H34 Speed with Yanmar 3GM(F)

Steve Dion · Apr 6, 2009

Clean bottom, mixing elbow cleaning/replacement, proper prop.

If you decide to look at a new prop you should take a look at a Campbell Sailor Prop.

You want to be sure that everything is right with your engine before you start messing with everything else. Your engine should be able to reach 3500-3600 in neutral at the dock. I would be sure that you have a clean fuel system too. There is sometimes a screen on the fuel pickup that can block fuel flow. Be sure that all of your filters a clean (primary & secondary).

Has you boat been out of the water? I would assume that the bottom is clean if that is the case.

The mixing elbow is a job that you can do yourself. Remove it and be sure that it is not plugged with carbon.

seadaddler · Apr 7, 2009

More Info

Has it always been slow since you own the boat,my Hunter did the same thing and I found the Mixing Elbo to be the problem and once I cleaned it out it was like night and day.
It was spring and the bottom was cleaned also the prop was cleaned so it motored better than new.
The mixing elbo is a good place to start before you go crazy changing and spending $$$$$$.
Nick

Rick · Apr 7, 2009

Re: More Info

Dont know what year your 34 is, but you definately have an issue. If your only getting 3000 rpm underway and you can get 3400 in neutral its not your throttle linkage. You should be able to get hull speed or close (actually 7.33) at 3000 . Cruise rpm is 75% of WOT and although you can push the little yanmar at full throttle, you are just waisting fuel because your pushing water at that point. Does your exhaust have any color at 28-3000? Dark exhaust could explain a partially clogged mixing elbow or my theory, a bad prop. Your boat came stock with a 2 blader. The vibration you are getting is not normal on a three blader (bent shaft, bent blade). See if you can borrow a spare prop from a slip mate or I think there is even a 1 inch two blader for sale on this site cheap. This of course assumes the afore mentioned clean bottom, etc.

Cheers

Dan Johnson · Apr 7, 2009

ZDS...

On my '83 H34 (Yanmar 3GM30F) I regularly cruise at 2800 RPM which equates to 6 to 6.1 knots GPS SOG with no current. I may loose .2 knots by the end of the season, but a long days' motoring will usually clean up the bottom somewhat with the ablative bottom paint I use.

You definately have some issues--Steve hits the high points, but I've never gotten over 3400 RPM at the dock or under way with clean fuel/filters/new elbow/standard 2 blade prop, in or out of gear.

seadaddler · Apr 7, 2009

More Info

OK 3100 in neutral at the dock is not bad maybe tack is off a little but how about
when motoring do you put the hammer down to get full speed and does black smoke come out the exhaust when you put the hammer down trying to get more speed what is the max RPM's and if you are getting black smoke could be overloading due to coked up mixing elbo or fuel filters could be dirty.
Try the mixing elbo first than see what happens in motoring and than if no improvement try filters and see what happens,do one thing at at time to see what's the problem.
Nick

Steve Dion · Apr 7, 2009

ZDS:

Just because you have the "original" prop, does NOT indicate that it is the correct prop. This has been a complaint on many of the 2GM & 3GM motors. The prop from the factory was not necessarily the right one. If you take you prop to a shop they can check it for you and also run it through their computer to determine if it is the right size for your setup.

I do think that you need to elbow inspected. Be sure that you order a new gasket for the manifold before you remove the unit.

The best way I found to inspect the unit was to remove the bolts from the manifold and remove the entire unit from the boat. Quite often the exhaust hose is the worst part of the removal process. Once it is off the engine then you need to try to get the two units apart. This may be best to do with two very large pipe wrenches and breaker bars. It also helps to have a torch to heat up the elbow to get them apart.

If/when you get the elbow, coupling & manifold in three parts, you can determine if the elbow is worth cleaning or not. It is usually best to replace the elbow and coupling. The coupling has a left hand and a right hand thread (just be aware).

When you reassemble, be sure to use some never seize on the threads. It does not last forever but it helps.

petersea · Apr 7, 2009

zds,

OK to add my 2 cents here, you did not say where you are boating and if it is fresh or salt water. The elbow clog is a salt water issue just in case you are in fresh water. Just thought I would mention that.
If you are in salt water (or brackish) the elbow is the first place I would start also as the others have recommended. Next is the prop as others have also recommended.
The 3GM30 engine should get about 3600 rpm in neutral and 3400 in gear. The yanmar tachs are know for being less then accurate,give or take 100 rpm's so "interpret" you readings unless you have a tach gun you can hook up temporarily for accuracy. Your engine should idle somewhere around 750 to 850 rpm. (as reference info to see where your tach reads) If you do change the prop let me suggest you go to a three blade prop (unless you race). Your engine and a two blade prop will tend to vibrate and sound like a you stirred up a bee hive the faster the rpm's. You will be amazed the difference a three blade will make in smoothness , vibrations and noise. A good prop shop can hook you up with size and pitch.
As far as the heater loop yes I have had a boat with that engine (not the h34) and it will heat heat the domestic hot water as a matter of fact the water will get very hot ! I would guess you have a air lock in the lines somewhere near the heater if yours does not work. Mine had a air bleed both at the water heater and engine connection. Check there first. Mine also had a similar distance as you describe.

petersea · Apr 7, 2009

zds,

air bleed comes in different types but basically they are a drain valve. Look similar to the drain on you car radiator. Some are a petcock type like the water drains on your engine. some are similar to the drain valve in seacocks or plumbing valve that have a screw type cap to drain water. Simple check for a air lock is to feel the water hoses for temperature on a warm engine (NOT HOT) but you should be able to feel the water hose from the engine to the water heater and the return and they both should be warm to the touch. If one is warm and one is cold then you most likely have an air lock . Use caution as they should be very close to what ever the engine water temp is so a hot engine can be 150 degrees or hotter. trace your hoses and see if maybe someone put a shut off valve in line. As a general rule the engine water to domestic hot water exchange is a very good system and works well. Mount one in the lowest part of the hose loop and one in the highest part of the loop general just off the heater on the return side and one near where hose comes off engine. I will check to see if I can find any pictures but check in archives as I know this has been talked about in the past. Do the touch test first. If you install them when you go to bleed system with the engine running (cold or cool water temp) and the system full of antifreeze/water mixture open valve until any trapped air is released and only fluid comes out. This only usually needs to be done when changing antifreeze or if the system have been open to work on or maybe after a coolant leak that the level was low.
Another simple check to see if you are getting full throttle from the control handle is to disconnect the cable at the fuel pump and operate the fuel pump throttle level by hand and see if you get any higher rpm reading on the tach. Wide open throttle should be the same with the cable connected as disconnected.

petersea · Apr 7, 2009

zds

here is a link and a picture to give you the general idea. bleed valve in picture is on top of picture with the "t" type handle. most are installed in a "t" fitting with hose barbs on both ends not the best picture example but should give you a idea of what to look for.

http://www.thomasnet.com/cadlibrary.html?cov=NA&what=air+bleed+valve&heading=904

11000&searchpos=2&cid=10111455&az=74127424&navsec=products

http://www.generalairproducts.com/PDF2/General Air/drain valves/Drain Valve 4.pdf

DJ Sailor · Apr 8, 2009

Hunter 34s came with both 15x15 and 15x12 2 bladed, RH props. The early '83 H34s had Westerbeke engines while '84 and later came with Yanmar (mostly 22.5HP though some late H34s may have the 30HP model that Yanmar made). I had a 15x12 2-blade from the factory with my Yanmar 22.5 powered '84 H34 but switched with a 15x15 when a friend got rid of his. I've also used a 13" diameter 3-bladed prop for a while but got better calm weather performance with the 15x15 2-bladed prop.

I'd like to go with a 3 bladed 16" Auto Prop or Max Prop but 16" props probably do not have the clearance between the prop tip and the hull. Prop size also is dependent on how much weight your boat is dragging along. Throw out that old spare piece and check the exhaust mixing elbow. They really narrow down after 2-3 years.

Brad Hoff · Apr 10, 2009

I have the same engine and have hooked up a heat exchanger for heating the boat as well when motoring. I get enough heat to both heat the air and hot water system out of the 20hp Yanmar 3GMF. Hooked up the air heat exchanger just after the water heater loop. As previously stated, you need a bleed valve (same as the bleed/drain for an auto coolant system) at the highest point, which will be at the water heater.

For cleaning the mixing elbow, just soak overnight in muriatic acid. This will clean the carbon right down to shiny metal without any chipping, scrubbing, brushing, etc. It will not eat the metal but it does eat concrete so keep off of the driveway. I used straight acid from Home Depot. Works like a charm.

Brad Hoff · Apr 11, 2009

ZDS

I thought I had an engine photo but it doesn't show where the coolant lines exit. I will get a photo next week. I re plumbed the outlet off of the engine because I installed a larger Balmar alternator. The plumbing adds a tight bend which probablly increases the resistance. I was told that the addition of the air heat exchanger in line with the water heater might increase the resistance to the point of stopping the flow. I had some trouble initally because a very small amount was trapped. I was looking at installing a small 12v circulation pump but the air was finally blead and the system now works fine. Are you sure that all of the air is out of the line? I found that even a small amount of air will stop the flow. You may want to check the condition of your hoses. I replaced mine when I found that the water/oil in the bilge where the lines go through the lower pan to the water heater had eaten through the rubber. This was another issue where I was loosing coolant. Have you taken off the bi-pass lines and checked that they are free flowing and not kinked anywhere? The flow off of the bi-pass is not very strong in terms of overcoming resistance.

Fast Ed · Apr 11, 2009

I have a Hunter 34, and I have also never gotten the engine to rev above 3000 rpm's. My boat will motor at 6.5 KTs easily. I have a slipstream folding prop that is 16x10. My boat will motor at 6.5 kts. at 2400 rpms. When I bought the boat, the prop was too large. but would still push the boat at 6 kts.. I think you should consider a different prop, without knowing anything else about your boat.

Other replies suggest the mixing elbow could be at fault. I have had that problem, and it will cause you to overheat.

kloudie1 · Apr 11, 2009

H 34 Speed

ZDS.. here are the pictures I have of the water heater lines and heat exchanger lines. You can see the water heater lines running over teh alternator. In the other shot, you can see the sea water outlet going to the exhaust elbow. The original prop according to Hunter is a 15 X 15 two blade. I think it has too much pitch and results in the engine not being able to reach max RPM .. But it is great for fuel consumption.. about half gallon an hour at 5.5 kts. As others have said, get a good prop shop to look it over, but first, make sure the exhaust elbow is clean inside.

VINN · Apr 13, 2009

i can share some knowledge about this topic that may help you. my 84/h34 came with a 15x12 that peaked @ 3600 rpm. i thought the engine was over reving so i changed it to a 15x13. it peaked @ 3450. i really like this prop made by larry johnson of freeport ny. it has a little better bite, and the 5 knot speed limit breaths real good at 2100 rpm, and a 6 knots cruise at 3000 rpm. both props touched 7+knots wide open. yes, its really hard to get these little guys to spin smooth. after countless hours adjusting the mating of the couplings through that tiny access hatch, that nearly ruined my back, i can honestly say it finally reached harmony for almost the entire bandwidth, with a slight rough spot around 2850 rpm. thats caused by a 2 thousand of an inch difference between the left and right side of the coupling. ill need someone smaller and younger to do better than that. next to everything every one else said, it could be a # of allot of things causing your problem. do the easy things first. ck for good solid motor mounts, and make sure the bottom nuts didnt vibrate down the bolt. this will cause vibration for sure and limit revs. make sure the shaft is not rubbing on your stern tube, or is your stuffing box too tight. i replaced the entire drive train my second season, including the mixing elbow, cutless, and shaft and i still wasnt satisfied, until i got into that little access hatch and finished up all the dirty work. all this work has finally gone to naught for me when i moved to a new yacht club this summer. there are 2 soverel 33' and i might have to get a folding prop to make them honest. any suggestions? its going to be a very interesting summer.

H34 Speed with Yanmar 3GM(F)

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