Mercruiser 165hp timing chain

[semo549]

Hey guys all this waiting around for spring to get here has got me doing some thinking. First off I have a 77' Searay with gm250ci L6. The boat runs good and it has for 2 seasons now but it doesn't run great. The problem is with the timing. When I hook my timing light up the reading dances all around on the harmonic balancer. The timing is supposed to be set at 6 degrees TDC. Well the reading I get bounces around anywhere from 3-10 degrees so it is impossible to set it accurately. I have always relied on adjusting it to where it runs the smoothest. The problem is that I have always had bad throttle response. from idle to a quick opening of the throttle results in a starving like hesitation.

Here are the things I have checked:
-Dwell is set accurately
-accelerator pump is squirting fuel properly
-I have installed new rotor, cap, plugs, wires, and rebuilt the carb 2 seasons ago
-I might be missing a few things...

so is this problem most likely a caused from slack in the timing chain? I found a timing chain and gear set online for a pretty good price. Should I be looking into something else? new distributor perhaps??? Any advise would be appreciated. Thanks

 

[semo549]

Re: Mercruiser 165hp timing chain

I forgot to mention that I have tried a few different timing lights so I know thats not the issue.

 

[fishrdan]

Re: Mercruiser 165hp timing chain

so is this problem most likely a caused from slack in the timing chain? I found a timing chain and gear set online for a pretty good price.

new distributor perhaps???

I doubt it's the timing chain, the 165HP L6 doesn't have a chain, timing gears only. The cam gear is fiber and can wear out, though my guess would be the distributor bushings. Remove the distribitor rotor and see if you can rock the shaft L>R F>B, there shouldn't be any noticable play. If there's play in the shaft/bushings, the timing will bounce all over the place.

 

[dan t.]

Re: Mercruiser 165hp timing chain

I would seriously wonder about the partsman that found you the timing chain set, being that the 250 L6 uses a gear to gear system with no chain. I would take a good look at the advance weights and springs, sounds like something is loose or worn out in the distributor

 

[Don S]

Re: Mercruiser 165hp timing chain

You can also check your dwell at different rpm, if the shaft/bushings are worn, the dwell will increase and decrease as you rev the engine.

You may also need to remove the points plate in the distributor and check the weights a springs for damage or rust.

 

[metalwizard]

Re: Mercruiser 165hp timing chain

I think I have the same issue (worn gears) is the front of your motor noisy when its running?

 

[semo549]

Re: Mercruiser 165hp timing chain

I would seriously wonder about the partsman that found you the timing chain set, being that the 250 L6 uses a gear to gear system with no chain. I would take a good look at the advance weights and springs, sounds like something is loose or worn out in the distributor

I found the gear set online, I knew it came with gears. I just assumed it came with a chain as well....

I think I have the same issue (worn gears) is the front of your motor noisy when its running?

I can remember if my engine was noisy, but I'm pretty sure it wasn't or else I think I would have noticed it. It runs and idles smooth.

I doubt it's the timing chain, the 165HP L6 doesn't have a chain, timing gears only. The cam gear is fiber and can wear out, though my guess would be the distributor bushings. Remove the distribitor rotor and see if you can rock the shaft L>R F>B, there shouldn't be any noticable play. If there's play in the shaft/bushings, the timing will bounce all over the place.

I will try this on Friday and get back to you. If there is worn distributor bushings should I be looking at purchasing a new distributor? I found one from summit for under $200. I also found the timing gear set from them too for $70. Should I be looking at picking those up as well? I like to think I know alot about engines but the whole ingition system is slightly new to me. Thanks for the replies

 

[semo549]

Re: Mercruiser 165hp timing chain

I just found this video on youtube on how to install a new distributor. Does this look like what I have to do? Because this looks fairly simple.

The video is only 2:30minutes, Sorry I can't figure out how to embed the video.
http://www.youtube.com/watch?v=YdIGZ-tVuZA&feature=relmfu

 

[Silvertip]

Re: Mercruiser 165hp timing chain

I just found this video on youtube on how to install a new distributor. Does this look like what I have to do? Because this looks fairly simple.

The video is only 2:30minutes, Sorry I can't figure out how to embed the video.
http://www.youtube.com/watch?v=YdIGZ-tVuZA&feature=relmfu

Until you diagnose the problem you "don't" know if this is what you need to do. Don't start throwing parts at the problem as this is an expensive way to troubleshoot a problem.

 

[fishrdan]

Re: Mercruiser 165hp timing chain

^^^ agree with ST, don't go throwing parts at it, diagnose first.

The timing gears can be a real PITA to replace, they are both pressed on. When I rebuilt my 140 I tried to remove the gears, after fighting it awhile I said to *ell with it, let the machine shop press them on/off while they do the rest of their work. I doubt you will get the timing gears replaced with a hydraulic press, and the cam/crank out of the engine.

Is the Summit distributor a "marine" distributor? It needs to be "marine" or you boat could go BOOOM!

BTW, those 35+ year old gears in my engine were still fine, fiber gear was still in good condition.

 

[brntrt]

Re: Mercruiser 165hp timing chain

Het semo, I used to work on those engines for a living some years back. I was a cert. merc. mech. and those ole 250 ci were a work horse! My bet is all your trouble is in the distributor. We would pull the Dist. with every tune up we did, and check the bushings on the main shaft, and pull the breaker plate and check the all the fly weights and springs as well. We had a dist scope and we would check the advance curve as well. With the marine engine not having any kind of vacuum advance it was very important that the dist worked correctly. Also make sure if you do replace the dist. that you use the marine version as stated earlier, not only for the BOOM factor, but also for the advance curve. I hope this helps. Good luck

 

[Fishermark]

Re: Mercruiser 165hp timing chain

I also found the timing gear set from them too for $70. Should I be looking at picking those up as well?

You don't need to buy a gear set. Those gears work until they quit. They don't wear out and get sloppy. The fiber gear can break, but that's about it. You may even have a metal gear not the fiber one. Here's what mine looks like so you can see them in place:

 

[semo549]

Re: Mercruiser 165hp timing chain

Thanks again for the help everyone. Looks like i'm in the market for a new distributor. Would using a distributor from an engine out of a scrap yard be worth trying out and just swap over the newer cap, points, rotor etc...? I know a guy at the local marina that has a few 165's laying around, I got a manifold from him for cheap this past spring. Seems the marine distributors for this engine is hard to find these days. Anyone know a place I can get one from that doesn't cost $600?

 

[brntrt]

Re: Mercruiser 165hp timing chain

Thanks again for the help everyone. Looks like i'm in the market for a new distributor. Would using a distributor from an engine out of a scrap yard be worth trying out and just swap over the newer cap, points, rotor etc...? I know a guy at the local marina that has a few 165's laying around, I got a manifold from him for cheap this past spring. Seems the marine distributors for this engine is hard to find these days. Anyone know a place I can get one from that doesn't cost $600?

Hey Semo, price out a sierra 18-5487, this is a complete replacement with electronic componets.

 

[fishrdan]

Re: Mercruiser 165hp timing chain

Would using a distributor from an engine out of a scrap yard be worth trying out and just swap over the newer cap, points, rotor etc...?

Unless it's from a boat engine, no. It needs to be marine.

Automotive distributors are not ignition protected (explosion proof), they have a vaccumm advance that's not used in marine applications and the advance curve will be wrong.

Will it fit and will the engie run with an automotive distributor, yeah, but the engine won't be at it's full potential and it's risky.

Sometimes you have to pay the piper.

Here's a thought (don't know if it will work,, but) Pertronix makes an electronic conversion for that distributor and it might work with the slop in the shaft bushings, might not too. It would be worth a call to Pertronix and ask if shaft play will cause a problem, or if there is a service limit where the electronic conversion will work. Basically, the electronic part replaces the points so you don't have to worry about adjusting the dwell. This is a band-aid fix and won't solve the loose bushings, but it might get the ignition stable.

You could also check out Ebay for a used distributor, but you could be buying another bad distributor....

 

[semo549]

Re: Mercruiser 165hp timing chain

Hey I know this is an old thread but I finally got the probem fixed so I figured I'd share the results. I went ahead and bought a set of advance weight springs for the distributor. I inspected the old springs and could see gaps within the coils. The new springs actually have a good amount of tension to them. Got her fired up and the timing is holding solid right where it should be. I'm pretty pumped about it. Boat ran better than it ever has this past saturday. It also raised my WOT up 500 rpm's. With a full load of gear and 4 adults with a 17p prop I used to turn 4000rpms. On saturday with the same setup I spun 4500rpms. WOT for my engine is 3900-4300 so I'll be putting my 19p on next time I go out.

Got her all cleaned up for the season too. Just acid washed below the waterline and turned the hull bright white again. Here's some pics from saturday.

 

[Don S]

Re: Mercruiser 165hp timing chain

After changing the springs, did you check your advance to make sure it works correctly and give you the proper advance?

 

[semo549]

Re: Mercruiser 165hp timing chain

All I did was set the timing and dwell at idle. I just assumed it would be correct considering it was an oem mercruiser part. How would I go about checking the advance curve? Just rev the engine with the timing light hooked up and check the reading?

 

[Don S]

Re: Mercruiser 165hp timing chain

I just assumed it would be correct considering it was an oem mercruiser part.

Not sure how you found the OEM parts, they have been listed as NLA (No Longer Available) for years.
I would hope you know what assume stands for.

Anyway, yes, you can use an advance timing light to check the advance timing with an accurate shop tach to check the advance at different rpm.

 

[Pete104]

Re: Mercruiser 165hp timing chain

Great info on an old unit. Thanks for the updates.

You must be pretty far from the storm that came thru Joplin! What a tragedy!