Cam timing in the car? Possible?

[VFR750]

Can you adjust cam timing in the car? Do you have enough room with the muffler and tin removed to get the wrenches on and torque the bolt?

After a less than statisfying first start, I has diagnosed the RHS cam is off.

Not my best day.

911sc, 3.0l.

[Flat6pac]

I've done it before, truly not worth the extra effort. Engine still needs to be lowered.
Bruce

[boyt911sc]

Originally Posted by VFR750

Can you adjust cam timing in the car? Do you have enough room with the muffler and tin removed to get the wrenches on and torque the bolt?

After a less than statisfying first start, I has diagnosed the RHS cam is off.

Not my best day.

911sc, 3.0l.

VFR750,

How did you diagnose that the right side cam was off in timing? You could do a partial engine drop to gain access to the cam/s and it would be very awkward doing this job that requires precision measurements. What is preventing you from doing a full engine drop and do the cam timing with the engine on a bench or engine stand? What you are thinking is doable and could be done easily by people with skill and experience.

If you made a mistake doing the cam timing with the engine sitting on an engine stand do you think you could do better with the engine installed? I've performed more than a dozen cam timing settings and would not even consider doing one with the engine in situ. This is a decision that you have to choose.

Tony

[VFR750]

Engine almost out....

I timed the LHS perfectly. And it is still in spec.

The RHS is off again. I verified in the car. There is enough room to do it.

It is supposed to be set at 2.4mm. And it came out at <1mm. About 30 degrees retarded. Very odd. I am way off on the RHS.

But this is the second time I've found the RHS out and the LHS in spec.

Something is going on. Is it possible to jump timing if the hydraulic tensioner poops out? Would it jump to a retarded position? That wouldn't explains first error. But I was really paying attention the second time.

I'm using the stomski mechanical adjusted to set the timing. So I should have no issue with tensioning the chain.

Carrera tensioners installed.

[Flat6pac]

Thought process isn't right. If you jumped a cog you would be off way more than 1,4.
Bruce

[SoyRacer]

Its possible . . . just awkward. I actually have a fixture from over fifteen years ago that takes the place of the engine mount to allow open access to chain housings and crank pulley. (Been at this for a while)

[VFR750]

Based on the angular difference between the left and right is that enough to be off a tooth?

[VFR750]

What I mean is, the angle of rotation on the crankshaft to reach 2.4mm lift difference between the LHS (good) and the RHS (retarded) is around 30 -40 degrees.

That feels like a sprocket tooth difference.

[VFR750]

Added info.

I heard some rattling for a brief moment. Since I have a loose baffle in the muffler I thought that was it.

Now I wonder, could that be a bad tensioner, sagging when shut off, and then repressurizing on start up?

[VFR750]

Originally Posted by Flat6pac

Thought process isn't right. If you jumped a cog you would be off way more than 1,4.
Bruce

It takes about 30-40 degrees rotation to go from just touching the ramp to get to 2.4mm on the LHS.

I will try to check and get better numbers to verify if the difference can be explained by a tooth jump.

Thanks for the push back. What it means to me is you are pushing me to think about it more. Which is ok. It challenges me to be very specific about what the difference is. Left to right. Is it exactly one tooth off?

[VFR750]

Just looked at a picture of the cam gear. Looks to be 36-40 teeth. Jumping One tooth would be 16-20 degrees in crankshaft position relative to the timing.

So I've confirmed, jumping 1-2 teeth could explain the problem.

Carrera pressure fed tensioner

[Walt Fricke]

Well, I'd look at something else. One simply does not hear of chains jumping teeth. If a tensioner lets go, you get a horrible rattle, exacerbated some by engine speed. People drive home knowing their tensioner is shot. Of course, they pussy foot it.

Bruce says one tooth is more than the 1.4mm change you show. He's got a lot of experience. And I don't think the chain can jump a tooth on the sprocket on the cam, which is the big one. If it jumps, it would be on the smaller gear on the intermediate shaft, and that is going to have a lot more influence on timing. Remember, there is a gear on the crank which turns the IS shaft at a lower rate. Then the chain gearing turns it lower still, though the combined effect is 2 to one (the reason for this sort of offset gearing is to be sure the gears and chains wear evenly).

And it only takes a tiny cam change to move the valve 1.4mm or less where you measure it.

Tensioners don't sag. The tension is created by the spring inside. The oil just acts like a shock absorber, dampening the harmonics otherwise present. So you have the same tension at all times, it just doesn't work well if the oil pressure part fails. And it isn't the pressure of the oil coming in which matters - the purpose of the feeding is to be sure that the oil chamber is full at all times so it can do its shock absorbing task. Fact is, solid tensioners work fine on race motors if set carefully. It is just that they have to be checked often, and aren't right for the extremes of day to day driving.

Which type of cam do you have? The earlier big nut kind? Or the later, harder to adjust, bolt kind?

Why don't you take some pictures of your cam timing setup and post them?

[VFR750]

First, I said <1, and that 2.4mm came 30-40 degrees ATDC. That is of the same magnitude as a couple of cam sprocket teeth or 1 intermediate shaft tooth.

What you said makes sense that the smaller sprocket could have jumped if a loose chain overshot the sprocket.

Also, I did hear a horrible rattle, but I assumes that was the loose baffle in the muffler. But I had never heard it before and it went away after a short while. I did not time how long. In retrospect, it was abnormal and I should have stopped right there.

I cam show you how I timed the cam, but it will look like the LHS. Dial gage, extension shaft, Z-block. Resting on the outer flat of the retainers. RHS just like LHS. LHS has not changed. Later style with bolt and pin.

Cams are a custom DRC dc20/19 with 110 lobe centers, combined with DRC springs. So the forces on tbe chain are a lot higher than stock.

Other things to consider, before I tore down the engine I had a ticking sound, later confirmed to be a loose cam gear on the crankshaft. Also the RHS idler arm bushing were worn way over spec. Both were fixed/replaced. I kept RHS tensioner on the RHS always.

Part of the reason I pulled the engine last year was it was running poorly and oddly loud. I also found a blown head gasket on #2. Had previously ran at Thompson Moter speedway road course.

The sounds I heard on the test drive sounded similar to before the rebuild.

Related?

Don't know.

But all data that needs to be considered.

At least the oil came out pretty clean and nothing on the magnetic drain plugs.

[DSPTurtle]

The left hand side chain is more difficult to make sure for proper engagement on the IMS gear but... That doesn't mean it can't happen. It's possible your right side chain was not over both teeth. Happens a lot when setting up timing chains on aflas. Did you notice if the chain was "tighter" on the RHS? It's possible that it wasn't fully engaged and once you start it, it found the happy place and shifted the timing by a tooth. Low probability but that why I roll the motor over a dozen or so times before I start making final adjustments. Either way, you'll get it sorted!

[VFR750]

As part of the timing process, you rotate the crankshaft several times and verify the timing repeats. Which I did, and it did.

Any chain anomaly during the first setting would disappear when you rotate the crank through several cycles past TDC.

But it is something to be conscious of

[Flat6pac]

If you screwed up the cam timing too much and ran it, you'll be into bent valves contacting the Pistons especially on the exhaust side.
I suggest you pull the engine, put it on the table and find out what the problems are. Everything should turn smoothly and be in sync.
Chains don't just jump, cams don't get off spec by them selves, and strange noises aren't part of the rebuild. You're trying to work upside down and resolve the problems, pull the engine and save your self time and agrivation
Bruce

[VFR750]

Engines out and the teardown has started.

Yes I ran it, and it was not smooth. So, yes I have already screwed up. Inexperience does that occasionally.

I have JE pistons, so hopefully the deeper pockets help in avoiding valve contact for the magnitude of the timing difference.

The 110 lobe center is much less aggressive than the 98 used on some cams. And the duration is similar to the 964 cam. My fingers are crossed that this was a mild enough cam to avoid piston contact.

[VFR750]

Originally Posted by Walt Fricke

Why don't you take some pictures of your cam timing setup and post them?

Here is my setup: I'm setting up to check timing now.


10mm range Dial indicator on the large flat on the retainer. Set at 9.0 mm deflected, looking for 6.6mm for 2.4mm lift. Valve clearance set to 0.1mm (0.004")

This is what it looked like when I did it:

[Flat6pac]

What is the cam spec for setting valve movement on 360 degree rotation of crank. I don't understand the concern of 6,6.
If 2.4 is your spec, valve lash is .1 mm, that's the only numbers you should be concerned with. The 9.0 and the 6.6 is useless information.
Bruce

[VFR750]

You start at TDC (valves closed) Z1

Set the dial gage at some value. Whatever you choose, you have to compress (deflect) the dial gage such that you can measure the motion of the valve. In my case I precompressed the dial gage 9mm.

Rotate the crankshaft 360 degrees back to TDC.

At that point there should be 2.4mm of lift.

9.0mm - 2.4 = 6.6mm on the dial gage.

That is how it is done.

My problem is my RHS is now requiring 30-40 degrees past TDC to deflect the valve 2.4mm. Which is bad.

The 9mm I refer to is just my starting point. You can do any value you want, provided the dial gage has enough range to deflect 2.4mm ( for my particular cam)