Mercruiser won't start after rebuild

crs1500

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The manifolds in my 1998 305 Mercruiser were leaking badly, (went thru 2 starters form compressing water). After sitting for 3, 4 months I finally had time to tackle the problem, too late engine was frozen, replaced manifolds, added fresh water cooling system, and rebuilt heads with new valves. Put it together and can't get it to start. Had problems adjusting valves, book said after lash 360 degree turn, but too tight, and no compression had to loosen to bring compression up. I have compression of 100 psi, good spark and fresh gas. Any suggestions
 

Fishermark

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Re: Mercruiser won't start after rebuild

Well, you would have removed the distributor to do the work. It's possible you have it out of time.

Also - when you remove the lash - it is a very subtle thing to "feel" when the lash is totally removed. You need to move the push rod up and down and be careful to feel the exact moment the play is removed - then turn it down the additional amount.
 

crs1500

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Re: Mercruiser won't start after rebuild

Yes I have been trying to find the sweet stop, TDC, rotor pointing to number one, and number one cylinder in compression stroke. Spent most of yesterday trying to find the sweet spot.
 

crs1500

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Re: Mercruiser won't start after rebuild

Fishermark I agree with you it was pretty tricky to feel when the up and down lash was gone, I kept adjsuting and checking compression.
 

Don S

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Re: Mercruiser won't start after rebuild

Finding TDC on the compression stroke is easy to do.
Take all the spark plugs out so you can easily turn the engine by hand. Now, take your compression tester hose and stick it in #1 spark plug hole.
Start turning the engine either by hand or with a remote start button if you have the starter on it in the normal direction of engine rotation. With your thumb over the hole on the compression tester hose, turn the engine until you feel pressure building in the hose. From there, you don't need the hose any longer. Continue turning the engine in the normal running direction until the timing mark on the vibration dampner lines up with the 0 mark on the timing tab. You are now at #1 TDC on the compression (firing) stroke.
One note, when you line up the timing marks on the cam and crank when installing the timing chain. That is NOT #1 TDC on the compression stroke. it's #6 on your 305 Chevy. From there, put the distributor in with the rotor pointing to where you want #1 plug wire to be.
Also from this position you adjust the valves.
If you turn the crankshaft 1 complete revolution, you will be what most mechanics call 180 out. The rotor is now 180? from the #1TDC on compression stroke position.
 
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Re: Mercruiser won't start after rebuild

Exactly what Don says: :rolleyes:

This is my version:

I have found TDC by having someone rotate the engine by the crank bolt with a ratchet and socket by hand, while I had thumb over spark plug hole until u feel air pressure being pushed out the hole, continue to rotate the engine to the timing mark , should be close. That should be #1 TDC on compression stroke. But the timing calls for 4-8 "or so" before TDC so I would go past the mark the correct degrees of what timing calls for and drop dristributor "exactly" on #1 cylinder. Sometimes takes a few tries, you may have to rotate the oil pump drive shaft below with a long flat screwdriver to get it aligned.

When the timing mark is at the "0" you will be BEFORE TDC on the distributor. this way, Right from the start timing can be correct and fire right up.

Place tape on the distributor just below the cap at the #1 cylinder and mark the center line of #1 on the tape with a marker. So when you remove the cap to see the rotor you know were it should be pointing.
 

crs1500

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Re: Mercruiser won't start after rebuild

Don, Eric I set TDC with the intake manifold off neither valve was moving when at TDC.
 

rodbolt

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Re: Mercruiser won't start after rebuild

with the intake off its even easier, rotate the engine in its normal direction,watch when #1 intake valve closes and continue to the TDC marks line up.
 
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Re: Mercruiser won't start after rebuild

The intake valve draws in air to the cylinder so it can be compressed and ignited then the exhaust valve opens to let it out.

I never paid attention to the valves when getting TDC, (which I've always done 1st), then set the valves afterwards. If you've done It the way Don or I mentioned then the timing is not the issue with not running.
 

crs1500

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Re: Mercruiser won't start after rebuild

Will set timing accoring to Don and Eric's recommendation and see if that is the problem.
 
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Re: Mercruiser won't start after rebuild

You don't even have to pull the distributor to confirm it. Mark the distributor with tape just under the cap like I mentioned earlier, pull the cap to expose the rotor. Remove the spark plug for #1 cylinder (or all to make turning easier) rotate engine in correct rotation till u feel air pressure at that spark plug hole. and continue rotating engine to mark on balancer at zero. Rotor should be a little before the mark on the tape where the #1 plug boot is.
Good Luck,
 

crs1500

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Re: Mercruiser won't start after rebuild

Eric, did like you mentioned and the timing is where you mentioned, just before #1 on dist cap.
Still can't get it to start, do you think I should move the dist one tooth back or fwd and try.

Chris
 

Bondo

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Re: Mercruiser won't start after rebuild

Still can't get it to start, do you think I should

Ayuh,... I think you should start at the Beginning,....

It takes Fuel, Fire,+ Compression at the right Time to run....

You've got marginal Compression at 100psi...
Is it getting any Fuel,..?? Look in the carb,...
Is it getting any Fire,..?? Check at the sparkplugs,...
Then worry about the Timing...
 

crs1500

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Re: Mercruiser won't start after rebuild

Bond-o, yes squirting gas at carb, spark at plugs, compression low due to water in combstion chamber and ring sticking, should get better once started, if I get there.
 

Bondo

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Re: Mercruiser won't start after rebuild

Ayuh,... Put a timing light on it...
 
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