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Unread 03-24-2009, 10:14 PM   #1
TBrock
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I-6 issues after rebuild

One of my neighbors just rebuilt his engine and is having an issue on start up and I'd like input from y'all.

It starts and runs but has a steady, rhythmic pop coming from the carb. It sounds like it is spitting back through the carb every time one cylinder fires. He says it is really low on power and won't run when he gives it throttle.

I initially figured he had a stuck intake allowing it to exhaust through the carb when it fired. He pulled the valve cover off and found one push rod laying loose but no evidence of a stuck valve (not sure how he checked).

I was thinking misaligned timing chain but realized this would affect ALL cylinders. I'm leaning towards a bent or stuck valve.

Advice, wisdom and counsel?

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Unread 03-25-2009, 06:53 AM   #2
Mike Romain
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Sounds like he maybe got his timing wrong. They will run at 180 off, but have no throttle.

Folks get caught because #1 piston has 'two' top dead centers or TDC, one is on the exhaust stroke and the other is on the compression stroke. To get the right one, he needs to pull the plug and hold his finger over the hole as he manually turns the engine. When he is on the right revolution of the crank, he will feel compression.
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Unread 03-25-2009, 10:35 PM   #3
TBrock
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Quote:
Originally Posted by Mike Romain View Post
Sounds like he maybe got his timing wrong. They will run at 180 off, but have no throttle.

Folks get caught because #1 piston has 'two' top dead centers or TDC, one is on the exhaust stroke and the other is on the compression stroke. To get the right one, he needs to pull the plug and hold his finger over the hole as he manually turns the engine. When he is on the right revolution of the crank, he will feel compression.
He originally had it reversed and it wouldn't run. The above symptoms are after swapping the wires (easier than resticking the dist)
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Unread 03-26-2009, 06:01 AM   #4
Mike Romain
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Quote:
Originally Posted by TBrock View Post
He originally had it reversed and it wouldn't run. The above symptoms are after swapping the wires (easier than resticking the dist)
He needs to try again, sounds like 2/3 off.... or one plug wire. I have sen this happen after a rebuild, there are a few combinations that can happen.

The person I was helping just had to bite the bullet and start over with things in the right place.
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86/00 CJ7 Laredo, 33x9.5 BFG AT's, 'glass nose to tail in '00, 'New' frame,wires and plumbing in '09. Carter BBD Carbed 4.0 HO in '10.
89 YJ Renegade. BBD Carbed 4.0 HO. Locked front and rear with 33x9.5 BFG AT's
Some Canadian Bush Jeep Runs and Build Photos: http://mikeromainjeeptrips.shutterfly.com (10 new albums added Sept 16/10)
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Unread 03-26-2009, 04:15 PM   #5
TBrock
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Quote:
Originally Posted by Mike Romain View Post
He needs to try again, sounds like 2/3 off.... or one plug wire. I have sen this happen after a rebuild, there are a few combinations that can happen.

The person I was helping just had to bite the bullet and start over with things in the right place.
I've verified the firing order but will check it again. Anything else? I was thinking bent valve.
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Unread 03-26-2009, 05:11 PM   #6
Fjguercio
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Quote:
Originally Posted by TBrock View Post
He originally had it reversed and it wouldn't run. The above symptoms are after swapping the wires (easier than resticking the dist)
NOPE... can not do that. It will not run right. Need to start over with TDC compression on #1 and insert the distributor. It will not run right 180 our of position.

I also just posted a wrong push rod information on a few current posts and the technical artilce section. The push rod lenghts vary by yr and that could be messing you up too.
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Unread 03-26-2009, 07:34 PM   #7
TBrock
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Quote:
Originally Posted by Fjguercio View Post
NOPE... can not do that. It will not run right. Need to start over with TDC compression on #1 and insert the distributor. It will not run right 180 our of position.

I also just posted a wrong push rod information on a few current posts and the technical artilce section. The push rod lenghts vary by yr and that could be messing you up too.
The wiring is phased to #1 at TDC its just that #1 is in a different position than what is shown on the cap #s. So long as #1 was synced to TDC and the rest are in the correct order, you can set the dist into the block however you want. The typical problem this causes is the vacuum advance hits things when setting the timing, it won't affect anything else as long as the firing order is correct and #1 was set at TDC. That's all good.

He reused the original pushrods, so unless they are different lengths between exhaust and intake, he should be fine there. Assuming non are bent. He also reused the original valves and didn't check any of the guide clearances, valve straightness, etc. I'm thinking he may have a sticking valve (bent or clearance issue) that is allowing combustion back through the carb. If it was a timing issue, it would affect more than one cylinder.

I'm just hoping someone can think of something else that I'm missing. I hate for this guy to have to go back into the engine. He's a fairly jr. military guy so money is tight. I'm short on spare time so I can't pitch in as much as I'd like.
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Unread 03-26-2009, 08:29 PM   #8
Fjguercio
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Quote:
Originally Posted by TBrock View Post
The wiring is phased to #1 at TDC its just that #1 is in a different position than what is shown on the cap #s. So long as #1 was synced to TDC and the rest are in the correct order, you can set the dist into the block however you want. The typical problem this causes is the vacuum advance hits things when setting the timing, it won't affect anything else as long as the firing order is correct and #1 was set at TDC. That's all good.
NOPE,, JeepHammer has posted will not run right 180Deg out. Do not agree with you.

Quote:
Originally Posted by TBrock View Post
He reused the original pushrods, so unless they are different lengths between exhaust and intake, he should be fine there. Assuming non are bent. He also reused the original valves and didn't check any of the guide clearances, valve straightness, etc. I'm thinking he may have a sticking valve (bent or clearance issue) that is allowing combustion back through the carb. If it was a timing issue, it would affect more than one cylinder.
The lifters can take up .030" of valve trane wear. Did not look at the mileage but the rocker arms and push rods get that amount of wear easily with 25 yr old engines. Foolish not to replace those. Then if the valves do not open far enough the engine does not breath right. In addition as these push rods and rocker arms wear the oil path holes may not line up properly. Further your new lifters are now wearing on an old push rod. On an old engine I would replace these parts, push rods & boats, before I would replace a lot of other stuff trying to get the wear out of the top end.

Sorry we are not agreeing
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Unread 03-26-2009, 09:32 PM   #9
gosupes
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Quote:
Originally Posted by Fjguercio View Post
NOPE,, JeepHammer has posted will not run right 180Deg out. Do not agree with you.
The dizzy can be inserted 180 (or anything degrees out for that matter) out then the wires can be re-indexed staring with the #1 and working your way following the firing order. Recheck with a timing light and it will run fine. People do this all the time in order to make room for the vac advance port. Instead of picking the dizzy up and rotating a tooth or two, they with move all the plug wires one or two spots over, turn the dizzy and reset the ignition timing.

If a bent or stuck valve is suspect, the best check is a leak down test. If there is a stuck valve, you will hear air escaping through either the exhaust or intake manifold.
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Unread 03-27-2009, 06:44 AM   #10
Mike Romain
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Quote:
Originally Posted by TBrock View Post
I've verified the firing order but will check it again. Anything else? I was thinking bent valve.
He needs to start over. If he got the distributor wrong, the timing chain is also suspect, they are 'very' tricky to get right. Folks don't do the last test of making 'really' sure there are only the right number of chain link pins between the marks....
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86/00 CJ7 Laredo, 33x9.5 BFG AT's, 'glass nose to tail in '00, 'New' frame,wires and plumbing in '09. Carter BBD Carbed 4.0 HO in '10.
89 YJ Renegade. BBD Carbed 4.0 HO. Locked front and rear with 33x9.5 BFG AT's
Some Canadian Bush Jeep Runs and Build Photos: http://mikeromainjeeptrips.shutterfly.com (10 new albums added Sept 16/10)
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Unread 03-27-2009, 06:41 PM   #11
TBrock
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Quote:
Originally Posted by gosupes View Post
The dizzy can be inserted 180 (or anything degrees out for that matter) out then the wires can be re-indexed staring with the #1 and working your way following the firing order. Recheck with a timing light and it will run fine. People do this all the time in order to make room for the vac advance port. Instead of picking the dizzy up and rotating a tooth or two, they with move all the plug wires one or two spots over, turn the dizzy and reset the ignition timing.

If a bent or stuck valve is suspect, the best check is a leak down test. If there is a stuck valve, you will hear air escaping through either the exhaust or intake manifold.
Duh! Leak down test! I'll try that. May have to roll my compressor up the street...
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Unread 03-27-2009, 06:43 PM   #12
TBrock
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Originally Posted by Mike Romain View Post
He needs to start over. If he got the distributor wrong, the timing chain is also suspect, they are 'very' tricky to get right. Folks don't do the last test of making 'really' sure there are only the right number of chain link pins between the marks....
Yeah, I was really worried about the timing chain too but figured if it was off enough to cause this, it would do it on every cylinder. It does cover ALL of the other symptoms. Probably do the leak down first.

Thanks guys!
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Unread 03-27-2009, 06:48 PM   #13
TBrock
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Originally Posted by Fjguercio View Post
NOPE,, JeepHammer has posted will not run right 180Deg out. Do not agree with you.



The lifters can take up .030" of valve trane wear. Did not look at the mileage but the rocker arms and push rods get that amount of wear easily with 25 yr old engines. Foolish not to replace those. Then if the valves do not open far enough the engine does not breath right. In addition as these push rods and rocker arms wear the oil path holes may not line up properly. Further your new lifters are now wearing on an old push rod. On an old engine I would replace these parts, push rods & boats, before I would replace a lot of other stuff trying to get the wear out of the top end.

Sorry we are not agreeing
Me to since I've stuck distributors into two different jeeps and then simply indexed the wires so that the #1 wire was over the rotor and the rest just followed the firing order. They seemed to run fine. I've also done this on my 455 pontiac and several SB chevys.

As for the rest, young guy, pregnant wife and not a lot of money. Penny wise and pound foolish. I got involved after the engine was back together and he couldn't get it to run.
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