Advice? - cam gear issue and maybe badly out of sync

[CCCC]

The earlier thread ("Help with diagnosis?? ") outlined the breakdown. It ran fine onto and off trailers twice after I bought it and bit around the place, but it went down slowly (mile or two) as soon I got it up to speed on the highway.

Many good observations were posted, but suspecting timing chain slippage due to breakage of teeth on an original camshaft gear I uncovered that aspect. Although the PO said it had been replaced with a steel cam gear, the OEM fiber tooth gear is there, some teeth are broken, and the timing mark on the cam gear seems 180 degrees (well, maybe 179) off the TDC mark on the crankshaft gear - sure would have changed that gear beoroe running this truck if he had been truthful.

It looks like the cam gear is 180 degrees off because there is very good compression on #1 cyl coming up to TDC with the cam gear mark 180 off - BUT - am I coming up on exhaust stroke and getting comp because of bad valve action - or ??? There is no compression when both gear marks are coming up together, and did not seem to feel any suction on what would be the intake stroke before compression.

Have done all sorts of engine work on Chev/GM V8s but never on a 402 BB - so am wondering about possible cam/valve train damage. Does this engine have an interference fit - that is - will messed up cam timing cause bent push rods at least, and other possible problems beyond that? I could do a comp check on the other 7 cans to see if it is compressing in proper sequence, but hope to do something better.

Have you been here and determined the easiest/best way to insure sync? Is the only solution to undo the valve train, check/replace push rods as needed, and then sync the gears visually on #1 with everyting free? Or?

Questions ? Just ask. Thanks for any solid info and time/effort savers.

[geezer#99]

When you sync the gears on #1 where are the dots?

[budman k20]

Its hard to imagine that the engine would run if the cam was not timed correctly. A stock / mild built BBC is not an interference motor. If you rotate the crank 360 degrees more the timing marks will be aligned correctly (dot to dot) and the #1 piston will be at TDC once again.
Try this... Pull the #1 plug and have someone put their finger over the hole. Turn the motor over and when you start to get compression the marks should be on their way to alignment. You will have to stop when you have the dot to dot alignment on the crank and cam gear. Then confirm that the rotor is just about to align with the #1 spark plug wire contact in the cap. If all these conditions are met then the motor is timed close enough to run.
Good luck!

[geezer#99]

Rethink that budman!
Dot to dot is #6 tdc compression.
You need both dots at 12 oclock for #1 tdc.

[budman k20]

I guess I've been doing it wrong for 35 years then?

[geezer#99]

Not necessarilly!
You need to line them up like that to be accurate. Designed that way. But to get to #1 tdc you rotate the crank once.
Kinda hard if both are at 12 oclock

[budman k20]

You are correct! Both at 12 o'clock for #1 @ TDC and firing

[CCCC]

budman and geezer - thanks for this give and take. Very helpful. Glad to know that this stock 402 is not interference fit. There was quit a bit of slack/slop in the existing chain and that has me bothered.

I have done the comp test on #1 with a gauge and #1 is completing compression when the crank mark and the cam gear mark are both at about 12 o'clock. Yes, then rotated the crank 360 degrees and the marks are aligned adjacent at 12 and 6 o'clock and #1 seems to be topping its exhaust stroke.

Have always installed and aligned at 12 and 6 o'clock as shown in budman's diagram - but never thought about that being TDC for #6.

I need to calc that in my mind to assure it is synhronized and not off 180 degrees. Will run this through the old brain and check to see that #6 is at TDC compression when the marks are adjacent at 12 and 6 o'clock and also check dist rotor positions against all the above tomorrow afternoon - after it warms up a bit out there.

Once sync is certain I can find the cause of the no-run problem [probably dist/points/coil - maybe gunk in carb orifice(s)] and fix it.

Thanks again - please check back.

[special-K]

I'm watching for results. Something to learn here

[Possmguts]

I have never in my life heard someone say the the dots should both be at 12:00... the dots are supposed to be facing each other at TDC to be correct... If they are not then the timing is 180 degrees out.. a chevy motor can run on 180 out... but not very good... if those dots are lined up at TDC and the distributor rotor is pointing backwards then its 180 out....

[Shady Rascal]

A cam cannot be timed 180 degrees out. It's impossible.

The cam gear has exactly twice as many teeth as the crank gear. It's a 2:1 ratio. Every time the crank turns one revolution, the cam turns half a revolution. Remember, the cam only turns one time for every two engine revolutions.

You get it ? Time it crank dot up and cam dot down. Now turn engine one turn. What do you have now ? You have crank dot straight up and cam dot straight up. Now, turn it another full engine revolution. You will again have crank dot up and cam dot down.

Regardless of which is your preference, either way is right. When you go to drop distributor in, you turn engine until the crank TDC mark lines up and compression is coming out number one hole. That's number 1 compression and the point at which you drop distributor in with rotor pointing to number 1 terminal on the cap.

[CCCC]

Possm and Shady - I do not disagree in general. 180 out would be an impossible mess and I see no way that incidental chain slippage could yield that exactly.

For install accuracy the dots need to be adjacent (12 and 6 o'clock) - and Shady's revolution info is exactly what I have seen/described. Possm - a Chev V8 may run with the dist set 180 out (and not well), but would it run with cam/valve timing 180 out??

In my feeble brain it seems that the ?? remains. Which cyl is at top of compression when the dots are adjacent (crank 12 and cam 6 o'clock). Evidence seems to indicate it is not #1 - and #6 would be the logical alternative - eh? If the valve timing were so far off, I can't imagine having full compression on #1 right at the 12/12 clock positions.

Am going out there in a couple of hours to try another check or two, including dist rotor position. If all else is indeterminate, will pull every plug and do a sequential compression check. Good brain teaser here.

[geezer#99]

[QUOTE=CCCC;7528995

Which cyl is at top of compression when the dots are adjacent (crank 12 and cam 6 o'clock). .[/QUOTE]

It's #6 !!

And fwiw your's or any motor won't run at 180 degrees out.

[Possmguts]

Well, I'm not trying to be rude by any means when I say this, but with conflicting suggestions you are getting here and the confusion its causing... I would simply google what you have and how to set crank to cam timing along with distributor timing...

But to answer your question to me.. no I'm sure it would not start with cam and crank gears not lined up at the dots. I'm pretty sure you would have heard lots of nasty sounds and then nothing... and that would have been bad...

The fact that you said it ran tells me the gear timing was set. But if you do have lots of chain slop, I would not hesitate to put a new gear and chain set in it.

I honestly think you have a different issue here... fuel, vacuum, carb, bad distributor, no compression...?

[geezer#99]

If you doubt my info then google it and a hundred links come up with the same info.
Just like this.
http://www.camaros.net/forums/18-eng...350-chevy.html

[CCCC]

Possm you are definitely not being rude - have been helpful - and geezer, you have been good with this issue and I haven't disagreed with your view at all. Your cited thread was very helpful - shows the confusion out there.

I merely need to convince myself because, even after installing many crank/cam gears with chain and never having any timing problems afterward - I had never before dug into the matter of which cyl is at top of compression stroke when those marks are adjacent (12 and 6 o'clock). If I had not explored and found #1 cyl up on compression when the gear marks are at 12 and 12, probably never would have gotten this itch.

As it stands, I am glad to read that #1 is up on compression when the marks are at 12 and 12 (#6 on compression when marks are adjacent at 12/6) because that will dispel the thought about cam/valve timing problems. Once done with further check/analysis on my BB402 out there, I will post here any further info.

Thanks gentlemen

[CCCC]

OK - CHECKED IT OUT again to the best of my ability.
Crank gear, cam gear and distributor rotor are in synch on this engine.

#1 cyl is at TDC compression when both gear marks are at 12 o'clock.
#6 cyl is at TDC compression when the gear marks are adjacent - that is - crank gear at 12 oclock abd cam gear at 6 0,clock - as they should be when installing new gears and chain.

I'm going to the bank with this as correct. Once I get these new gears/chain on, pan installed and all pieces of the front assembly back together, I will get this thing running with either some carb work/cleanout or/and some correction of dist/points, etc. Unless the coil quit - and that one should be easy.

Thanks to geezer, possm, shady and all who chimed in.

[67 chevelle]

It is correct CCCC , 12 oclock for both dots for number one fire , dot to dot is fire for number six , and you guys wondered why you always had the distributor out 180 on initial fire up after a chain swap or rebuild

[TeamEstep]

Originally Posted by 67 chevelle

It is correct CCCC , 12 oclock for both dots for number one fire , dot to dot is fire for number six , and you guys wondered why you always had the distributor out 180 on initial fire up after a chain swap or rebuild

That totally makes sense now!

I've got one better. When I was a high school kid, I had a '70 el Camino and had rebuilt the 350. I had started to tap on the main timing gear on to the crank and realized part way, that I had it on backward. No problem I thought, I'll just look to see where the mark is behind the gear and line it up with the cam gear. After many attempts to get it started, I discovered that the woodruf key is offset from the dot and my timing was around 60 degrees off. I'm 54 now and I've learned a lot since then.

[special-K]

Does it really matter what time of day you line this stuff up? AM? PM?

Once you can crank, try cranking some straight Sea Foam into the carb and let it sit. Then crank it through later. That has kept me from going inside a carb before

[CCCC]

Hey, special-K - that stuff lines up best at about 3:58 AM. Some guys still don't believe the #6-up-on-compression thing. None of the gals believe it - or care

Thanks for the thought on cranking the straight Sea Foam into the carb and letting it soak in. Since this shutdown first and only time came on after running well for 10 - 15 minutes, you may have the ticket there. I'll let you know what happens.

[Ironangel]

Originally Posted by special-K

Does it really matter what time of day you line this stuff up? AM? PM?

Once you can crank, try cranking some straight Sea Foam into the carb and let it sit. Then crank it through later. That has kept me from going inside a carb before

Of course it matters! 12-oclock is always 12 o-clock twice daily...As long the motor is oriented with true north, magnetic north is the timing mark. "SeaFoam"...Good stuff, tastes great on pancakes!

[special-K]

Yeah, 4-strokes do very little for most women

Originally Posted by Ironangel

Of course it matters! 12-oclock is always 12 o-clock twice daily...As long the motor is oriented with true north, magnetic north is the timing mark. "SeaFoam"...Good stuff, tastes great on pancakes!

Would this hold true for our fellow members Down Under? I need to warn everyone in case you run out of Sea Foam like I did. DO NOT USE SUBSTITUTES!! I ran out, so I tried using the real thing straight off the beach. I don't know if I got sand in there or maybe it was the salt, but it clarly was not a good idea. I wish someone could have warned me!!

[geezer#99]

Well at least you guys don't need to convert to metric time when you install your gears!!
It's a real pain needing to use #8 and #5 cylinders to line it all up.
And then daylight saving time and the ever changing exchange rate confuse it more!
And I thought sea soil was a substitute for sea foam.
High test compared with your low octane swill!
You gotta try some of that high test!
Makes your hair grow back!!
Or on the front--
Or the sides------
Or........

[CCCC]

Originally Posted by special-K

Yeah, 4-strokes do very little for most women
Would this hold true for our fellow members Down Under? I need to warn everyone in case you run out of Sea Foam like I did. DO NOT USE SUBSTITUTES!! I ran out, so I tried using the real thing straight off the beach. I don't know if I got sand in there or maybe it was the salt, but it clarly was not a good idea. I wish someone could have warned me!!

Well, having been to Australia a few times and having wandered around NZ for three weeks - and on the beaches in both places as well as in Fiji - I can tell you that the SEA FOAM in the southern hemisphere definitely is different than the stuff we get up here. I can't make a guess about how it works, but the counter-clockwise downflow might affect it as well Just dunno.

And, if timing a Chev/GM V8 over there, the whole timing setup is probably altered because their time is so different on the other side of the dateline. Glad I'm not trying to do this stuff over there.