

Who really cares where #1 is. As long as the chain is installed correctly it dosen`t matter. Do each cylinder one at a time by watching the opening and closing of the valves. As the intake starts to close, adjust the exhaust and as the exhaust starts to open adjust the intake.

 

Hey Allcoupedup, know what you mean about chasin' her at times during the rebuild/assembly. I feel for you on your efforts to get a good set of heads. Sometimes it's the little things that nag ya too. Like, for instance, I decided to wrench on the engine mounts and 1 of the bolts was slightly different in the bolt head then the others. Torquen' 'em down, snap, sure enough, I snapped that odd bolt off flush with the block :mad Fortunately drilling out the center and using an "easy out" I got lucky and wallah..put the right bolt in..done with that. But, you and I know there's day light in the tunnel and it ain't a freight train (hopefully) coming our way. I did buy the GM replacement 8" balancer and my engine builder was able to find a correct timing cover (correct in the sense that TDC on #1 with the timing mark on the balancer at the "0" tab) is right on the money, and on the compression stroke. So I think the questions of lining up the dots posed by Lars and John Z have been answered with a YES, this was done correctly! Thanks guys!

It's interesting to note the engine builder came out to my garage and set the initial lash .021 Intake, .026 Exhaust. I showed him JohnZ's/SWDuke's approach but he was more comfortable doing it this way:

The firing order is 1 8 4 3 6 5 7 2. What he did (keep in mind this was set up for initial run in as I do plan on going back and checking/adjusting lash using JohnZ's/SWDukes' method) was this:

He wrote down on paper the firt 4 firing order #s: 1 8 4 3

and then listed the last 4 right below: 6 5 7 2

He turns the motor so that the balance timing line is at zero, confirming that #1 is at TDC on the compression stroke, then he adjusts both #6 valves. He referred to the valves he was actually adjusting as "#6's are rockin'"

Then turns the motor to #8 TDC and adjusts both #5 valves (#5's are rockin').

He continues this thru to #3 TDC, then

starts the same process for the last 4: 6 5 7 2

listing the first 4 underneath them: 1 8 4 3

Finds TDC of #6 and adjusts both valves of #1...etc...

Again, this approach will certainly get me close and will allow me to at least to do the cam run in b/4 checking/adjusting the lash cold using JohnZ's and SWDukes approach.

Onward to solids!!

Thanks again for your help here.

Regards,

Jim

 

Geez, the guy is clueless! Talk about convoluted logic...

At TDC on the compression stroke the cylinder 360 degrees away in the firing order is at TDC of the exhaust stroke and both valves are open. What he did is just adjust both valves at TDC of the compression stroke, but this WON'T WORK if the cam is not on the base circle. In the case of the LT-1 and 30-30 cams they are NOT - exhaust with LT-1, BOTH in the case of the 30-30 cam. Adjusting both valves at TDC of the compression stroke is okay for the Duntov cam.

Just because a valve is "loose" doesn't mean it's on the base circle Your actual exhaust valve clearance is about .003" looser than what was measured!

I have yet to find an "engine builder" who really understands cams at an engineering level. Same applies for a lot of other internal engine issues.

As a point of reference the LT-1 exhaust lobe from the beginning of the opening ramp to the end of the closing ramp occurs over a total of nearly 540 degrees of crank rotation. The opening and closing ramps both measure about 110 degrees of crank rotation. The 30-30 inlet lobe is about the same, but the LT-1 lobe (beginning of opening ramp to end of closing ramp) is about 460 degrees.

Duke


[Modified by SWCDuke, 10:54 AM 6/9/2004]

 

they never learn,

 

Hey Ironcross,

I'm learnin', really, I am!! Thanks!

SWDuke,

From what you walked me through here (and I know you've covered this MANY, MANY times (for me, repetition is the mother of knowledge.. ) I'm beginning to have a hint of understanding on the exhaust adjustment.

So, I need to simply follow yours and JohnZ's guide and go around the motor adjusting just the exhaust valves to take up that extra .003 built into this first adjustment. Instead of lashing @ .026, I've got 'em right now at .029.

SWDuke, I know you're zeroing in on my engine builder's specific knowledge of the LT1 and the fact that he very well did not "grasp" the exhaust push rod was still on the ramp of the cam lobe when he did this exercise, but he definitely is not "clueless" in assembly and, frankly was quite thorough in this whole engine build process. He really took "ownership" of my motor rebuild. I do appreciate this critique. 'Nuf said.

Thank you again!

Onward to solids!!

Jim


[Modified by 6T5RUSH, 11:43 AM 6/10/2004]

 

Follow the procedure in the document and set the lash to the specs listed in the document for the LT-1 cam.

The inlet will probably be at the .021" spec but the exhaust valve will likely be about .003" loose relative to the recommended spec of .026", assuming he set them to .021/.026 using the procedure you posted.

Duke


[Modified by SWCDuke, 11:11 PM 6/9/2004]

 

Hey man, don't sweat it too bad. I too installed the LT-1 cam per JOHN-Z's procedure. After initialy setting that #1 at TDC it's simple to follow. I did 2 things, I first set the #1 at TDC, then marked my Harmonic every 90 deg's. I would do both to make sure I was as close to exact as I could by watching the valves, then referring to the balancer to see that my balancer lined up on the marks after every 90 deg rotation.

 

Easy to set the lash. I had never set solids before. But just followed John and Dukes settings for the my 30/30 cam and used a cloth tape measue to mark the balancer. Once their set they are great. I almost wanted t do it again just to get it dowm perfect. There is amother world above 6 grand.

 

65stinger/tuxedo/SWDuke,

Well, set the balancer @ TDC for #1, balancer @ zero on the tab. Followed JohnZ's/SWDuke's guide and marked the balancer @ 90 degree points and proceeded to do just the exhaust valves. Sure enough, I took lash in noting the rockers were all looser (aint' my grammer great ) then the .026 guage allowed. I adjusted all of them to "tight" .026. Did the rotation once more to double check myself. Frankly, it was pretty straightforward.

"Lights are getting brighter here".

Thanks again all.

I'm anxious to keep on "keepin' on" in this assembly and install. I'm looking forward to droppin' the distributor in (the anticipation of firing her is growing). I've got to be out of town over the weekend (my oldest grandson's B-Day). Kinda lookin' forward to seeing him and the family. Once home I'm off to Ypsilanti for a Finance conference all week. In light of what's goin' on in my garage, I am definitely not looking forward to being away all that week. Looks like next week end is my big wrenchin' effort.

Stay tuned!!

Jim

 

Where can the "blueprint" of adjusting lash cold written by JohnZ and SWDuke be found? I was hoping to check the lash on my 1964 327/365 30-30 Duntov cam.

 

You've got mail

 

JohnZ- Thank You