Down on power after engine rebuild |
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Waternut
Senior Member Joined: July-11-2012 Location: Macon, GA Status: Offline Points: 292 |
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Posted: April-14-2015 at 9:58pm |
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So long story short, I rebuilt my 86 351w engine over the winter. The engine got a new +0.030" bore, new pistons and rings, the crank ground -0.010", and a complete valve job. Obviously all the bearings were changed with the appropriate size as well. The only thing that wasn't totally reworked was the camshaft but it was in good shape and I replaced the camshaft bearings anyway. I also replaced the seals on my 1:1 borg/warner transmission and put new fluid in.
I finally got it out on the water today and it feels sluggish. The timing is 8 degrees before TDC at idle. I ran it around a little while fairly gingerly. Occasionally, I'd nail it for a brief time and it'd come up to speed slower than normal. When it hits 3200 rpms, it gives a small surge of power every time but is a good 4-5mph shy of my pre-rebuild top speed. Does the engine need more break-in time? Maybe secondaries on the carb opening (can't check this on my own)? Other ideas? I rebuilt the carb last year so I felt it should still be good and didn't touch it this winter. |
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jpage
Newbie Joined: July-16-2014 Location: Atlanta,GA Status: Offline Points: 29 |
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I like to run mine at 10* advance, i would check the carb, and look for vacuum leaks, What distributor are you running?
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JoeinNY
Grand Poobah Joined: October-19-2005 Location: United States Status: Offline Points: 5698 |
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Check your compression to make sure you dont have a stuck valve or something serious but after that I would guess you got your spark plug wires crossed somewhere? What you describe cannot be attributed to normal break in - sounds like you are down one or more cylinders
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Waternut
Senior Member Joined: July-11-2012 Location: Macon, GA Status: Offline Points: 292 |
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I stand corrected, I was actually at 12 degrees at 700 rpms in gear. I backed it down to 8-9 degrees. Must've been running lower rpms in the driveway initially.
I'll check compression tomorrow. I must've checked the spark plug wires about 10 times during install but it's very possible I was misreading or misthinking so I'll check them again tomorrow. I want to say the distributor is a mallory but can't remember for sure. It has the Prestolite electronic conversion so no points. |
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Mountain Man
Senior Member Joined: May-09-2014 Location: Brevard, NC Status: Offline Points: 124 |
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Waternut - Your base timing should be about 8 degrees BTDC to crank it and then adjust the timing using a light after it fires. If down on power I would verify the that the firing order is correct and that you have not crossed a couple plug wires. If after doing this it's still down on power - pull the spark plugs and look for any that are different in color from the rest - either wet with gas - or sooty - or oil soaked. If nothing shows itself on the plugs start systematically eliminating the simple cheap stuff first: fuel pump (check the pressure), fuel filters, clogged flame arrestor, old gas, etc.........
Good luck, Steve |
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SNobsessed
Grand Poobah Joined: October-21-2007 Location: IA Status: Offline Points: 7102 |
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There is a paperclip trick to tell if the secondaries are opening. It's described somewhere on the site, a search may find it.
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Ben Franklin |
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mamigacz
Groupie Joined: June-08-2014 Location: Wisconsin Status: Offline Points: 96 |
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If you used the old cam and lifters did you make sure to mark the lifters and install them in the bores they came out of? If you replaced the lifters with new, did you go through the break in process when starting the engine for the first time? |
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Waternut
Senior Member Joined: July-11-2012 Location: Macon, GA Status: Offline Points: 292 |
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Thanks, I actually found the paperclip trick last night and plan to try it today.
I did reuse the old lifters and they were put back in the same place they came from. I shimmed accordingly to get the proper preload on each valve. The push rods were also put back in the same place. The rocker arms weren't because the shop doing the valve job threw them all in a big box which I didn't appreciate but he swears it doesn't matter where they go. |
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phatsat67
Grand Poobah Joined: March-13-2006 Location: Indiana Status: Offline Points: 6157 |
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Yeah, rockers shouldn't be a huge issue. I reused all of my valve train from cam to rockers and they all went back in their exact spots with a nice amount of assembly lube.
The only really critical point is that each lifter goes back where it was originally at. |
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Bri892001
Grand Poobah Joined: September-27-2008 Location: Boston MA Status: Offline Points: 4947 |
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One free check, make sure nothing is funny with the throttle cable. In other words, make sure the cable is operating such that if full opens the carburetor throttle.
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Waternut
Senior Member Joined: July-11-2012 Location: Macon, GA Status: Offline Points: 292 |
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Good call. That whole linkage was disconnected so it may not have gone back together exactly right. |
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mamigacz
Groupie Joined: June-08-2014 Location: Wisconsin Status: Offline Points: 96 |
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It wouldn’t hurt to check if the distributor is advancing correctly. I assume you have a timing light, right?
Procedure: Ignore steps 1 thru 4 if your harmonic balancer has timing marks that go up to 34 degrees (or close to 34 degrees). 1) Find out the diameter of the harmonic balancer. I think it’s 6.375 inches. 2) Calculate the tape cut length according to the below equation: (harmonic balancer diameter) x 3.14 x 36 / 360 = tape cut length in inches For example: 6.375” x 3.14 x 34 / 360 = 1.90 inches 3) Cut off a piece of masking tape (or electrical tape) to the length calculated above. 4) stick it to the harmonic balancer like the view below One end of the tape will be at 0 degrees BTDC and the other end will be 34 degrees BTDC. With 12 degrees of initial advance, you should be getting approximately 34 degrees of total advance. If you want, you can do this on the trailer in neutral: 5) hook the timing light up 6) start the engine 7) point the timing light at the timing pointer. 8) slowly rev the engine to around 3000 RPM and watch the timing move. It should max out close to the end of the tape marked 34 degrees. 9) all the advance should come in around 3000 RPM. If it doesn’t, note what RPM it maxes at. Post your results and we can discuss if something is wrong or not. |
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Waternut
Senior Member Joined: July-11-2012 Location: Macon, GA Status: Offline Points: 292 |
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I have been using a timing light. It's a steady 8-9 degrees at idle in gear. I didn't check the timing at 3000rpms but it's probably 15 degrees at 1500 rpms so it does go up. I can verify later tonight what the timing maxes at.
I changed the distributor springs a year or two ago because the timing was bouncing all over the place and that was just caused by over stretched springs allowing the weights to flop around. |
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mamigacz
Groupie Joined: June-08-2014 Location: Wisconsin Status: Offline Points: 96 |
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Your symptoms sure point to an ignition problem. The power surge at 3200 almost sounds like a fouled plug that is starting to fire intermittently. I'm curious on the results of the plug conditions. |
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Waternut
Senior Member Joined: July-11-2012 Location: Macon, GA Status: Offline Points: 292 |
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They are brand new plugs. I've seen plugs on more than one occasion split and/or fail completely shortly after installation so that could be a possibility.
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Waternut
Senior Member Joined: July-11-2012 Location: Macon, GA Status: Offline Points: 292 |
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Ok so here are the findings so far. I checked the compression and all cylinders are at about 118psi which seems really low for a fresh rebuild with GT40p heads. Should I be checking with all plugs installed or removed? I was testing with all plugs installed. All the plugs look normal and none look cracked, black, wet, or anything like that. Plug wires are hooked up correctly. I'm using 18456273 as the firing order with the distributor spinning counter clockwise. 1 being the front of the drivers side and 5 being the front of the passenger side.
I started the day running slightly weaker than yesterday and noticed the secondaries were not opening. The diaphragm appeared to be pulled in but could've pulled itself in when I pulled the cap off. Either way, there are no holes or tears and after hooking it back up, it opens fine. After a little while, the engine started sounding bad and wouldn't even rev to 3000rpms in neutral. It was really surging like crazy too. Turns out the wires I soldered for the prestolite electronic ignition had poked through the shrink wrap and were grounding against the engine. Fixed that issue and it runs a little better than yesterday with the secondaries opening but it's still weak and lacks a lot of power. Engine vacuum at the intake manifold jitters between 16-17 in-Hg but I'm using a vacuum gage meant for composite work so I don't know if the jitter is a vacuum jitter or a vibration jitter from the engine. The timing seems to top out around 25 degrees but that is a guess because once I pass about 1800rpms, all the numbers disappear. The numbers go up to 30 but after about 1800rpms, it just looks like the numbers got wiped and I'm guessing off of the stamping on the forward side of the harmonic balancer. Not sure if that's a timing light failing/can't keep up or whether that means there is some major timing issue. |
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Waternut
Senior Member Joined: July-11-2012 Location: Macon, GA Status: Offline Points: 292 |
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Found this inside the distributor located underneath the rotor on the lower plastic ring. It's very small and magnetic but I can't find any place where it might go on the cap, rotor, inside the distributor, or even in the prestolite ignition piece.
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mamigacz
Groupie Joined: June-08-2014 Location: Wisconsin Status: Offline Points: 96 |
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-The firing order is correct for reverse rotation 351W.
-I wouldn't be too concerned on the compression readings. What would be more concerning is if one of the cylinders was 10 PSI (or more than 10) lower than the rest. -You have to check all the plugs. -That piece you show in the picture, looks like a magnet from the pick-up stator. There should be 8 magnets total. Pull your rotor off and you should see a black ring at the base of it (if its a pertronix kit). That ring should have no missing magnets in it. See the view below. It has red arrows pointing where the magnets would be. |
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Waternut
Senior Member Joined: July-11-2012 Location: Macon, GA Status: Offline Points: 292 |
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All the plugs look fine.
The magnet was found on top of that black ring after pulling the rotor off. Do those magnets tell the coil to send spark? |
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Gary S
Grand Poobah Joined: November-30-2006 Location: Illinois Status: Offline Points: 14096 |
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To properly do a compression test you need a fully charged battery,warmed up,all plugs removed and throttle wide open. Why not remove the pertronix and reinstall the points and see what happens?
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phatsat67
Grand Poobah Joined: March-13-2006 Location: Indiana Status: Offline Points: 6157 |
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What Gary Said
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mamigacz
Groupie Joined: June-08-2014 Location: Wisconsin Status: Offline Points: 96 |
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Yes If you are missing a magnet, one of your plugs is not firing. Did you look at the stator ring to see if any are missing? |
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Waternut
Senior Member Joined: July-11-2012 Location: Macon, GA Status: Offline Points: 292 |
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I bought this boat with the Presolite ignition. So I've never had the points setup nor have I ever worked with a points setup to know what I need to build that system up or even set it up properly. I'm sure it's not that difficult and I could figure it out but without the parts on hand, it's not a quick and dirty swap.
I looked all over the cap and rotor figuring that's where it came from but I never saw anything else that resembled one of those magnets. Would replacing the rotor give me all the parts I need or do those lower rings come separately? |
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mamigacz
Groupie Joined: June-08-2014 Location: Wisconsin Status: Offline Points: 96 |
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The lower ring (pick up stator ring) comes with the pertronix kit. I know on mine (clip sytle distributor cap) the rotor is also part of the pertronix kit. The stock prestolite rotor will not pilot the stator ring properly.
Before you replace any parts, remove the cap, rotor and stator ring. Take pictures of all these parts. Also, take pictures of the pertronix ignitor. Post the pictures so we can see the condition. |
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Waternut
Senior Member Joined: July-11-2012 Location: Macon, GA Status: Offline Points: 292 |
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So the magnet did fall out of the stator under the rotor. I put it back in and the engine ran great. Thankfully I didn't chuck it.
With that success comes more problems though... I reset the timing to 10 degrees at 750 rpms. I warmed the engine up normally and then ran it hard for a minute or two. Stopped and double checked the timing. After that short run, the timing was around 23-24 degrees at 750 rpms. I backed it down again and idled over to a friends dock who came out to talk for 10-15 minutes. After that, I ran it hard again and 30-45 seconds the engine started surging and eventually got so bad I backed off and the engine died completely. It felt like it was down a few cylinders at this point so I limped it home and the timing was at 5 degrees retarded. Checked the spark plugs... #4 looked black and sooty, #5 and #6 looked bright white and nearly brand new. The rest looked good. Set the timing again and it still ran like crap and would barely rev in nuetral. 20 minutes later, it ran good again. Sounds like a coil issue to me but not sure. The timing drift makes me think the electronic ignition (Pertronix Ignitor) is going bad. 20 minutes later |
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Bri892001
Grand Poobah Joined: September-27-2008 Location: Boston MA Status: Offline Points: 4947 |
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I'm not sure if timing drift is a symptom of a bad ignitor or not. Maybe others could speak to that. The first thing that comes to my mind is that one of the advance springs is broken. The springs are supposed to allow the weights to move out with increased RPM, thus advancing the timing. And, just as important, to pull the weights back in as the Revs go down, bringing the timing back down to normal. |
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GottaSki
Grand Poobah Joined: April-21-2005 Location: NE CT Status: Offline Points: 3359 |
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I concur with Brian, mech advance is sticking or a spring is sloppy or broken.
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"There is nothing, absolutely nothing, half so much worthwhile as messing around with boats...simply messing."
River Rat to Mole |
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Waternut
Senior Member Joined: July-11-2012 Location: Macon, GA Status: Offline Points: 292 |
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Springs are in good shape and the weights move in and out properly. I checked that a day or two ago. They could be sticking but when I'm at the dock, the timing goes up and down smoothly. I'll lube them up to make sure they aren't getting stuck somewhere.
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phatsat67
Grand Poobah Joined: March-13-2006 Location: Indiana Status: Offline Points: 6157 |
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Toss that ignitior junk. It's been beat like a dead horse. You can A) buy a pcm electronic ignition or B) Put a DUI in it.
Confirming ignition is in proper working order is always the first step to success. You need spark/fuel/compression. You have confirmed you have compression so move to ignition. |
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Gary S
Grand Poobah Joined: November-30-2006 Location: Illinois Status: Offline Points: 14096 |
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+1 seems like more than 1 has been bad lately
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