OT...V6 Chevy marine engine distributor gear trouble

[Jr ///M5]

A good friend of mine is having trouble with his V6 marine engine for his boat. He bought the engine about 6 years ago and finally installed it (short block) After about 20 minutes in the water the thing died flat. He towed it home and started checking spark, fuel, and air. He brought over the distributor and showed it to me, the distributor gear was knife edged and sharp to the touch. He decided to replace the gear and give it another go. Same thing happened.

I told him to check the end play in the distributor and make sure it wasn't binding against the oil pump. He assured me he had and there was approximately 30 thousands of shaft clearance vertically. He dyed the new gear with machinists dye and ran the motor again for about 10 minutes. Then pulled the distributor again to find the same thing happening again to the gear. The next thing I told him to check was flexing of the timing chain cover and replace it with a stiffer unit along with a cam button to insure there wouldn't be any cam walk.

If this doesn't work, I don't know what else to try. He's at wits end with this thing and almost ready to buy another block. This rebuilt engine is a Jasper engine for what it's worth, I'm not familiar with this company or V-6 Chevy engines for that matter. Any direction or idea of what to consider next would be appreciated.

Thanks for the bandwidth,
JR

[Dr. evil]

sometimes if the cam is an aftermarket unit they can be case harded and require a special stronger gear.

is he using brass gears?

[indierthanthou]

merc 4.3 LX?

[attack eagle]

Jasper is VERY reputable IIRC.

[Jon K]

JR, I don't know how inclined he is, but you can ditch the distributor all together and run a DIS on that motor fairly easily :)

[Jr ///M5]

It's not a brass gear, it's ductile iron. The cam is probably an aftermarket due to the engine needing low end torque. He changed the cam with the other engine just in case the first one was damaged. There wasn't any change, the gear still knife edged.

The dye showed the wear as if the cam was being forced to the rear of the engine. The top 1/4" portion of the distributor gear wasn't making any contact with the cam gear at all.

There are several causes for this type of gear wear. Using the wrong type of material for the distributor gear is one. Using high volume oil pumps is another. Axial clearance through the distributor, and finally, cam walk. Unless there is something wrong with the rear camshaft bearing?

I finally told him to replace the timing chain cover with the stiffer unit and use a cam button, but it sounds like a harder gear is also necessary. It's not a matter of $, he's an orthodontist and could afford a new boat if he wanted. It's more of a matter of finding the solution for the problem rather than throw big $ at it. Besides, it's more fun....anything else you guys suggest? Thanks for the ideas.

[Ferret]

If the back end camshaft bearing is knackered, is it forcing the gears to mesh up the front end too hard?

Do the gears have the right clearance and the exact same pitch?

[winfred]

still needs a oil pump drive which could get chewed up in the same way


JR, I don't know how inclined he is, but you can ditch the distributor all together and run a DIS on that motor fairly easily :)

[Ross]

Seems as if the cam is being driven back with some considerable force. A helical timing set would have been my first guess but since you mention a chain that's out. A cam button will keep it from walking forward but you say it's being driven back.
Misalignment between the line bore for the crank and the cam bore would do it. I've never seen it though. Does the timing set show signs of misalignment?
If this motor had previously been allright then my theory blows. If it is new or freshly remachined then maybe poor machining is the cause.

[632 Regal]

if its a high volume/high pressure oil pump with a thick oil, thats the problem. Either run a thinner oil like 5w-40 mobil one or replace the pump with a stock type pump. In boat motors the oil never really gets hot because of the way they are cooled so the oil never thins out and the pump is working VERY hard to circulate that thick stuff.

[Jr ///M5]

if its a high volume/high pressure oil pump with a thick oil, thats the problem. Either run a thinner oil like 5w-40 mobil one or replace the pump with a stock type pump. In boat motors the oil never really gets hot because of the way they are cooled so the oil never thins out and the pump is working VERY hard to circulate that thick stuff.


You might have something here Jeff. Normally, Chevy engines are noted for the top end oiling. With relatively low rpm, and coupled with the fact that the oil never gets warm enough to flow freely around this part of the engine could be a contributing factor. I have seen where the last journal of the distributor is supposed to be filed with a triangular file to allow the oil to drain down from the valley area in when at low RPM.

I have no experience with marine engines whatsoever. But it makes sense that they have to make power down low. The engine goes from idle to full throttle upon takeoff and the cam is ground to work at low rpms. There's some kind of clearance problem. I think the cam is walking back under engine torque.

A couple weeks ago I asked him to call Jasper to verify that they do not use high volume oil pumps. They said they didn't...but it didn't occur to me to ask him what weight oil he's using...

[632 Regal]

i dont think cam walk is a problem, the distributer gear doesn't care where the cam is unless its going too far and only running on the edge of the teeth. Also sounds like the wrong cam for the application but thats a story for another day after figuring this problem out.