Which broke 1st, chicken or egg?
 

Hi All!

Ok, odd issue the other day. Was out playing and had made several runs across the lake at speed, 5-7 miles max each way, then went and hung out at a dock for about an hour. While heading back at a cruise of about 4300-4500 rpm, the port motor shut off. No noise, no sputtering, it just turned off. Gauges looked fine.

Stopped and checked, and no spark at the coil. So limped home on one.

Its an MSD 6M-2L ignition box, and after going through the MSD troubleshooting, it looked like a bad box.

So, we replaced the box, fired up the motor, and still no spark? Obviously we thought that was odd, so went back though the MSD procedure again, and with the jumper wire, we got a killer spark. But no spark when turning over the motor.

Long story short, the timing chain was broke. Reasonably new motors, less than 100 hours, and very high quality parts.

Has any one seen a MSD box send out odd signals as it was dying that could cause a chain to break? I can't see how a chain breaking could cause a MSD box to go out. But it seems very unlikely that they would both fail at the same time without being related.

Any one ever heard of anything like this? Any thoughts?

I was in a friends single engine boat when something similar happened. We were cruising at about 50 when it shut off. Didn't make a sound, it was like you shut the key off. When we found no spark, we assumed an ignition problem and got towed in. Turns out there was no spark due to the distributor not turning - the chain was broke. It was due to regular length lifters being used in a big m block. It had some run time on it, but eventually a link bar broke off leading to the chain breaking. It doesn't explain the msd problem, but I would definitely look for another cause of the chain breaking before running it again.

aneway - I saw you PMd me but the pm said nothing

I am not getting my pms for some reason I get a notice but nothing in the mail box

If you have somthing to chat about email me at [email protected] :)

don't think the ignition issue had anything to do with the timing chain breaking...very weird, pull the engine down, either was some cheap chinese chain(does not matter if it was a brand name or not) or something wrong, ck dist and oil pump closely...Rob

+1 No way the ignition box could cause the chain to break.

Yeah, very weird situation for sure. I could easily see one or the other going out, but both seems odd.

Of course, turning a motor off at about 4300 rpm while still in gear can't be a very smooth shut down, and that's effectively what happened.

Hopefully we'll know more Friday.

Marc, I was replying about your truck that you had pinged me on.

I had the same thing happed to my boat @ 20 hr's of operation..turned out the aleignment pin came out of the front of the cam and got lodged between the chain and gears,blew the chain,blew the timing cover apart and bent all the valves..

just my o2

Bad Box?
 

Are you sure the original box was bad or was the lack of spark due to the distributor not spinning?

That was my first thought.

There are several grades of so called performance chains. I had about 100Hrs on the one that came with my rebuild kit. It had substantal chain stretch but had not broken. There is a reason why some cost $39 and others $159. When I did my Roller Cam upgrade I used a Rollmaster chain from RMbuilder. It was Billet steel with a pre-stretched chain. If a expert on this wants to chime in on this therory please do so. Good luck with your repairs.

Don't know, though piston compression would change ohm resistance at the spark plug, confusing the Box....You may want to ask MSD.

What procedure did you follow to diagnose the original ignition box "failure"?

Is it possible the procedure did not take into account a failure somewhere else, like the timing chain?

That's what I'm thinking. I would be willing to bet the original box is good. I would recheck it.
As for the chain, if I don't use a Jesel belt, then it gets a Rollmaster. I have NEVER had a problem with one...and I have used a ton of them. Good luck with it.
Eddie

Thanks to all on the well wishes!

Yes, the first thing we did was to retest the original box. No spark. (we had tried it on the other engine before ordering the new one as well) The MSD procedure is pretty straightforward. With the unit unplugged from the engine, you tap a jumper between two leads 5-6 times and it will fire. It you have good power and ground, this jumper test will result in a spark at the coil if the unit is good.

Old unit, no spark, new unit, sparks like a s.o.b. (using the MSD jumper test)


And as most folks predicted, it took out some valves and a guide to boot. No piston damage luckily. The guy doing the valve job noticed the non-bent valves wouldn't create a good seal with just vacuum, so he reseated them. They did fine with spring pressure, but not so much with vacuum. And the spring pressure was a little inconsistent as well. So, I'm going to replace the chain on the other side and pull the heads and have those valves reworked as well.

And I figure with the exhaust manifolds out of the way, the installation of the swim platform will be a snap! Trying to find SOMETHING positive here! :lolhit:

Ya gotta make the best of it. If not, you'll just cry.

The MSD procedure is pretty straightforward. You have the wiring harness disconnected from the motor, so the only thing it sees is power and the leads to the coil.

http://www.msdignition.com/page.aspx?id=3206

Just went thru this issue and below is something you should look out for....

Your engine builder may not have checked to make sure the timing gears were lined up... Also, camshaft run-out.... Both of these factors will contribute to your chain wearing out prematurely and/or breaking the chain and/or timing gear.

The one that I just did had numerous teeth missing from the cam sprocket. It turns out the cam sprocket was .020 further out than the crank spocket, which thankfully I was able to catch before failure!! My machine shop had to machine the back of the camshaft sprocket so I could get perfect alignment.. Then the end-play was at 40 thou so I had to adjust the timing cover to get that within spec as well.

Thus an FYI of what to look for.

Thanks Panther, we'll double check that