Timing jumped?
 

Here are the symptoms:

1) engine a bit harder to crank (like way to advanced)
2) almost immediately backfires pushing fuel all over the place (thank god for flame arrestors)
3) IF engine starts, at low rpm sounds like a miss
4) at 2000+ just sounds rough w/miss
5) when turned off hear a sound almost like a pressure release


.......Is it possible its just the timing chain jumped and i'm getting the compression stroke pushing back up into the intake? Reason is, sounds similar to when i've been through this on autos...etc.

Whats the general vote on this? :rolleyes:

Another possibility is a flat cam lobe. If so probably the exhaust. Just a guess though.

Ron

More likely than the timing chain jump is a distributor gear thats worn out or has broken teeth.

Guys.........thanks for the reply. Its the old, engine ran great before putting it to sleep last year, but heck, now, when that backfire happens (almost immediately), I am talking lots of fuel being pushed back.

I will pull the distributor 1st. The piece about, when I turn it off, a pressure release you can hear........very strange.


Thanks........Bob:cool:

kcat
you may want to pull the cap and rotor and look at the springs. it's possible one or both broke off and is advancing too early.

Checked the wires and order again (just because I did new stuff on both engines 1st thing this year), orders were ok.

Next:
1) Check points/springs...etc
2) Gonna watch the rotor rotation on start for continuity
3) Mark dist @ #1 on cap, then cranking engine to see if harmonic mark is same as when #1 on dist is there.
4) Pull distributor to check gear.

.....any other ideas.


Bob

To check for a flat cam lobe you can cut the oil filter open and see if there is any silver metalic residue. Right after running the silver film should be on the dipstick also.

The thing that makes me think it is a cam lobe is the leaking down sound you are hearing and the back firing. If the exhaust valve wont open the engine will exhaust the combustion gases through the intake valve when it opens causing a backfire and spitting out any air fuel mixture in the manifold. Or with an exhaust valve stuck closed the burned gas cant escape and is recompressed and may make a leak down sound when shut down.

Maybe a broken valve spring also.

Just guesses again. I hope its just an ignition problem.

Ron

Sounds like a chain or a gear. I think Griff hit it . Points?

Thanks again..........I've got it all on a checklist for Saturday.

so what was the outcome of the checks??

I'd like to know if you have tried to make it run right by rotating the distributor and timing it by ear. I may be a simplton, but I have inadvertently bumped the advance knob on my fancy timing light more than once (before setting timing) and been alarmed at the result, before relizing what happened. I was ready to tear the motor down one time before the "your a dumb ass" light came on.

BT :cool:

make sure no mouse house in the exhaust, pesky critters!could be in far enough to hold a exhaust valve open. I always had to plug my flat bottom every year with plumbers test plugs. Just a thought Paul

Ok here is the latest. (And Jaf302, long time ago had something similar on a car, the cat converter broke apart hosing up the exhaust)......but back to my story.

Today pulled off the timing cover and all. With the marks inwards, (and they are aligned perfectly, no slack at all) the harmonic IS AT TDC 0*. BUT, the distributor is at about #6. So, does this just sound like the gear has just twisted on the distributor shaft. (pin broke or something like that).

Right?.........Imbarrased to confirm this but. With both marks facing inwards and the HB at TDC, I should be firing #1 (correct)?

with the marks aligned I think #6 is fireing and #1 is in overlap If the valve cover is off rock the crank back and forth with a breaker bar and #1 valves should move. the exhaust when you turn clockwise and the intake counter clockwise

If you stab the distributor and put it on the number one cylinder with both timing marks aligned inward as close as they can get together you will be 180 degrees out.

Dont ask how I know this.

Rotate the engine 360 degrees from where it is now and you should be on # 1 cylinder. Both timing marks will be at the top of their gears. If it lines up on number one you havent jumped timing.

Good luck,

Ron

Guess I should have confirmed this first. Its a 1986 BBC. (the typical high perf GM that KAAMA used).

What are the positions for the timing marks? (cam/top crank/top, cam/down crank up)..? :rolleyes: My older auto manuals had them as closest which would have been cam/down and crank/up).


Bob

With the BBC the dots should be aligned between the center of both gears.( next to each other ) With the harmonic balancer at 0 degrees the two marks should line up and the rotor in the distributer should be pointing directly at #1 wire post. Was the dist. loose? Is there any chance it got turned? If no to both of these questions than pull the dist. and check the gear for badly worn or missing teeth. GOOD LUCK

Tinkerboater. Going to re-check the distributor this morning. But, as the engine sits now, it is exactly as you had said. Camshaft is down, Crank is up making them closest to each other, Balancer (if I just place it on) is at TDC, but the distributor is at #6.

.........thanks for all the help.........(so far:cool: )

Be careful. I believe your timing is correct with the distributor pointing at # 6 with the marks aligned. I timed an engine like Tinker says and it was 180 off. To be sure you need to rotate the crank 360 degrees untill both timing marks are at the top of the gears to get the distributor to point to number one.

Think about it. If what Tinker says is correct your engine is 180 degrees off on distributor timing. I doubt your engine is 180 degrees off like it sits now because you said it will run somewhat. At 180 degrees off it will do nothing but backfire ocasionally while cranking.

Ron

If the roll pin on the dist gear let go, it wouldn't run and you wouldn't get oil pressure. Stupid question... but did you make sure the rotor isn't broke and spinning on the dist. shaft? Also make sure it is clean. A greasy hand spinning the rotor around to get the dist to drop will result in your symtoms.
If it isn't the rotor, and the dist gear checks out ok, I would try re-timing the engine and firing it up to see what you get.
From my memory, when the marks on the gears are aligned you are at tdc on the #1 cylinder, starting the power stroke.

BT :cool:

Will find out tomorrow. Wanted to pull the plugs today so I didnt stress the starter. (and that in-itself is a project). I also want to watch the total valve train when the engine is moving.

After thinking about it again. The balancer would only reach the 0* mark two times overall. Once for #1 and the other for #6. If I am aligned with both marks inward (cam @ 0600 and crank @ 1200) #1 would be on the compression stroke and ready to fire. The next time the crank its turned 360*, #6 would be at the compression stroke and ready to fire, but I would expect the cam gear mark to be @ 12:00 and the crank @r 12:00.

My distributor is @ #6ish.

I hope I get a good laugh out of this when its over. Its almost comical. (unless i'm still at it a month from now).

YOU GUYS NEED TO READ THE BOOK -- I stand by my earlier post. I have two engines running just fine with the set up I said.

There, you just figured it out for yourself. The engine appears to be timed correctly. I have built several engines and on the first few I installed the cam with both marks closest together then stabbed the distributor aligned to # 1. It never failed the timing was 180 degrees off. Solved the problem by rewiring the distributor once. Restabbed a couple of other times. Finally I would check for compression. Thats when I realised what was happening. Since then I still install the cam with the marks aligned closest together but then rotate the crank 360 degrees to get #1 on the compression stroke. When this is done the marks are both at 12 o'clock. Never have any timing issues anymore.

Another clue that the timing is not 180 degrees out is the fact that the engine runs at all. I can tell you from experience that at 180 degrees out the engine will not run at all.

I hate to say it but if you have ruled out any electronic or mechanical timing advance malfunction I would look at the cam lobes and lifters. I had a 454 that did the same thing once and it was a cam lobe. This was a high milage engine in a Chevelle.

Good luck and keep us posted.

Ron

Tinker,

Just checked the Mercruiser service manual. It says to install the cam with the marks closest together. It makes no mention that this should give you #1 cylinder at TDC compression stroke. In another section about installing the distributor it makes no mention of where the timing marks on the gears should be. It just says to check for #1 to be at TDC and on compression stroke by rocking the rockers to be sure that both valves are closed and the lifter is on the base circle.

GM designed this so it would be easier to install the cam without being one tooth off. But this is about valve timing not ignition timing.

If your theory is correct then Kamma's engine has jumped time by 180 degrees. He has already stated that the engine runs somewhat and even claims to just have a mis at 2000 rpm. This would hardly be possible with an engine miss timed by 180 degrees.

Respectfully,

Ron

Dare I jump into the fray ??

Put your finger in the #1 plug hole and crank over the engine. When it pushes your finder out the #1 piston is on compression going up to TDC. Continue turning slightly until balancer is at TDC and the crank is on the "correct" revolution for compression/firing.

At this time the BBC timing marks should be directly across from each other at their closest point of approach, give or take 2-4 degrees in case your cam wasn't installed "straight up".

Align the distributor rotor a few degrees CCW of the #1 plug wire, to account for the fact that the rotor will turn a little when you slip in in from the "twist" in the gear, and drop it intp place.

It should actually start at 0 degrees advance (as long as it's out of gear so there is no load) and then allow you to set timing. If not you can twist the distributor "around" 10 degrees in the opposite direction of the rotor rotation and then lock it down.

Now to the miss. Also check that all the valves are actually moving as it cranks over. I've wiped off a cam lobe before, and the motor would run but had a very difficult to trace miss in it.

Good Luck - Greg


I guess I'll add that the BBC will actually run with about 15-20 degrees of timing error, as when I broke my crank in two it still ran, without any miss, even though I could turn the front two cylinders about 20 degrees before the back two would start to move.

kcat,
after your engine is running again by the method which greg p. explained, and you set your timing with a light ; if you still have a miss, you can pull one wire at a time from the distributor cap while running and missing and when you find the culprit, it will stop missing if its a stuck valve, bad valve, worn lobe.(unless there is more than one)
just to add to the turmoil, some cams are ground with advance in them, the comp cams i use have 4*ground in them even when they are dot to dot.
down where your springs are under the rotor there are stop posts that limit the mechanical advance in some distibutors. i've seen them break off and over advance.
one last bit of trivia, i know of a small block that ran 180* out for a few minutes. then the air cleaner blew off from a backfire and hit my friend in the head causing him to get stiches.

Thanks. I may get up to it tonight, and watch the valve train and the distributor while cranking.

This (again) is almost stupid. Im thinking how many times I've rebuilt a motor, and you just do this stuff without looking, put in the distributor....and sha-zam, "ITS ALIVE"..........then one day comes and you forget your name.

But would you guys agree (and not even checking for compression strike with plug removed, or watching the valves). If the marks are inwards at 6pm/12am, AND the balancer is facing TDC, the engine "can" ONLY be at the #1 position, and the distibutor "should" also be in #1-land.

Bob "My-Brain-Hurts" KAAMACAT :)

You can install the distributer in any position that you want. All that matters is that the rotor is pointed at the post that you intend to use as #1 plug wire. With the cam marks both pointed up you will have to point the rotor at #6 because that will be the first one to fire in your rotation order. You made #6 into #1.

Yes... I agree with that. 6 oclock on both dots will give you 180 degrees off number 1 firing. 6 oclock and 12 oclock will give you TDC on number 1, starting power stroke. Did you clean the greasy hand print off the rotor yet? :D

BT :cool:

Let us know how it comes out. I am interested to know. I will stand by my statements.

For the record I believe that your engine is timed correctly as it sits now if you have not changed anything. That is being with timing marks aligned at the 6 oclock (cam) and 12 oclock (crank) and the distributor pointing at # 6 wire post. If you were to rotate the crank 360 degrees the timing marks will both be at 12 oclock and the distributor will be at the #1 wire post. I believe this to be correct timing on a BBC.

I have been wrong before but I just went through this last January.

Good luck and post what you find.

Ron

Tinker is right on.

Hey Kaamacat!

Whats been going on with your engine. Had a chance to look at it again?

Inquiring minds want to know.

Ron

How does thay saying go "It takes a big moron to admit their mistakes...." or something like that.

Well, after checking the wires, pulling the timing cover, checking the movement of every valvetrain component, taking the distributor apart (totally)........here we go.

I put it all back together, sounds a bit better but right when you drop to 1500 it starts to "cough/sneeze". (honestly). Got mad thinking this ain't right, its something simple. Went to check it again Saturday.................

.....followed each plug wire up to the left side loom, 1-3-5-7. Then checked the order on the cap. 1;) 3;) 5:eek: 7:mad: ......All this and I guess i'm just blind or need to take my glasses to the boat.

5 and 7 were switched on the cap.

Here is the best part. I switch 5 and 7 back to "normal", just touch the key and literally cant stop the motor from starting. GREAT NEWS........NOW GET THIS.......I crank the enging just a few times so I can repaint the tdc on the balancer (and remember I said that NOW the damn thing starts almost by looking at it). Later in the day I go to adjust the timing and hear a nasty noise, from all of the problems the damn starter gear split. So guess Im off to the rebuild shop today.

So, what, 1month later, broken tools (and some new ones), countless bruises and some good old american blood, it was when i put on the new ignition stuff this season.


Bob 18436572 KaamaCat

You see I told you it was timed correctly! The biggest myth in engine assembly is that when you install the cam with the marks aligned the distributor is firing number one. Its not really that big a deal because who stabs a distributor with the timing cover off to see the marks anyway? Just rotate the engine untill you feel compression comming out of the #1 spark plug hole then keep going until the balancer reads 0 then stab at #1 cylinder.

Im glad it was something minor. Its probably good you broke the starter gear while working on the boat and not on the water. Good luck and go run that thing.

So Tinker, Lee, and Bluethunder who is right now!

Ron