76C3forme

Hey everyone,

I wanted to get a little confirmation from some others on the board. (so I can verify I'm not going senile!)

You know... Technology is nice, but going back to "old engines 101" after awhile, you get kind rusty.

I have a question about a coworkers car that I had the chance to look at over the weekend. Here's the story:

It's a 1979 with an L-82 / 4-speed from a 76. Since "my new C3 find" is a 76, it's made it easier to "verify things" about the powertrain etc. He's had this stalled project for quite sometime. Body is just about ready for paint but he's had an issue since the engine was rebuilt and I wanted to get a few opinions.

I seem to think there is an issue with improper Valve timing / possibly chain installed incorrectly (possibly by a tooth / possibly retarded).


1976 L82, 4 speed
Rebuilt a few years back. Block, crank, pistons, machine work, cam bearing etc done by a local machine shop (great reputation).

Heads - 3973487 2.02 / 1.94 75cc 72 LT-1: CURRENT OWNER REPLACED the rebuilt the heads(Also done by a very good shop) , intake, carb, timing chain, exhaust etc..
Comp Cams 1.6 Ratio Rockers
Comp Cams 268H Hydraulic Cam (Spec here) :

http://www.compcams.com/Company/CC/c...x?csid=73&sb=2

Edelbrock Performer 1406 Carb (650cfm Mech Secondaries)


After he reassembled it, he was having some issues with low Vacuum at idle (7-9HG at 900 RPM). He "compensated for this" by setting initial timing at 16-degrees BTDC and idle at 1300 RPM (manifold vac increased). This most likely put his timing "All in / 36-degrees pretty early.

He ran the car this way for a few hundred miles, tinkering with it here and there. "Guessing" / being told, that the low manifold Vacuum is due to the "performance cam". ....

(Well, I mentioned to him that "for reference", I have the 270H Comp cams in my current L-82 with a similar setup / 1.6 roller tip rockers, holley 650, and I'm getting about 17-18" of vacuum at 1000, rpm) . I've used the 270H and 292H on numerous small block chevy street engines (about 4) and have always had pretty good vacuum.

After speaking to him at the office "off and on" I went out and took a look at this thing last weekend. This is what I verified / did.

Set initial timing / idle "to the sticker" @ 12-degrees BTDC @ 1000 RPM (pretty much what my car is set at). Now that I had a "baseline" I checked manifold Vacuum. 5-7HG (fluctuating / not rock steady) @1000rpm. What...! I checked his gauge on my truck and pulled 20" @ 900rpm so the gauge is good.

Spark Plugs - AC R45TS. Reset to .045 (A little "dark" but I was really surprised to seem that this "decent looking - not tan obviously but not horrible either)".

While the plugs were out: Rotated the engine to TDC (Balancer is accurate). Distributor is right on. I say to him: "Hey, while were here", just pull these valve covers, and let's make sure valve lash is correct.

Valve lash. I usually don't "spin" the pushrods and feel for the drag. I use the "up and down method", and when there is no movement, I use 1/2 to 3/4 of a turn. I've done this a million times so I'm not going to make the post any longer with the procedure. Lash is good. I set valve lash , rotated around , rechecked, (As a note: the lash was a "tad loose" but nothing that would cause issues previously).

Next I pull my compression gauge, tell him to go get a few beers, we're going to take a 1/2 hour more and make sure we don't have issues

Compression Test Readings: 1-168psi, 3-168psi, 5-167psi, 7-169psi
2- 167psi, 4- 169psi, 6- 167psi, 8-168psi

So they are looking good.


Replaced valve covers, Fired it up. Sounded better. We're now at 7-9HG @ 1000 rpm. Way to low for this cam, that's for sure. NO smoke out of the tail pipes. the "slight eye watering" we were getting previously he immediately noticed was not there), but still. This isn't correct.

While it's running, I spray carb cleaner (again) everywhere. No leaks from Intake, Carb, Carb base, Brake Booster / Hoses, vac advance canister , nowhere.... etc.

Intake: Performer with EGR Plate Blocked.

Distributor Stock HEI. Advance weights moving / free , not stuck. (HEI looks brand new - as does the entire engine.). I didn't think we were having an ignition timing problem - but figured I do a quick look.

Vac advance line is hooked up to the Manifold vac port on carb. Timing now at 12-degrees BTDC @ 1000rpm (with vac advance hose removed and carb port blocked of course).

So . . ., I've got laminated plastic sheets with Vac Gauge Readings, troubleshooting, notes from years ago, with different issues etc. In 30+ years of working on cars, using a vac gauge has always been a HUGE help to diagnose things (always amazed that some don't use them).

Anyhow..., based on all of the info I have here, and everything I've seen over the years, I keep coming back to my same "response" that I gave him when he asked me a month ago:

Low vacuum in that range with the symptoms that he's having has mostly always (for me) turned out to be an issue with VALVE TIMING.

Here's the thing though: In my notes, I've run across 3-4 of my cars / friends cars with similar low 5-10HG vac readings and with the exception of 1 car, it's always turned out to be some sort of valve timing issue. (Jumped chain or a chain that someone installed a tooth off) etc.

One car, I actually found it to be an intake manifold vacuum leak INTO THE LIFTER VALLEY which did not "show up" when I was doing the old carb cleaner trick.

However, the thing that is stumping me is his Vac Reading. Normally, I'd expect it to be more "steady and low" . The 5-7HG or 6-10HG give or take now, seems to me to be a valve timing "thing" BUT it's fluctuating between the 5and7HG, (now 6-9 / maybe 6-10HG). I don't seem to remember this in the past (or in any of the info that I have here).

Right now. Compression is good. Lash is Set, Ignition Timing is fine. Idle is in range, No visible Vac Leaks. (even disconnected brake booster).

ALSO, Bumping idle to 1500 or so (like he did) and vac is right up into the 17-20HG range.

When Idling high, a "quick blip" of the throttle, see a normal drop in vac to 5hg or so , then a spike to 20hg or so and then back down to 17-20 - so at "a higher idle" it does seem to "even out a bit" - but it's still not correct.

I almost thought about some kind of "incorrect valve spring" issue or something like that, but I'm just not "seeing that". I think Manifold would be higher but then fluctuate quickly on the "bad cylinder".

I still think this valve timing (retarded). Any other tips?? I've soaked down the exhaust bolts, and I'm going to go over this weekend, pull the oil pan, balance, WP and timing cover and check just to be sure.

Anyone else go through this? Any help is appreciated.

Recap:
L-82 - 4speed, 9.5:1, Comp Cams Magnum 268H, 1.6 Roller Rockers, Valve Lash Set, Timing 12-degrees BTDC @ 1000rpm, no Vac Leaks found, Ignition / HEI / Static - Ignition timing all good. Edelbrock 1406 650cfm Mech Secondaries (also no leaks, throttle plates and choke set correct).

Compression test = Good (168psi on all pretty much). Also. No appreciable Leakdown overnight.

Currently 7-10HG of Vac @ 1000 RPM idle. (Fluctuating between 7-10HG not steady). Raising Idle can achieve 14-15HG of Vac.

I still suspect Valve Timing, but something with the vac reading just strikes me as odd, I think it would be more steady..

I'm rusty. Any info would be huge help. Especially if you've had these same symptoms. Pulling the timing cover isn't a big deal and we'll most likely do it anyway to check thing out but confirmation would be nice. Thanks.

Jebbysan

I suspect a leaky intake manifold for two reasons.....
The needle is not steady.....
And it spike to 20 then falls off after you blip the throttle....when you rev it...it has sufficient airflow to overcome the leak. that is why it increases and smooths out.....
The intake leaking in the lifter valley like you say is not easy to pin down.....but go around and see if the bolts run down.


You can check the timing via dial indicator vs. the mark on the balancer, at the rockers....but I would just pull it apart and verify the mark on the cam gear is where it needs to be.....although I doubt that is what it is.

The bouncing needle gives it away......you should have 12-13 inches of vacuum with that cam.

Jebby

76C3forme

Thanks Jebby. That's what I'm kind of going back and forth with.. I keep getting stuck on a Valve timing issue BUT,. the fluctuating needle is what's "odd" to me (like you mention). I would expect, it would be low and steady and not low and fluctuating.

AND, since I've only had an "internal" manifold leak in the past (and I didn't keep very good notes), I'm wondering if this is the symptom that I had in the past on a friends engine but "failed" to really document the reading.

I also notice that if I remove a vacuum plug from a plugged port on the intake, I get a rise in idle (but that would seem normal to me).

I think (like you mention) the fact that I can achieve a much higher vac reading with a higher idle seems to "sway away" from a valve timing issue.

I threw my degree wheel and dial indicator into my bag for this weekend already. I think maybe I will pull that intake as well for him. Maybe I'll do that first..

Jebbysan

You are very thorough.....
Like I mentioned....run a pattern on the intake bolts....
It is very common for some to come loose after heat cycling.

Jebby

76C3forme

Hey thanks, (sometimes so thorough, I drive myself crazy!).

One question for you:

Normally I associate an intake manifold leak with more of a "Lean looking spark plug", but in this case, (although they look "ok", they seem to lean toward the Richer side). Do think it's possible the leak may be more "in the valley" as opposed to leaking from between the intake and heads? Just thought I'd get your opinion on that.

One thing that may be throwing me off is: These plugs have been in there a long time AND he did have it pretty advanced. I'm wondering if they could have been "blacker from him running it that way), but since I how have timing / idle back in the ballpark, I'm wondering if they would eventually appear a bit leaner if it was run for any extended period of time like this.

Once we get thins thing sorted out, I'll throw in some new ones for him. (I never like to use a plug if its been or possibly been gas fouled).

Either way, I think you now have me leaning more the intake route as well. I'll torque that down and see if anything changes.

Jebbysan

Yes...in the valley is very common...and the black on the plugs can be oil vapor being sucked in from the bottom....

Let us know what you find

Jebby

76C3forme

You know what? That's what I'm TOTALLY missing. (and most likely why the "darkness" on the plug isn't "sooty" . I bet it is more "oily". I wish I had one here right now.... (He ran some seafoam a little while back and I wasn't so concerned about the plugs since they did not appear to be that bad. I know they get a little slick after a bit of seafoam. I'm betting that's a slight oil misting / darkening just like you describe..

I'll keep you posted. (Maybe this big block Olds guy with remember some of this SBC stuff after all....

427Hotrod

Harold Brookshire's (Ultradyne Cams- Designed your 268H and the Voodoo series also) Quick N Dirty' method to ck if cam is installed correctly:

1.---Pull off the driver's side valve cover. Turn the engine to TDC, and ckeck #1 cylinder's valves. If both of them are closed, you are at the ignition point. Turn the engine over 1 time, back to TDC, and both valves should be off the seat.

2.---Check the height from the top of the retainer to the spring seat, first on the intake, then on the exhaust. I recommend something like a Machinist's 6" steel rule. Make sure you wrie them down, because you need to see which one is closest to the head.

3.---If the cam is in the engine right, the intake retainer will be .030" to .060" CLOSER to the head than the exhaust retainer is. If the cam is retarded, the exhaust will be closer.

This happens a lot, and a sure giveaway is very rough idle, very low vacuum, needing a lot of ignition advance to run, and coming alive about 35 mph.


JIM

76C3forme

Hey Jim, Thanks,.. This is why I wanted to post to the forum to get some additional opinions. It's been quite a long time since I've been troubleshooting a SBC with an issue such as this. It's those little things like you and Jebby have posted that are a huge help.

Not that it doesn't happen with the Olds Engines I'm more familiar with, but the "kind of common" intake leaks at the manifold and the "little tricks / specs" from guys who see this all the time are a huge help.

I've seen quite a number of SBC's where the chain simply was on the "mark and not the dot" just as you mention. (or worse!). So I guess that's why I began leaning toward that conclusion.

I'm going check exactly what you mention as well as the intake as Jebby suggested. It should be one of those. In fact, perhaps it has both of these issues, making it a bit more challenging . I'll keep you both posted.

One thing though Jim. I may be incorrect, but my experience (from what I can remember) would be that the vacuum would be low (of course) but more "steady" / limited / slight fluctuation with a valve timing type of problem. Maybe I'm being to critical on that. . In my case, I have a pretty good amount of fluctuation and that's what was striking me as odd. (Even so, I was still leaning toward a valve timing issue). After reading Jebby's posts though, I started to kind of lean back the other way.

I think one or both of these tips are going to do the trick either way though. I believe (hopefully) I've / We've narrowed it down.... Like I said, I now wouldn't be surprised if there was possibly multiple things going on.

drwet

Very interesting puzzle. You obviously have the skills to figure it out, and I will be very interested in the solution.

I have had a vacuum leak at the intake manifold gasket, and while it gave me fits trying to figure it out, it did not behave the way you are describing. I had decent vacuum (and I have a little more cam than you do) but rough idle. Doesn't sound like what you have.

My guess is you were right the first time. I would check to make sure the cam is a) installed and b) ground correctly. It wouldn't be the first time the cam was not manufactured correctly.

76C3forme

drwet,

Yeah, this one is just a bit odd to me. I can't say that I've seen this exact symptom(s) before.

I'm not a mechanic, so it's not like I do (or have done) this everyday. I've built about 4 Olds Engines, 3-4 SBC's and a few Ford small blocks, I've had 2 track cars and 4 Buick Grand National's / T-Types so I'm familiar more recently with the SFI 231 Turbo V6's. (not that you couldn't have the same issues on those engines either...)

For a "change of pace", about 10 years ago, I got interested in the Jaguar V-12's. (I still have my 1990 XJ-S Coupe). Boy, talk about some over-engineered / crazy stuff there!

I think being able to "put them together, blow them up, and put them back together again is a big help,. and I've always been reasonably good at troubleshooting, but since I never did a lot of "day to day" work repairs, it takes me awhile to go through something that I'm not familiar with / haven't seen before.

Especially on something like this when it's (to me) a little less "textbook" of an issue. But, I just do what I always do: Knock out 1 item at a time, record the results and ask questions. There shouldn't be much left... (hopefully). Looking at the specs, the build quality, parts etc, I know there's a good running small block "under there somewhere".. We just have to find it.

Thankfully, I still have ton of Chiltons, and Haynes, and GM shop manuals and diagrams etc, and of course it's soooo much nicer now (compared to the good old days) that we have a lot of great forums with a lot of great info.

It's always tough to jump into somebody's project "cold" / with no history. Like I told him, sometimes a 2nd set of eyes and starting from scratch is a big help. I think he looked at this issue for so long, he's just "stalled / got a mental block". I think we'll get this going for him and it will give him the last burst of energy he needs. I think once it's running and healthy, he'll finish off the body...

gungatim

After you verify cam timing with your degree wheel, check for a sticky valve.

here's a handy quick guide I use for vacuum diagnostics. forget where I got it so apologies to whoever I copied it from.

76C3forme

Hey thanks gungatim,

I guess I must qualify now (at 48) as an "old fart" like the chart says.

I have a few charts with Vacuum Gauge readings that basically indicate the information on that list. (as well as some other detailed info). They are a huge help. Much like the list you have there. A vacuum gauge is a great tool for sure.

The thing I "normally" expect with a sticking valve is a lower but fairly steady vacuum reading (maybe in the 10-15HG range on a car with a normal 17-18" of vacuum for example) but with a fluctuation of about 2-5HG with kind of a "rhythm" to it.

(Although in my case, I still really couldn't rule out a possible sticking valve on multiple cylinders giving me a more rapid fluctuation). And, with an engine that may have a normal manifold vacuum in the 13-15HG range, I certainly expect to see something close to the actual reading on this engine.

I'll keep everyone posted. It's nice to have several sets of eyes on something. For sure.

gungatim

yeah same here but since you said he re-did or replaced the heads, mistakes could have been made there.

also I didn't scroll up to re-read your data but did you do a leak down test? could have good compression but a leak down would help identifying as well.

also got a stethoscope? listen to each cylinder and see if you hear anything odd, or listen to hear anything odd, however you say it.

76C3forme

hey there,

Yeah, the leakdown test looks just fine. ( I think I put that in the recap at the bottom of the post but may have neglected to mention that "up top". I agree, the shop the did the heads is very reputable / been around for ever, but that doesn't mean a mistake could not have been made. I should throw the stethoscope in the bag just incase. Thanks.

Jebbysan

Great info.....bookmarked

Jebby

gkull

Jim gave you a nice check idea. But instead of all the dorking around it would have been quicker to just take the timing chain cover off.

76C3forme

Well, I don't know.... You figure, (I'm not in front of it), but you figure:

Normally I'll pull the Y-pipe off (he's got a 2-into-1-back into 2 stock setup). I've been lucky will dropping the pan enough to at least remove the timing cover, BUT, I've also had some pretty crappy oil pan gaskets stuck to the oil pan and engine, that I then had to remove, clean and replace under the car because the exhaust bolts / hardware were so darn rotted, rusted and rounded, that I'd then be pulling off the manifolds, re-tapping the studs etc. ( He's a good guy, but I'd like to not "go crazy" and start reworking the exhaust now as well! )

His car "should" be a bit cleaner but if it wasn't, I'd probably use Jim's Tip so I didn't have to "open up a possible can of worms".

I agree with you though. I would normally, (especially in a situation like this where I just don't know anything about the engine) remove Exhaust, Oil Pan, Balancer, T-Chain cover / the whole ball of wax and that way we know exactly where we stand.

I do want check out that intake again though before I start digging into it, just to play it safe..

76C3forme

Hey guys,

So today, I wrap up a bit early and shot over there to look at the car. Even though I didn't plan to work on this thing tonight (nor did I . . . pretty much). I wanted to post what I found.

I didn't have all of my tools but did throw the torque wrench in the car last night just in case I had a chance to run over and re-torque those intake manifold bolts.

I totally forgot the performer intake he's using (like mine) uses the torx fasteners for the center 2 bolts on each side of the intake, He didn't have any large torx sockets so instead of torquing everything down and "feeling 30lbs/ft with a suitable Allen Key that he did have, I decided to wait until the weekend when we have time and I have my tools.

What I did do: Removed the carb and checked about 6 bolts (First 2 fronts on each side and the 2 before the end bolts on the back side).

After feeling how loose the first bolt was, I kept backing down the torque wrench until I got a reading. Looks like 20lbs was the maximum torque I found on the ones that I checked today. 1-2 were more like 15'bs.

I was able to use a 4" hex allen key by hand and the torx bolts I would estimate no tighter than 20lbs (being generous) based on "feel" / by hand.

It's odd that I have no leaking between the intake / gasket and the cylinder heads / vac leak from the top, but based on the fact the the engine has not been run that much after rebuild, I'm guessing that the intake gasket still has some "thickness to it" and is sealing up top fairly well.

I'm thinking (like Jebby said), after break-in and a bunch of heat/cool cycles, this has never been checked, re-torqued.

So here's the thing: Do I re-torque the intake, put the plugs back in and give it a quick "fire up" and see if my Vac at idle has changed just for the heck of it?

OR, (since I don't know how long it's been like this, do I play it safe, replace the intake gasket for him (he's got a brand new one that came with the engine kit from the builder and he purchased a second since he installed the intake so he does have it lying around.

I tend to say torque it down and see where we stand. I'd think, it should be fine. If it's hasn't been re-torqued, I wouldn't think it would be compromised in any way.

I'm also temped to just check the timing chain so we know for sure, but I'm thinking , maybe just re-install plugs, carb, re-torque and give it a shot.

Thoughts??

427Hotrod

I'd fire it up and see how it does. I've never used a torque wrench on an intake in my life....pull them suckers down! Maybe I have a "calibrated" elbow...but you can tell when they are tight.

Was there any oil showing in the ports? If there's a vacuum leak along lower side of intake it's going to pull oil into the runners. Was it dry or oily inside? Was it real sooty maybe?

Worst that can happen is you have to pull it.

JIM