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rebuilt 454 seems to run very rough

M

markwright

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I recently installed a rebuilt crusader 454 in to my Mainship. the motor will fire right up but seems to idle very rough. I will alter the rpm and the idle will seem to get smoother then I will change the RPM and it gets rough again. I replaced the plugs and wires with the rebuild. I have sprayed WD 40 around the intake and the carb looking for vacuum leaks and none were found? i am not sure what to check next? Right now the motor is only timed by ear....I was planning to get the timing light on it when the boat is in the water. even wtih that though I cant imagine it would run the way it does??
 
Have somebody verify the plug wires are 1) installed correctly (fully seated) and 2) are in the proper firing order (no crossed wires).

You also need to have the ignition timed with a light before going much further....be good to verify the advance works, too, after you get the distributor positioned correctly.

Actually, you should complete the rest of the tune up steps to get the rebuild off to a good start on life...
 
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I do want to get the timing light on there so I know that is all set. All the wires are on and from what i can tell the order seems right on. I was wondering if possible the dist is off by a tooth?? I was also thinking that if a wire was croseed it would not smooth out at some rpm's? let me get the timing light on it and at least confirm that.....then we will see!
 
Did you do the rebuild?? We put in a rebuild last year and after trying everything to get it to smooth out we found that the mechamnic had NOT set up the valves. Adjusted the valves and she runs smooth as silk.
 
no I have only started the motor and ran it for a short time. once it hits the water I am planning to break in according to what I have read from crusader....varying RPM under load above 1200 rpm. I am just worried about how rough it is....
 
well the boat is in the water and i have had a chance to run it under load. the motor has a very noticable shake. i ran it between 1200-2200 rmp and the shake does not go away. it seems better at some rps's than others but does not go away. I am really wodering about the chance that the valves are not adjusted properly?? how do i confirm that short of just taking the valve covers off and doing it? in nuetral i have revved it up to 2700 and it seems to actually smooth out. i didnt do that long though not wanting to damamge the motor.
 
I'd suggest getting a vacuum gauge. may be bad adjustment but a crossed pair of ignition leads (or a bad lead or one not fully seated on the plug) are likely, too.
 
I rechecked the plugs and wires last night and everything seems good. all are new but of course always a chance of a defective one I guess. As far as the vacuum gauge I have not tried that yet. where would I hook up too? what is the reading supposed to be on it? I am try that tonight....
 
There's a www site that has some graphics of what to look for...think it is called 'secondchancegarage.com'. do some www searching and I'm sure you'll find it.

You can attach it via the intake manifold plug, with an adapter. I usually use the choke pull-off hose on the carb as it has a direct path to manifold vacuum.

"seems good" will cause wasted time -> you need to be sure. Sometimes, getting another set of eyes to give it an independent look is worth the cost of a few cold ones.

Also, FastJeff's 'pull the plug wires one at a time' method can isolate the problem cylinder. I've found it most productive to have the engine loaded when doing this test. Search this forum for more details.
 
I actually did have another person look over it too. the wires are all going to correct spot and the boots are all seated. I was wondering about pulling each wire one at a time. I did it at idle but really could not tell much difference. I would think that under load it would be more evident. I will start by redoing the timing tonight and checking the vacuum if i can get my hands on a gauge. We will see!
 
Do the pull each wire test one more time, but this time have her idling at 1,500 rpms. ANd make sure it's warmed up.

Jeff

PS: One more thing you can try (if the above test tells you nothing): Take it for a ride, push it some, then cut the motor off fast as you can. Drop the hook, let her cool, then pull all the plugs and read their colors. All of them should be light colored. If you find one that/s black, start investigating.
 
that is intersting. I will try the other items first and see how I make out. I really have not pushed the motor at all since it is so new and since the shake is occuring. Under load only got up to 2200 so far. i will keep you posted. thank you for all the great feedback!! hopefully I will get to the bottom of this one way or another. it is so tough since basically everything was repalced.
 
Still having the shake. I did pull each plug wire while the engine was at a fast idle and it actually didnt really do much. It was strange the engine still ran about the same with 1 wire at a time pulled. I had the person I got the motor from (sold it to me didnt build it himself) come down and look and he is a little stumped for now as well. He pulled the valve covers and checked the rockers and said that they are non adjustable? I did not know that was a option on a GM 454? the company he got the motor from wants him to check compression next. good times......
 
..."It was strange the engine still ran about the same with 1 wire at a time pulled."

HuuuuHHH! That's a definite clue as to what's going on. It tells me that NONE of the cylinders are doing much. (Why? You got me. Sorry.) That would also explain why the motoir isn't making much power in gear.

Jeff

PS: Are youi absolutely sure the motor is timed right? If it was retarded that would be the result.
 
Non-adjustable valve train - that's an indicator you have a GenV/VI class of engine. The older Mark IV's have an adjustable valve train.

Compression check would be good though I'd hope that's not the issue (banking on the rebuilder being competent). You mentioned new plugs and wires but didn't say anything about the cap & rotor. Old points style distributor or the newer electronic type? Visual inspection of the carb yet? Note the plugs' color and condition when you do the compression check...I'd suspect they are black from carbon - are they wet (see if they have a fuel odor, too) or dry.
 
the timing is set right now to 8. the cap and rotor were replaced along with the wires. I am hoping of course the compression checks out that will be looked at tonight. the carb was rebuilt before it went back on the motor but of course there is always a chance that something went wrong on that?? I just keep having this though what if I didnt line up the flywheel correctly would that cause this try of shake? I remember being very careful and setting it up but what if......
 
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I just keep thinking what if i rotated it around and that blank dowel is not lined up?? I remember looking at it but who knows? whould that send it out of balance?
 
Since I don't see this listed, here goes: Do you have a Delco EST distributor? and if so, after timing, did you flip the TIME/RUN plug back into RUN ?
 
You can visually inspect the flywheel by removing the timing plug on the flywheel cover...should be pretty obvious. I'd think you know it if the flywheel was loose when you went to start it.

If what you HAD was the older Mark IV block and you now have the newer GEN type, you may want to get the proper specs from the rebuilder
 
I have the prestolite dist on the motor. I do not see any plug to remove when i set the timing on that one? I know the other motor was set to 8 so that is what I did on the new motor. Figured 8 or 10 would be close enough to have it run ok. I dont doubt the flywheel is tight.....just worried it maybe was not on the same as it came off. it does make sense that the shake would get worse with speed though.....
 
The prestolite isn't an EST so you won't have the timing plug. Now for the bad news....

If the old engine was a Mark IV block and you put it's flywheel on the new block (GenV/VI, with the non-adjustable valve train), that's the likely source of the shake. Bolt patterns are the same but the balancing required is different. From what I've found, the best fix is to get a new GenX flywheel vs getting the old one rebalanced. Many posts on other sites on this topic. You may wanna research this a bit more before proceeding.
 
http://reviews.ebay.com/Big-Block-Chevy-quot-Generations-quot-A-primer_W0QQugidZ10000000001563647
This reads like the Gen7, 8.1 liter is the first to go to an internally balanced crank, meaning both the flywheel and the harmonic balancer would be different from the earlier engines.
The Gen V is regarded as a cost reducted MarkIV, not highly regarded,mostly related to the non-adj valves. It's also an orphan with regard to the heads/head gaskets. It's not yet a roller valve train; there is no good technical reason to use the Gen V. The one-piece oil seal is arguably better.
 
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