Technical advancing cam questions

This should be any engine. Advancing cam 4 degrees with a 3 keyway sprocket.
1. Do you have to readjust valves?
2. How do you check valve clearance with engine together ?
My thoughts are just rotate cam until 4 degree adv. mark is pointing straight down.
Unhook chain and rotate crank until the same mark lines up with it.
Then put chain back on. I should feel or hear valve hitting piston when I rotate by hand.
Your thoughts?

 

You’ll need a timing set that allows different positions to start with.
You can’t just rotate a cam.

 

If it's an aftermarket cam it might already have advance built into it when you install it straight up. Good luck.

 

1. on initial assembly and time to time, because the cam has been advanced , no, but not too many people pull and engine down to fiddle with that,it should be done when assembling, or on advice from someone that knows better than mere mortals.
2. What engine?, what cam?
advice on assembly may follow when people know what engine! this sort of work is not always the same for every engine.

 

Not without using clay to check clearances.

 

Either a lot of risk or a lot of work for maybe a bit more low end. Use soft valve springs and a dial indicator, turning the crank 10* at a time and depressing the valve. You need about 0.080" for the intake. You are getting further away from the exhaust, so ne problem. Honestly I wouldn't even start
w/0 degreeing the cam per cam spec

 

o.k. so it a 350 chevy. Cam installed straight up. I have a 3 key sprocket set. So I want to advance it.
I align cam advance marker pointing straight down. I install crank gear so advance marker points straight up.
That should advance cam 4 degrees. I would start with engine on top dead center.

 

Trying to make cam seem smaller . I don't want to change cams. Just want a little more low end power. It builds power past my normal cruise rpm.

 

Here is my take on the subject. I have done it on a Jaguar XJ6 engine and was happy with the results.
If this is a standard compression 350 Chev there are a lot of cams available. As mentioned the change in lift to piston will only really effect the inlet cam. You should be able to work out how much extra lift the four degrees achieves as the piston nears the valve. If a commonly available cam is supposedly a drop in replacement and has similar lift numbers at this point you should have no issues.

Steve

 

I wouldn't attempt it without a degree wheel. I also wouldn't attempt it without pulling the head and checking piston-to-valve clearance as well. In fact, I probably would just live with the cam as it is. What are the cam specs?

 

Measure the lift at valve tip that happens in those four degrees and compare to the amount that you can push your valves further before they hit the piston at overlap TDC. If those four degrees are at least 0,05" less than the amount needed to hit the piston, you are good to go. Be careful though - due to the angle of the valve to piston, the valves edge might not be anymore where the valve pocket in the piston sits. With a boroscope down the inlet you might be able to look for interference possibility.
If the lift of the advanced cam is more or less the same as what is taken off of a shaved head or resurfaced block, you could always ask if a retiming was neccessary afterwards.

 

I've used soft solder through the spark plug hole to check valve to piston clearance on assembled engines. That was on hemi heads, might work on wedge heads, never tried.

 

Buy, or borrow a set of soft checking valve springs used for cam degreeing. Put #1 cylinder TDC compression and air up the cylinder. Nice to use a regulator, but you can get by without it. Leave air on the cylinder and swap out the valve springs for the checking springs. Check your clearance using dial indicator on the spring retainer. That gets you clearance info. As to performance, if you can't get info on the cam relative to the advance you should pull the timing cover and degree the cam while you have the check springs in place.

 

A stock engine with stock parts, camshaft, springs etc., you are very unlikely to ever run into any problems.

When you start replacing OG parts with performance components, hi lift cam &c., this is when you have to be really really careful, or stuff starts banging into each other and breaking. Coil bind.

The first thing to do is get it into your head that due to production tolerances and possible tolerance "stackups" there is no way to know where the cam will end up being "installed" regardless of where you think it should be. Lining up the dots or whatever doesn't mean anything. If you talk to engine builders who do this all day every day they point out finding cams as much as 15 or 18 degrees retarded, stuff like that. This is without taking into account defective grinds of the cam itself.

For what you're doing, your requirements, you don't need a Degree wheel, but you DO want to check and see where the valve closing event is with respect to TDC.

This is important because it is just as much labor to install it wrong as it is to take the time to do it right. Even a bare bones stock engine will benefit from careful cam installation and specified installed spring height. Don't cheap out, buy a set of new valve springs and shim them up to installed height.

When I did my Y Block, I didn't want to make a career out of it or purchase a Degree Wheel. There are "field expedient" methods to achieve the same thing. You can print out a wheel or use a pie plate, and make a pointer out of a coat hanger or whatever. With OHV engines except Nailheads, when the #1 cylinder valves are at TDC compression, the #6 valves are at overlap, and vice versa.

SO, you can remove the valve covers and rotate the engine by hand, when the valves are at TDC and/or split overlap, you can observe where the valve closing event occurs. It will show up on the pointer/damper a little before TDC, or a little after TDC. Make sense? Now you know, instead of guessing. Measure, don't guess! 4 to 8 degrees before TDC is what you want to see for your purposes. Again, it makes no difference what the dots say it "should" be, you need to check or you might be really unhappy.

 

Go here, https://www.blocklayer.com/degree-wheeleng.aspx insert your camshaft numbers to make a custom degree wheel. Then print it off any diameter you want, tape it to something solid and install and check your cam. The cam likely won't line up 100% due to manufacturing tolerances, but it better be close.

 

One thing I forgot to add. It might not be a factor for your application. Another thing that complicates the issue is when Federal smog regulations were enacted. One of the things the OEM did at that time was de-tune engines to decrease NOX emissions. Retarded or "late" valve timing was one way to achieve this. The effect generally is to reduce the effective compression.

Have to be careful with part #s, because a timing chain set might have the "smog" feature already baked in so to speak yet retain the original part #. Yet another reason why it pays to measure. In the case of my Y Block it was a matter of a worn timing set, which also results in late valve timing. Keep in mind please, you probably already know this, but valve timing is a completely different animal than ignition timing. Many engine builders also suggest installing camshaft in an advanced position to compensate for initial run-in chain stretch or wear. Once I got everything lined up correctly, static compression test went from a lazy 120-130 psi. cold to a nice snappy 150 across the board, it was very noticeable running the test. Manifold engine vacuum test was also improved.

Advancing the ignition timing is one way to try and compensate for late valve timing, but a key measurement to look at is whether the engine will pull the factory spec vacuum at factory ignition timing. Virtually all stock-ish engines should pull a steady 19" to 21" at sea level, or there is a major defect somewhere, and it will not run right and can't be made to run right until remedied.

 

Thanks for responses.
In this case I'm not going to replace springs and take heads off.
This is not a racing engine.
It has been over 30 years since I've done this.
I know I never checked valve clearance, I just didn't remember if I adjusted valves either.
I wasn't really wanting to know about degreeing a cam. Just trying to make a small change to my engine.
Assuming everything clears and the cam ends up in the perfect spot . All I wanted to know is will it work without tearing engine apart.

 

The reality is that you will not feel the change on a stock engine thru normal driving. Any change you do feel will be because you did something "HOT ROD" and are driving it harder. My car always runs better after I wash and wax it.

 

The rule of thumb is it takes about 4 deg. one way or another to notice. I'd agree with that. We're not talking major changes it's true, but for a stock street engine low end torque is what most people want. It places the power band where a lot of driving is done. If a cam ends up in a retarded or late position, plus the timing set is worn/stretched now we're now talking 8 degrees or even more. You will definitely notice an improvement in both measurement and seat of the pants. Cold weather starting will also improve. Good engine tuning isn't just one thing, it's a whole bunch of stuff that, taken together, starts to add up.

A lot of people confuse valve spring height or seat pressure and camshaft installation with "racing engines" only. I suppose it depends how picky you are, but you will never be disappointed by meeting factory specs. The valve train is really important on how an engine runs. Spring pressure might be "only" 90 pounds on a stocker, but you want to make sure it's 90 pounds, if that's what it is supposed to be.

 

Time for "THE CHART"..............

 

Fast, if this is the same hotrod you noted on another thread, it sounds like you already have a pretty
sweet ride with both ends covered w/ 4:10s and 23 mpg V8.

 

Thinking about 3.42 gears and advance cam 4 degrees. Trying for 26 to 28 mpg.

 

Funny how this video came up in youtube for me today, where they discuss this very thing:

 

Truck weight 2500 lbs. th200r4 trans. stock conv. 4.10 gears with 31 in tall tires. Engine is 355 9.5 compression. dual plane air gap intake manifold. alum heads. 2.02 valves. full roller rockers and roller cam. hei and fuel inj. cam specs are 284 int. / 310 exh duration . .470 intake and .480 exh. lift 110 lsa. It runs 175 degrees temp . afr is 15.5 . 2200 rpm at 70 mph. gets 23 mpg.

 

I do not know how to check valve clearance with the engine assembled. Someone else may have heard of a way or read about a way online.

Rotating the engine by hand sounds good on its face but you are still just guessing, things grow and stretch when an engine is running. A lot of the builders that I have known like to maintain .060 clearance (valve to piston) I have always made the assumption that this is why.

Most of the engines that we use are very forgiving and we can get away with a lot when we screw one together. Unlike a zero clearance type of e mill . You may get lucky. Ya just never know.

 

Too bad you can't just bump the C.R. by .5 to .7 from where you're at. I think you would get the increase in low end you're looking for.

 

Have you contacted the cam manufacture to find out if the grind includes the pattern being advanced?

A whole lot of cam grinders actually do build in advance. If you advance on top of that advance, you may be into part collision territory.

Checking for contact by rotating the engine by had just means that they did not hit. When the engine heats up, everything gets a little bigger.

Unless you have brutally stiff valve springs, at maximum velocity valves can travel past the end of the opening cycle by a little, before being "caught" and reversed by the spring. It is not much, but it is something.

Add up all of that expansion and what cleared cold and barely moving, and you might get a hit.

Get a hit and clay, gaskets, and the extra fuel that you are using now are gonna seem cheap.

 

At his current bore of 4.030" he would need to get 5-7cc's our of the chamber. That's assuming that the heads can take about a ~0.015-0.035" cut, or some combination of cut and thinner head gasket.

Of course that would mean taking it apart, which he does not want to do, to cut and then check the clearances.

 

As they show in the video I posted, they used a set of light valve springs, then they bring the piston up toward TDC compression and they open the valve until it contacts the piston using a dial indicator to measure valve travel. Do this with the crank in several positions and you find where the closest point of clearance is at, and how much clearance there is at that point. I believe they recommended .100" minimum clearance, if I understood them correctly. Changing the cam timing changes where that point is at the crank.

 

It's a mild cam. If it were a .600 lift I would be concerned.
Why would it matter if the cam had advance built in? lift is lift .
Just worried over clearance.