maybe cam problem please help

[Reel Poor]

Re: maybe cam problem please help

Cranking with a plug out is another sign that the exhaust is restricted SOMEWHERE. I started to tell you to try cranking it with a spark plug removed when I posted in your other thread.

 

[Coors]

Re: maybe cam problem please help

I missed that one, reel. so many threads,,,

 

[Coors]

Re: maybe cam problem please help

Yeah, we need compression #s on each cylinder, and intake vacuum #s, this is strange

 

[badbowtie]

Re: maybe cam problem please help

I can check compression on each cylinder today when I get home. I do not have a way to check intake vaccum.

 

[SuperNova]

Re: maybe cam problem please help

I'm still betting that the cam timing is off by a tooth and the no start is caused by the extra backpressure. My friend had a camaro one time that intermittently would not start, even on starting fluid. It had good spark, but slightly low compression even though it was a brand new motor. We finally decided that the cam was too aggressive and bleeding off too much combustion pressure, so he decided to replace it. Lo and behold, when he got the timing cover off and aligned the marks in preparation for removal, he discovered the cam was off by a tooth. He adjusted the timing and put it back together, compression was up and he hasn't had a problem with it since. Course. I've been wrong before.
--
Stan

 

[John_S]

Re: maybe cam problem please help

It would be nice if there was an easy way to validate the gears being off by a tooth, before going into all that work. Depending on the boat, it may be a real hassle. Outside of a degree wheel, dial indicator, and known cam specs, I don't know of a way. And that method isn't easy or quick

I did a quick re-pass through the thread. While it has probably been done, I didn't see it mentioned. Has the base timing been checked? Should be able to do on the muffs. Would also adjust idle mixture. If not checked, probably the last of the simple things.

 

[Reel Poor]

Re: maybe cam problem please help

The problem your having is due to excessive back pressure.

(1) Restricted exhaust somewhere
(2) Cam timming
(3) Maybe valve adjustment
(4) Bad cam

 

[paulrfrancisco]

Re: maybe cam problem please help

Would the cam being off a tooth show up with a timing light? Also the previous owner stated it was a mild race cam... maybe this was their cover story for a bad assembly job where they couldn't figure out the issue... but when it runs on the trailer it sounds a little aggressive cause its advanced?

Mmmmmm

 

[Reel Poor]

Re: maybe cam problem please help

Would the cam being off a tooth show up with a timing light?

No.....A timming light shows ignition timming which is relative to piston position, not cam timming.

 

[Limited-Time]

Re: maybe cam problem please help

I think Reel Poor is on to something with his timing/back pressure theory. Check and verify the distributer to cam timing (assuming the cam to crank timing is correct). Remove the #1 plug and bring the engine to TDC on the Compression stroke. This can be done by placing your finger over the plug hole and turning the engine over, when you feel pressure building i.e air escaping through the plug hole the piston is on its way up on the compression stroke. Continue to rotate the engine until the timing mark is at TDC. Check the orientation of the rotor to make sure its pointing to the #1 position on the dist. Also make sure the firing order is correct 1-8-4-3-6-5-7-2. Then check the timing as per the manual. I have see cases where the dist can be one tooth off and the engine will still run at idle with no load.

 

[badbowtie]

Re: maybe cam problem please help

I have checked for top dead center on the distributer once I am going out to pull the valve covers and going to double check the rockers and going to double check for top dead center again then will be heading to the lake for some more tests.

 

[SuperNova]

Re: maybe cam problem please help

Before you run to the lake with it try this test: Hold your hand over the prop hub so you're blocking the exhaust flow, but not tightly, then try to start the engine on the trailer. The engine should start and push your hand off the prop. You may have to block off the two small ports up at the base of the transom fitting to be accurate, but I don't think it will be necessary. If it does start then you'll at least know it's not a back pressure problem or not likely cam timing and I would definitely look at the water issue end of things or tilt angle.

If it doesn't start, then you can pull your hand away and see if it starts.
If it does there should be a pretty reasonable amount of exhaust flow and pressure, if there isn't then it's exhaust restriction. If there is a good flow of exhaust then it's cam timing. Cam timing should have shown up during the vacuum test as low engine vacuum 11-18 in Hg versus normal 20-22 inHg.

Don't worry about rechecking all that stuff you said, you're past that point already.
--
Stan

 

[badbowtie]

Re: maybe cam problem please help

well i have not tried the hand over the prop yet I was already gone. I adjusted the valves which needed to be done anyway they had a small tap. I also installed a new module and coil in the distributor. It is still doing the same thing it just will not start in water.

 

[Dakota47]

Re: maybe cam problem please help

Sound like your boat is scared of the water. check the exhaust flappers. maybe one is stuck closed. you have a exhaust blockage somewhere. have you checked the outdrive yet? Pull it and see whats up.

 

[badbowtie]

Re: maybe cam problem please help

I have already removed the out drive I have had both flappers of and nothing is stuck. Once again last night I got to the lake backed straight into the water lowered the out drive and pumped it 2 times then left about 1/4 throttle and the boat started right up let it run for a minute shut it off and then tried to restart it. It would not start for nothing. I am going to stop at sears on my way home and buy a vaccum gauge were would you recomend me to hook it up I have never used one. Just a vaccum port on the carb. This is just so weird looks like another weekend that I will not get to use the boat unless I can figure something out tonight with the help of you guys.

 

[Limited-Time]

Re: maybe cam problem please help

The vaccume gage has to be plumbed in below the throttle plates in the carb. I would pull a manifold plug, (they are an NPT thread, usually with a square or allen wrench type drive) take it to an auto parts store and have them set up an adapter to get you to the correct hose-barb size for your vaccume gage. They will also have rubber plugs to seal off the barbed port when you remove the vac. gage.

 

[badbowtie]

Re: maybe cam problem please help

I can't see this hurting anything but On each valve cover I have a gutted out pcv valve that both go up to the air cleaner one on each side. That wouldn't have anything to do with my problems would it. Also if anybody has some thoughts that would like to talk to me over the phone You can email me with you'r number Or I can send you my number. Badbowtie@zoomtown.com

 

[SuperNova]

Re: maybe cam problem please help

no, that's pretty much normal; it's how they all are.
--
Stan

 

[badbowtie]

Re: maybe cam problem please help

I stoped on my way home today and bought a vaccum gauge you can never have to many tools. I was unable to try that tonight I have to go to the marine store tom. and buy a new mercruiser starter I burnt mine up last night at the lake trying to get it started. I also have a points style ditributer should I try to install it and remove the hei style that is on it. I hate to see what the starter is going to run me tom.

 

[Reel Poor]

Re: maybe cam problem please help

If you shop the net you can find them for less than 100 dollars. Don't put an automotive starter on you boat or you may have a KABOOM instead.

I don't believe changing the distributer is going to help with your problem.