Cam Timing is Off

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Rick
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Cam Timing is Off

Post by Rick » Wed Feb 12, 2014 4:18 pm

I posted my troubles on the Samba but I figured this would be a good "first" post here. Here's the deal. I'm in the process of rebuilding the 2.0L from my '77 bus. I'm using my old "bolt-on" cam gear on a new Web Cam stock grind solid lifter cam with their lifters.

I assembled the case, timed the cam and crank just like it says in the books, installed the pistons, cylinders, heads, valve train and adjusted #1 valves when the piston was at TDC(compression stroke). I adjusted the valves to .006", but when I rotated the crank 180 degrees to adjust the valves on #4, I noticed the lash on #1 intake would increase to .012". The lash on the exhaust valve would increase too when I rotated the crank further through the cycle.


I came to the conclusion my cam timing was about 67 degrees too far advanced, so I split the case expecting to find my crank/cam dots not lined up. Nope. They were lined up just like they were supposed to be.

It just so happens the bolt hole centers on the cam gear are about 67 degrees apart, but there's only one way that all five holes line up with the holes in the cam. I checked the gear on both the old and the new cam and noted what positions the cam lobes were in. Both were the same. This engine ran good with this cam gear so I know the gear isn't funky, unless the guy that rebuilt this engine last, knew something about it that I don't.

Did I check the cam timing right? This is how I did it. I put a dial indicator on #1 intake lifter and rotated the crank. According to my spec sheet on this cam, the intake opens at 3 degrees BTDC. On mine, the lifter started to rise at about 75 degrees BTDC. The spec sheet says the intake closes at 33 degrees ABDC. Mine closed at 34 degrees BBDC.

Am I doing this wrong? If not, any ideas why my timing marks line up when the timing is way off?

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Amskeptic
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Re: Cam Timing is Off

Post by Amskeptic » Wed Feb 12, 2014 7:39 pm

Rick wrote: I adjusted the valves to .006", but when I rotated the crank 180 degrees to adjust the valves on #4, I noticed the lash on #1 intake would increase to .012".
Is this the only criterium by which you are basing your speculation that the cam/crank timing is off?

Cuz . . . the camshaft does move inside its bearings the case when it is loaded on different sides, which allows the clearance at the stem/rocker to either open up or close a little. Also, at TDC, the followers are not on the absolute bottom of the lobe base circle.

Rule to live by: adjust at TDC and DO NOT worry about variations in clearance for that valve from there.

Recheck your degree chart, and if the valve follows the chart, consider your valve timing acceptable.
Colin
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
Pluck - 1973 Squareback . . . . . . 55,600 miles
Alexus - 91 Lexus LS400 . . . 96,675 miles

Rick
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Re: Cam Timing is Off

Post by Rick » Wed Feb 12, 2014 10:11 pm

I'm thinking my timing was off based on this: According to my spec sheet on this cam, the intake opens at 3 degrees BTDC. On mine, the lifter started to rise at about 75 degrees BTDC. The spec sheet says the intake closes at 33 degrees ABDC. Mine closed at 34 degrees BBDC.

As long as I'm doing the measuring correctly and interpreting the info on the spec sheet correctly, I think the cam timing was about 70 degrees too far advanced, and it just so happens the bolt centers on the gear are about 70 degrees apart. I'm wondering if this cam gear was drilled wrong.

I did discover that the gear lash was way off in certain spots on the gear. It went from zero lash(this must have been the spot that I checked) to .011" on one particular spot on the gear.

The average lash came to about .005" and the gear is marked with a "N3". Which gear pitch should I get to correct this? Thanks for the reply.

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Re: Cam Timing is Off

Post by Amskeptic » Thu Feb 13, 2014 10:06 am

Rick wrote:I'm thinking my timing was off based on this: According to my spec sheet on this cam, the intake opens at 3 degrees BTDC. On mine, the lifter started to rise at about 75 degrees BTDC. The spec sheet says the intake closes at 33 degrees ABDC. Mine closed at 34 degrees BBDC.
Spec : 3 btdc to 33 abdc for a duration of 216*
Actual: 75 btdc to 34 bbdc for a duration of 221*
Does this suggest that you have some performance long duration cam incorrectly sent/installed?
Rick wrote: As long as I'm doing the measuring correctly and interpreting the info on the spec sheet correctly, I think the cam timing was about 70 degrees too far advanced, and it just so happens the bolt centers on the gear are about 70 degrees apart. I'm wondering if this cam gear was drilled wrong.
see above + yes, everything is seriously screwed up.

You know that the easiest most visible confirmation of correctly set up cam/crank is to have the #1 crank throw at TDC and just check to see that the cam lobes are at overlap for #3 position, i.e. you see a "vee" between the intake/exhaust lobes as they point directly towards where the lifter bores would be.
Rick wrote: I did discover that the gear lash was way off in certain spots on the gear. It went from zero lash(this must have been the spot that I checked) to .011" on one particular spot on the gear.

The average lash came to about .005" and the gear is marked with a "N3". Which gear pitch should I get to correct this? Thanks for the reply.
This is an ABORT, do not continue.

I swear (!), do not allow these trash merchants to make your life miserable with this crap. You do NOT average your cam lash, there should be NO cam gear run-out and do not allow those morons to tell you otherwise! There is no gear number to suggest until you find one that runs true so you can then see which number will yield "no play/no walk".
ColinNowI'mCranky
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
Pluck - 1973 Squareback . . . . . . 55,600 miles
Alexus - 91 Lexus LS400 . . . 96,675 miles

Rick
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Re: Cam Timing is Off

Post by Rick » Thu Feb 13, 2014 10:56 am

Hey Colin,

Thanks for taking the time to respond and sorry I didn't mean to pee in your cornflakes. : )

I'm not going any further until I find another gear. I'm in the process of that right now. The cam is marked "STK" for stock grind. I guess they could have stamped it wrong. The engine was running with this gear when I bought the bus, but if I remember right there was a slight popping sound coming out of the carburetors. This would happen if the cam timing was off, right?

Hopefully this mystery will be solved once I get a new gear. I will report back.

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Amskeptic
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Re: Cam Timing is Off

Post by Amskeptic » Thu Feb 13, 2014 1:22 pm

Rick wrote:Hey Colin,

Thanks for taking the time to respond and sorry I didn't mean to pee in your cornflakes. : )
You did not pee in my cornflakes (p.s. eww gross), they did. We are of one tribe here. You may or may not remember that these cars were sold new off the showroom floor with unexpectedly high quality. I have been loyal to these cars ever since. I suffer a thousand cuts a day as I watch the new contemptible junk we must use destroy the joy these cars used to provide with their legendary reliability (a phrase rendered useless in today's advertising universe). Allow me to rant a little . . .
Rick wrote: I'm not going any further until I find another gear. I'm in the process of that right now. The cam is marked "STK" for stock grind. I guess they could have stamped it wrong. The engine was running with this gear when I bought the bus, but if I remember right there was a slight popping sound coming out of the carburetors. This would happen if the cam timing was off, right?

Hopefully this mystery will be solved once I get a new gear. I will report back.
Cam timing or generous overlap which also diminishes the vacuum signal at idle. Please research your actual cam's behavior. If you use stock induction (carburetion or FI, you really need to make sure you have stock duration/overlap. I have discovered an epidemic of "performance camshafts" that take away the low end torque that makes these cars tractable and steady, in favor of "better performance" that we rarely use because it only "comes on cam" where most of us refuse to push in the rpm band.

Please demand and require of yourself and others that the gear runs perfectly true.
Colin
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
Pluck - 1973 Squareback . . . . . . 55,600 miles
Alexus - 91 Lexus LS400 . . . 96,675 miles

Rick
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Re: Cam Timing is Off

Post by Rick » Thu Feb 13, 2014 3:24 pm

I just got off the phone with Web Cam and they explained to me how to check the valve timing. When they say the intake opens at 3 degrees BTDC, that's with zero valve lash and at .050" inches of valve lift and measured at the valve spring retainer. I was measuring right on the lifter(I had to put two lifters in the same bore so that my dial indicator would reach). Does it matter if I'm not measuring at the valve retainer? Are the rockers a 1:1 ratio. I was hoping to measure right off the cam while I have the case split.

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Amskeptic
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Re: Cam Timing is Off

Post by Amskeptic » Fri Feb 14, 2014 8:21 pm

Rick wrote:I just got off the phone with Web Cam and they explained to me how to check the valve timing. When they say the intake opens at 3 degrees BTDC, that's with zero valve lash and at .050" inches of valve lift and measured at the valve spring retainer. I was measuring right on the lifter(I had to put two lifters in the same bore so that my dial indicator would reach). Does it matter if I'm not measuring at the valve retainer? Are the rockers a 1:1 ratio. I was hoping to measure right off the cam while I have the case split.
Stock rockers are 1:1. You should be able to do duration/lift off the cam, but if it wiggles out of the bearing, all numbers are too easily kablooey.
Colin
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
Pluck - 1973 Squareback . . . . . . 55,600 miles
Alexus - 91 Lexus LS400 . . . 96,675 miles

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