Changing Timing Belt-Yanmar 300 Myself?

[Chris & Dale]

Maybe I've had too much success lately in doing some rather large projects myself, so now I'm actually entertaining the idea of changing the timing belt myself on our 1999 Yanmar 300 hp. I've heard talk of approximately $1000+ to do this job, so saving that is attractive, but I think what's more intriguing is that every time I take on one of these new projects I learn so much about this boat, and that's a good thing! Anyway, please share your experiences, pros and cons, and please be candid. This is one fantastic forum.

[efishnsea]

I have taken the course from Mack Boring on maintaining these engines. The words from my instructor were not to attempt this job myself. I could save elsewhere. Have the timing belt and valve adjustments done by the pros. Its not worth it if you have a problem.

[johnmurray]

I just had my timing belt changed by a qualified mechanic. He also changed the two drive belts and did a few other minor items. He did not adjust the valves as he said they did not need it. The job was tricky because access is very difficult and he had to remove and drain part of the engine coolant system before he could get at the timing belt cover. With this job it is critical that everything is properly aligned when re-assembled. He charged me for four hours work plus travel time. I thought that was very fair and I would not attempt the job myself.

[RobS]

I agree, unless you have mechanic background leave the timing belt (and tensioner) and valve adjustment to a good Yanmar guy, the valves can be the death of these 6lp's. With the tight access at the timing belt, the work is not staring you in the face, like being able to thrown something up on the bench... John, how did he know the valves did not need adjustment, by engine hours, by ear or did he put the gauge on them?

[johnmurray]

I didn't ask, but I think by hours (658) and a careful listen at various RPMs. He did not use a gauge.

[RobS]

I didn't ask, but I think by hours (658) and a careful listen at various RPMs. He did not use a gauge.

Yes, as long as the initial 250hr adjustment was done, it's not on the schedule until 1000hrs.

[halfmoon]

Is the need to change a Yanmar 300 timing belt a matter of engine hours or engine age.

[RobS]

Both

[Chris & Dale]

In our case, it's probably more age than anything. 13 years is a long time for anything mechanical to hold up. The book says 1200 hours for the timing belt and I'm not going to risk a catastrophic failure. There's no warning, hint, or any indicator...it just goes, and worst case scenario is a new motor at about $25,000. I've also listened to the collective wisdom here and from several big diesel owners who do a lot of their own work, and I'll have a pro do the job. Thanks Everyone for your input!