Been a while since I've been here. Trying to help a buddy get his 73' Camaro 350 running. It has a newly rebuilt stock engine that just won't run right. It has low vacuum (10-12") runs really rich and down on power. Switched carb and ignition parts=no change. The only thing we can think of that would cause this is that the cam is in wrong. With the #1 piston on TDC using a combination vacuum/pressure gauge in the spark plug hole and watching the rockers, the timing mark on the dampener was 12 degrees away from TDC. No amount of dizzy adjustments could get the vacuum up much over 12". Are we on the right track with the cam timing or could something else be wrong? I'd hate to pull the front of the engine apart if it could be some other problem.

Thanks

 

Do a compression test. If the cam is off, the cranking compression will be way out of spec for the engine.

Mike

 

We ran a compression test and all checked between 140-150 PSI.

 

I have a ’69 with a CE 350 engine in it. Console plate says it was a 350/350 11:1 but I have no way of knowing for sure. Your description fit it exactly; ran too rich, power not so great, fairly low vacuum. Replaced the plug wires – and didn’t note the order they were in before I did so thinking it would be the standard firing order. Couldn’t get it started at all, backfired through carb. Followed the GM Service Manual to reset ‘disturbed distributor’ – I was getting plenty disturbed. I had heard about cams being 180* out and sure enough that’s what it was. Followed the same procedure but instead of setting the rotor at #1 I set it at #6. Put the wire for the #1 spark plug there and followed the normal firing sequence. Started right up.

Compression shows a solid 215psi per cylinder which makes me think it may have been the 11:1 motor that got rebuilt. It’s clean and tight. Somebody goofed on a rebuild who knows how long ago. After that it was all about the carb and getting it set correctly, making sure the points & vacuum advance are working etc. Setting the idle mix screws for max pressure the best I can get is 10Hg @ 650rpm assuming my 40 year old gauge is accurate.

So here’s the weird thing that I hesitate to mention in this forum – timing – because it’s usually a hotly debated topic. I think that because the cam is 180* out it means that the relationship of BTDC and ATDC are reversed on my timing tab. Whether they a really are or not I don’t know but it seems that way based on the symptoms. Trying to get my head around what’s going on makes my head hurt so I just concentrated on finding where the car likes to run rather than exactly why.

I ran through the range from 10* BTDC to 0* TDC on the timing tab and it ran like crap – very much like you described. It did run though and these things can be very forgiving in that regard.

After endless experimentation I have it set right now at 6* ATDC per the timing tab. At 4* it still pings at w.o.t and at 6* ATDC it runs nicely but seems a hard start sometimes and diesels slightly. As soon as the replacement for the broken stupid little retainer clip for my accelerator cable shows up I intend to try and sneak the timing somewhere in between 6* and 4* ATDC. I have to adjust the master idle each time I change the timing because this thing seems to want a low idle.

Again only based on what the timing tab says not what it actually might be I expect this thing to run and drive decently based on what I’ve already found. I’m down to small final adjustments. Makes plenty of power, doesn’t run hot, idles at a nice low lump-lump. A very slight bog off idle but that’s another can of worms I have been fooling with. I may replace or rebuild the Holley 4160 but just want to use it the way it is this summer rather than chase perfection.

I know this isn’t exactly what you are talking about or if any of it helps – but I have a sbc 350 running at fairly low vacuum and it’s doing ok so I don’t know if that’s the issue or not for you.

Good luck

 

pigfarmer, thanks for the reply.
I just went through this same thing on a flathead 6 in an old ****** truck. This engine started easy, idled well but had low vacuum (10-12") and ran rich with low power. After looking at pictures I took during my rebuild and help from the internet, we discovered that I installed the cam 180 out. Pulled it apart, corrected cam and life is good now. Has plenty of power (relatively speaking!) and 15-18" of vacuum.

We'll try your plug wire swap and see what happens. Will report back tomorrow.

Thanks

 

is the damper old and the outer ring has slipped?

 

Cool.

On that old flathead - does any of the stuff about BTDC and ATDC on the timing tab sound familiar to you? Just curious.

thanks
Jeff

 

Dampener is new.

 

My tired old brain is having a hard time with the whole cam timing thing, but what you said makes sense. BTDC and ATDC reversed. I think the only way an engine can run with the cam not installed correctly is if it's 180 out. Anything else and it wouldn't run at all. Anxious to try it out.

 

This may not make sense to some, but... The cam can't really be '180 out'. On one revolution of the crank, the timing dots on the crank and cam gears will both be at the top. On the next revolution, the crank dot will be up, the cam dot will be down. So on every other revolution of the crank, the cam is '180 out'.

I would be more inclined to check that the distributor is not a tooth off, or there is a vacuum leak, or you have the incorrect timing tab on the timing cover.

DaveZ.

 

If you actually put the #1 piston at TDC and the timing mark was out then the balancer has slipped or you have a bad balancer and timing tab combination.

Make or buy a piston stop and use it to check TDC. Watching valves and measuring pressure in the cylinder is not accurate enough to be of much use.

The only way to know the camshaft is out (say by a tooth on the timing chain) is to degree the camshaft. You have to first know the TDC timing mark is correct and then use a dial indicator on the lifters and compare the readings to the cam card.

You should also check that the rotor in the distributor points to the #1 spark plug when the engine is at TDC with the #1 cylinder just finishing it's compression stroke. Both #1 cylinder valves should be closed.



It may be contested but it's impossible for the cam to be 180* out. There is nothing to debate because anyone who says a cam can be installed 180* out is wrong, period.

It's also impossible to install the cam 180* out so BTDC and ATDC are reversed on the timing tab. With the standard engine rotation, before top dead center always occurs before the piston reaches top dead center. The engine would have to run in reverse for BTDC to be on the other side of the pointer or you'd have to swap the generally well accepted definitions of the words before and after.

What you described about changing the distributor was because you (or someone else) installed the distributor 180* out, so it was pointed to the #1 plug when the #1 cylinder was at TDC on it's exhaust stroke and the #6 cylinder was at TDC on it's compression stroke. This has nothing to do with the cam being installed 180* out, which once again is impossible. I have no idea why you had to set the timing goofy, but it was likely because the balancer and timing tab were out and not properly indicating TDC.

 

OK, played a little more and as lionelhutz said, swapping the #1 wire position to the #6 position didn't work, wouldn't even start. So it seems pigfarmers dizzy must have been install wrong by the PO.
What we did find was a noisy lifter. Set the adjuster nut like it says in the manual started it up and it was initially quiet. Then after a few minutes it started clicking again. It's an exhaust valve. This is a problem, but I don't think it is root cause of the low vacuum and right mixture. Agree??

 

didn't think so since it was running before

as for the rest ... see what I mean ?

 

A loose exhaust lifter will cause it to run badly and does affect vacuum. You probably need a new nut on that rocker arm. It could be the lobe wearing down but it shouldn't wear down enough to go from tight to loose again quite that quickly.



See what exactly? You don't expect responses telling you that the completely wrong info you posted is wrong?

 

OK, I’m no mechanic my statement may well be wrong as is something else with the way the motor was rebuilt. I methodically went through my problem by myself with a GM service manual and have the car running nicely. I simply shared what I did rather than tell anyone anything.

There are many ways to say something and the pedantic nature of your response reveals more about its author than the topic.

 

He is not being pedantic. Wrong information needs to be commented on as others may read the thread later. We don't want someone tearing their engine apart for no reason because they got wrong information here.

 

The engine now seems to have an oil leak from the rear main area. This engine has valve train issues and oil leaks so it's probably best to just pull it from the car and start tearing it down. This engine was built by a 3rd party, so we don't know what was used for the rebuild.
But before doing that, we'll cut the oil filter open to see if there is any metal in it.

 

Agreed. I'm not going to coddle information that is 100% wrong and written like it's a debatable fact. It'd be really sad if someone pulled their engine apart thinking the cam was 180* out.

 

One thing that seems to always to frazzle a novice wrench is the fact that there are three different timing tab positions for a SBC from the factory....this can trip a person up horribly.
The best thing to do if you are not sure is to do the piston stop as suggested and find true TDC.....now where is the balancer at reletive to the tab? It needs to be at 0....anything else and you are shooting yourself in the foot.

Another common problem is leaky intake gaskets......this will give low vacuum as well as an unstable vacuum....
Go around with an unlit propane torch and fog the gas around the base of the intake.....look for idle change. See if your intake bolts are loose as well just because you can

Post your finding.....good luck!

Jebby

 

Actually I thought what you said was very interesting and had no intention of debating. This forum is hardly the only place that topic has come up and that's why I said I was reluctant to mention it. Also, the thread was started by someone else and this has since hijacked it.

At no point did I 'rip my engine apart' and wasn't even suggesting that anyone do. If a person is foolish enough to go tearing into something based on advice from one thread in an online forum they deserve whatever comes next.

Since other have brought this up - I am well aware of how to find TDC and it agrees with the timing mark. OK, a cam can't be 180* out. A little Googling will show you why I said it was debatable and this is hardly the only place it's been brought up. Something else is screwed up and I seem to have found a simple workaround.

My car now runs nicely with no issues and I didn't need an anonymous forum lecture to get it that way. One day maybe I will have reason to pull it and find out why but not the way it is now. Maybe I'll just leave my laptop down in the garage so you can have a closer look.

It was the way you wrote it I didn't care for, not the information itself. Others replied and I appreciated it - but I found your writing style to be obnoxious. Being right doesn't mean you can't be polite.

Naturally you won't see it that way so over & out. Done with you and this thread.