Timing Problem

[harlowcl]

I have a 1978 140 mercruiser. I bought it last week, and cannot get it to run. There is spark and fuel, but it keeps backfiring through the exhaust. How can I give it the correct timing? I do not want to take the engine apart if possible.<br /><br />Any help would be apprieciated.<br /><br />Thanks

 

[harlowcl]

Re: Timing Problem

I just wanted to add that my compression is fine.

 

[WillyBWright]

Re: Timing Problem

Backfiring thru the carb would be more likely to be a timing problem. Flash it with a timing light and see where it is. It could be way retarded I suppose. Check your firing order and make sure the wires are connected correctly on the cap.

 

[Don S]

Re: Timing Problem

You have spark, but do you have GOOD spark. Bright blue and jumps about a 1/2"?<br />It may just need a tuneup. Plugs, points, condenser, cap, and rotor. Dwell set, then set the timing. A cracked distributor cap or moisture buildup inside the distributor can also cause the backfiring.<br />You are also going to need a service manual for your engine if you are planning on doing your own maintenance. You need Mercruiser service manual #3 part number 90-95693

 

[markvictor]

Re: Timing Problem

I would also check to make sure you do not have a stuck valve, which could be caused by sitting, or from water ingestion from a bad exhaust manifold...That's a 28 year old motor, I would check the exhaust as a matter of course anyway if you don't know when it was last checked or replaced....<br />Regards,<br />markvictor

 

[harlowcl]

Re: Timing Problem

I have a good spark and a repair manual. It probably is a valve problem. I just didnt know if there was any other way to check than to take the head.<br /><br />But if that is what I need to do, then I will. <br /><br />After all...it is winter time. Dont need the boat until March.

 

[Fishermark]

Re: Timing Problem

If your "compression is fine" then I doubt it is a stuck valve. Of course what "fine" means might be different to different people. What were your compression readings and how did you do them?

 

[Haut Medoc]

Re: Timing Problem

I would think that a bad valve would show up on a compression test. A collapesed lifter or a bad cam lobe might not.....I would try what Don S. & Willy suggest first & proceed from there....JK

 

[harlowcl]

Re: Timing Problem

Reading 120 in all cylinders. It should be 140. But for a 28 year old motor, I can handle 120. I used a compression gauge. Screwed it into the spark plug hole and cranked the motor. Turned it over about 5 times and took the reading.<br /><br />If it is not a stuck valve, what else could it be?

 

[Haut Medoc]

Re: Timing Problem

Timing......Do what Don S. says & proceed from there.....You just bought it.....This is where I would start ....JK

 

[tashasdaddy]

Re: Timing Problem

listen to these guys, they will save you money if you listen, be hard headed like me it will cost you first then you have to do what they recommend.

 

[markvictor]

Re: Timing Problem

Does sound like timing now that you clarify your compression readings, or firing order crossed up..

 

[Bt Doctur]

Re: Timing Problem

firing Order 1-3-4-2

 

[Don S]

Re: Timing Problem

You're real lucky, I have done compression tests on a lot of engines, and never had them all come out the same pressure on 4 cylinders in a row. Hopefully you don't have a gauge problem.<br />As far as firing order and timing, the firing order must also be going in the proper direction and starting out from #1 TDC on the compression stroke. If a previous owner took the distributor out and put it back in in a different location, it's very easy to move the wires to the new location. If you try to put the wires in the locations shown in the manual with the distributor installed in a different place, it ain't a gonna work my friend.<br />What manual do you have? Not a Clymers I hope. That alone would be enough to keep it from running.

 

[DHPMARINE]

Re: Timing Problem

Chris,I've only seen it once,but it dosen't mean I'll never see it again.<br /><br />Cam gear was fiber-toothed and had let go of the cam shaft,putting the whole thing out of wack.<br /><br />DHP

 

[harlowcl]

Re: Timing Problem

The manual I have is a Selco( I believe). I am at work right now, so I cant remember. I worked on the timing again last night with no luck. I guess I am going to take the timing chain/gear cover off and check the gears. I hope that is as far as I need to go.

 

[pine island fred]

Re: Timing Problem

Keep it simple before you tear it apart. Remove the valve cover, identify the intake valve for nbr 1 cyl. Find the tdc mark and bump the starter until the intake valve closes on the cyl. Bump some more as the pistion will be coming up on the compression stroke. Once at TDC the rotor should be pointing to nbr 1 plug position on the distributer cap. <br /> loosen and turn the distributer slightly in the direction of the rotor rotation, this will retard the timing and make the engine easyier to start. Old hand crank car had a lever on the steering colume to do the same thing. Also check that the rotor is in fact not damaged and has not slipped off the index land. Remote as it sounds, just got finished with a prestolite distributer whos flyweight springs broke and worked there way up to the cap and thru the timing way off. At first gave every indication that the timing chain had slipped. Good luck FRED

 

[Don S]

Re: Timing Problem

There is an easier way to find TDC on the compression stroke without pulling the valve cover. Remove the spark plug from #1 cylinder and turn the engine by hand while holding your finger over the spark plug hole until you feel compression building in the cylinder. once you fell compression building, continue turning till the timing mark lines up. You are then at #1 TDC on the compression stroke and you won't need a new valve cover gasket.

 

[Buttanic]

Re: Timing Problem

I just had a similar problem and it was a bad condenser. Before you start tearing things apart spend $2 for a new condenser.

 

[harlowcl]

Re: Timing Problem

I have another update for you. I started taking the motor out of the boat, along with the outdrive. The gimbal bearing was frozen to the shaft. I think that the cam shaft gears have some broken teeth. I plan to take part of the motor apart today.