J/30 Class Association Forums J/30 Forum The Boat, Sails and Equipment Engine mounts

I'm in the final stages of purchasing an '82/400-series J/30. Only thing left is the survey. During the sea trial, the engine vibration when engine just above idle was quite harsh. I've been told this is normal for that vintage of boat (I've mostly sailed newer J/30s - 1984 with the newer layout) and actually better than most because this boat recently had strut, shaft, and martec replaced.

So - I'm curious about a couple things:

- is this consistent similarly aged J/30s?
- I was told the newer J/30s had refined the engine mounts; has anyone tried to retro fit an older 30 with a newer style mount?

Would be great to get rid of that vibration... Any suggestions or experience would be much appreciated.

thanks,
- JBro

311 is an 81 with new mounts and at tickover the thumps raise the coachroof & you can watch the winches dance and your vision is blurry if you are properly barefoot. It would be interesting to see the two different J/30's you refer to. You might have the best persepctive on it. Engine mounts can be replaced. They are mounted on big glass stringers, and that may be the point of improvement across model years.

I have an 82 #397 and the motor is a bit loud but I do not have any vibration issues. My guess is that although mounts wear out, if there is nothing causing the vibration they will still not vibrate too much. You need to isolate the cause of the vibration.

I would have the prop reconditioned, replace the cutless bearing, and have the shaft checked for being true and then have it aligned by a professional. I had this done last year and I could not belive how smooth the boat ran.

I would also check that your pullies for water pump, altenator etc are not out of round and that all the belts are tight. A loose belt can cause a lot of vibration.

It will never be really quite but it should be smooth with no large vibrations moving the winches around (-:

David
#397

Thanks - appreciate the info. Actually, the prop, shaft, strut and cutlass bearing are all new and were installed professionally less than a year ago. So, the tip on the belts and pullies is a very good one. I'll need to check those. I did notice one of the belts was looser than I would have it while I was inspecting the boat.

My feeling too is that it shouldn't be terribly rough unless there is something worn or structurally questionable in the mounts.

Thanks for the info folks - much appreciated.
- JBro

[This message has been edited by JBro (edited 04-29-2007).]

Appreciate the additional input. When we are idling, this is when the little 2 cylinder thumps. When we increase RPM's even slightly it all smooths out. It's very smooth underway. Sometimes if we need to idle for a while, we'll just increase R's to smooth it out. It idles easily but adding a touch of throttle smooths it out. Hm, belts. I've checked them annually. I'll check 'em again ! Thanks.

I have same symptoms when my 2GM is at idle and attribute it to normal operation of the engine. I just rebuilt my Yanmar and notice lots of vibration at idle (same as before rebuild). It smoothes out as RPM is increased, and is noticiebly smoother now the engine is rebuilt. If you have similar response, I think it is "normal".

I agree, at idle they are pretty rough. But underway they are very smooth.

David
#397

Most diesel engines do not like to sit at low idle for long periods of time. I think it has something to do with carbon buildup. If you are going to idle for more than a couple of minutes, you probably should bump up the idle anyway.

Thanks everyone - this really helps. It's certainly reassuring to know that this seems to be a "normal" thing on these boats. We'll still analyze the oil, check belts, etc. but at least this isn't a unique experience.

thanks again!
-JBro

You might try increasing the idle speed slightly. To adjust mine, I increase idle speed until it is really smooth, then decrease until it starts to shake too much, then increase just a little from there so it just stops really shaking. Don't want idle so high as to make shifting into gear too abrupt.
Also, I have not done this yet, but I think poorly adjusted valves and/or dirty/worn injectors can effect idle.

[This message has been edited by alcal1750 (edited 05-01-2007).]