Talk:Changing Engine Mounts

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Comments & perspectives from the Message Board

I used a 4X4 across the companionway and a chain hoist to lift the engine, other than that I used the same procedure. One other thing, if you don't already have a hose attached to the drain plug for pumping out oil, this is an excellent time to install one. Cap'n Stan

Have a few comments: I tried the 3" spreader jaws first. The deck Liner under a C34 is curved and after trying 1"& 2" lumber combinations and having the engine SLIP off the jaws 3 or 4 times I discarded that method. Wasn't to sure how strong the liner is anyway. It may work on a C30, but wouldn't recommend it for a C34. I thought of using a 4X4, but discarded that way of lifting, as I used what I had on the boat (a chain hoist will work) and was worried about screwing up the teak on the top side with a 4x4 sitting on two other pieces of 4x4s( to stand off from to teak strips). A few thoughts. Ron Hill, APACHE #788

Allow me to jump in here on this topic. I have used NorShipCo out of Norfolk, Virginia for the Universal brand of mounts as found on the M-25/M-25XP diesel engines installed in the Catalina 30. They are factory engine mounts, pricey, but exactly what is required. On several occasions I have replaced these mounts using a hydraulic jack to raise the engine. This particular jack is found used in automotive body shops and has various attachment devices. The device I use is a 3" spreader jaw. It is necessary to remove a good portion of the shelving directly above the rear of the engine for clearance. For course you will disconnect the prop shaft. Carefully measure and record the height of each engine-mounting bracket from the engine-mounting rail. This dimension is later used to rough in the engine alignment.

I place a "6 by" piece of wood on the bilge floor under the front of the engine and continue stacking wood blocks until the spreader jaws barely slip between the last piece of wood and the oil pan. Loosen and remove the front engine mount locking nuts. Remove the four lag bolts securing the front engine mounts from the rails. Loosen and remove the rear engine mount locking nuts. For stability when raising the engine, DO NOT remove the four lag bolts securing the rear engine mounts from the rails. After that, it's a simple matter to raise the engine and replace the front mounts. Bolt the front mounts to the rails, lower the engine, and do not replace the locking nuts. Repeat the entire process for the rear mounts. Liberally application a silicon sealer to the engine mount lag bolts to prevent water from penetrating into the wooden rails. Align the engine. Connect the prop shaft coupling. Done. Takes two hours. Joe

Vetus offers a mount called "MITSTEVN" and claim that the difference in vibration is "truly staggering." It's good for engines up to 35HP. Anyone have experience with it? Also the PYI Flex coupling claims to handle up to .010 runout. My mind isn't able to calculate how that compares to the 2 deg. that VETUS handles. The VETUS looks nice on the APACHE and I know you swear by it Ron but I'm wondering if anyone has the PYI in operation. I looked at the PYI at the Miami Boat Show and although it looks simple, I didn't see much flex built into it, (I met Joe & Pat Turner also, bought some packing and had a nice chat). I would think that with less vibration being transmitted to the boat via better isolation mounts, more stress is being put on the drivetrain. Has the solid coupling ever failed due to fatigue? Does the cutlass bearing ware more or less? Anyhow, I'm changing the mounts and I'm leaning to the MITSTEVN because of the "simply staggering" remark, I'm reluctant to be the first one though. Ron Kash, Rondevou # 315

You must consider the trade-off between flexibility and movement. Don't use bearings that are too soft. Soft bearings allow the engine to move without applying, as much force to the engine beds, and therefore the hull, but the cost is movement. Less force to the hull means less vibration; hence less noise. But unduly soft bearings would allow too much up and down movement at the shaft causing the shaft to hit the shaft tube, regardless of the coupling flexibility. Remember that the shaft clearance in the tube is only about 1/8 inch even if you've properly centered the shaft. Undue flexibility in the fore-aft direction will also cause another problem; propeller thrust is passed through the transmission into the engine and to the hull via the engine mounts. At full power that thrust is maybe 600 to 700 lbf. If the bearings can deflect foreword too much the whole engine, shaft and propeller will move forward. If you look at the shaft at the cutlass bearing you might already see some signs of movement. Further if the bearings are too soft vertically the engine can pitch up at the back and down at the front due to the propeller thrust causing rotation and lifting at the coupling. So, don't get carried away with installation of soft mounts.

My thrust calculation is approximate, based on ((2/3) x 20 [hp] x 550 [ft-lbf/s]) / (7 [nm/hr] x 6076 [ft/nm] x (1/3600) [hr/s]) = 620 lbf, where 2/3 is an assumed efficiency of power conversion to thrust. My apologies to engineers who have better knowledge of efficiency and to non-engineers for complicating matters with calculations. Probably the best installation would be to carry the propeller thrust to the hull at a bearing on the shaft with a double universal joint between the thrust bearing and the engine and then use very soft engine mounts. The engine mounts would then only have to prevent the engine moving too much as the boat pitched when sailing. And that system is on the market; they advertise in most sailing magazines. However, we don't have the space to install that type of system. If we could we'd have as quiet an installation as one gets with an onboard genet. In case you weren't aware, many engines are actually based on the same Kobota engine that's used for the 25XP.

I've recently added the R&D bearings (part 800-033) and had previously installed their flexible coupling; both sold by PYI in USA and Canada. I'm very pleased with the result. Now I'm into adding sound absorption material behind the engine and in the head cupboard. I actually went to R&D's factory north of London to get the mounts. The owner recommended those mounts as opposed to others he makes based on experience and testing. He reported experimenting with the Kobota engine that forms the core of the Universal 25XP to improve its vibration characteristics, finding it could be improved significantly by adding a much heavier flywheel. Unfortunately, that's not a practical proposition for us and the extra weight could overload the crankshaft or its aft bearing, thereby reducing their life expectancy.

From a practical perceptive, you'll find your choice mounts are limited by the space on the engine bed and the clearance between the bed and the engine. On my 1988 C34 with a 25XP it's hard to fit other than a mount with 4-inch bolt-hole centers because there simply isn't enough space on the bed to install a 5-inch mount. And the vertical clearance of, I think, about 2.75" precluded many taller mounts. Charles Holder, C34 #617

A typical boat maintenance weekend I fear:

Task: install new Vetus motor mounts. The vibrations at certain RPMs finally got to me. M35A in a '91 C34. Ron Hills notes on the C34 web site are very good on this by the way.

Changed out the front mounts with no problem. Rear mounts: the old boom vang I tried to use to hoist the engine. Just didn’t have enough purchase (bad planning on my part). The $15 come-a-long sitting in the garage will remedy that next time.

Noticed some black exhaust smoke on the insulation where the exhaust pipe screws into the exhaust manifold. The exhaust pipe is loose enough that I could move it by hand. Will have to disassemble and see if it just needs tightening or if the threads are burned up. Anyone have any experience in this area? Any recommendations? It seems from reading the list the exhaust pipes are SS after certain years? A good time to install the hump hose I assume.

The starboard rear mount looks relatively easy. The port one ?? Not sure I am enough of a contortionist at my age to change that one. Re-aligned the shaft. More background: the last couple of times out the engine idle was a little rough and when in gear would drop down to 5-600 rpm but still ran OK.

The problem: after getting everything back together and starting the engine, when the rpms drop below 1000, the engine shakes really bad and seems to surge intermittently. At 1000 and above it smoothes right out. The shake is there with the transmission in neutral. Just gets worse when in gear. With the transmission in gear, the engine is silky smooth above 1000 rpm all the way to 2600 rpm, all the bad vibrations in certain rpm ranges are gone and this with only the front 2 mounts changed.

I can't figure out how changing the front mounts could have caused the engine to shake like it does at low rpms. If it did, anyone have any recommendations on the fix? Could having the new mounts in front, the old in the rear be the problem?

Also, the engine manual doesn't list an idle speed rpm. It idles normally at about 800. Is this about normal for the M35A? The manual says to not mess with the throttle linkage stops under penalty of death. Anyone know how to adjust the idle without moving the idle stop set screw? Although 1000 rpm is a bit fast I think.

Hope this makes sense, as I am a bit confused about the whole situation at the moment. Any suggestions appreciated. Also, has anyone considered cutting out an access "door" in the rear birth so you can align the shaft, access the heat exchanger, etc. if your not a 13 year old gymnast? It is my understanding the Mark IIs has one?

Jack Mansfield, #1169 High Cotton II, Port Arkansas, TX

WOW! I had the same results with the vibration at slow speed after changing my mount last week. Here is a note I sent to Ron Hill and his reply. Hope it helps.

I did my engine mount switch over the weekend and then motored 9 hrs total the next three days. Yes, it is quieter but when I stopped after the first day the low idle would shake the engine where I thought it was going to rattle out of the boat. Sped it up to 900 rpm, where it should be anyway and it goes away. So I went below on a fellow C30’s boat and tried shaking his engine and it would NOT MOVE at all. Went back to mine with the new mounts and I can shake it all over the place! If it shacks side to side will it not shack front to rear? It does show how it keeps the vibration reaching the boat but they seem very soft to me! It is much quieter when running and I have tried twice to align the shaft with some success, but it seems hard as the feet need to be preloaded and as I adjust one it throws off another. I do have to remove one (someday) and make the slots wide for more sideways movement. All in all I like them but being able to shake the engine by hand bothers me a little.

Thanks for any comments.

Capt Al, "Kindred Spirit" #55


Al: Let me see if I can adequately answer you questions on the Vetus K50 mounts. Vibration. I learned in a Diesel Mechanics Course that a diesel engine inherently vibrates side to side. I placed an indelible mark on the drive shaft just forward of the packing gland nut and I haven't seen the mark move or signs of rubbing out. At haul out I saw no shinny spots on either side of the drive shaft at the cutlass bearing. So I don't think the shaft is moving any distance fore and aft - to speak of. When I asked what RPM the diesel should idle at the answer was, "just above where it doesn't shake your teeth out!" The course also demonstrated that at a higher rpm than idle, an engine (less the gyroscopic precession from the "spinning of the flywheel") would sit in one place while running! If you think about it, everything inside an engine is highly machined & must be well balanced or the seals would go and it would self-destruct from the inside. I've found that my high output alternator will not really start putting out amps until you hit 1300 -1500 rpm. Also, when it's putting out 60+amps the side load is about 3hp drag down, so you need to keep the rpm above a low idle. My engine shakes at 800rpm, but I don't idle the engine much below 1200 anyway, because at low idle is where the engine also loads up and carbon accumulates in the top of the cylinders. Going into a slip I'll go into lower idle (9-1000), but the shifter will be in neutral and not for too long. Shifting at a low rpm is hard on the engine (Especially with boat moving forward when going into reverse) and shifting at 1500rpm & up is hard on the transmission.

Alignment. I was able to get mine within .001" and did recheck it a couple of times. I did not run the engine in-between, because I didn't think of doing it. I just wanted to make sure it was correct before I took off the hard coupling and reinstalled my flexible coupling. That was a little bit of a pain to do.

Have to admit I've never tried to shake my engine. I did ask Vetus what the life of the mounts were and the reply was, "if the engine is properly aligned, the mounts will last the life of the engine." The problem with our Universal engines is the location of the oil filter above the FWD port mount and the Oberdorfer/Sherwood weep hole just above the FWD starboard mount. If you happen to have an oil leak in the engine side of the raw water pump or spill some oil changing filters, that oil will KILL the rubber in any mount.

Think I may go the boat tomorrow and I'll try to shake my engine. Since installing the new K50's I think I've put on 400-500 hrs (1-1/2 seasons). Having motored a total of 3500hrs +, you couldn't give me the old style mounts back for free - installed!!

Hope I've made some sense. Let me know if I've cleared things up.

Ron Hill

I was able to reach the front mounting bolts of the REAR mounts from the front of the engine. Then I crawled into that hole in the aft cabin and removed the back bolt and the foot from the engine. Just a comment to help if you want. I found that if I put the metal cover part of the new foot in a vice that I could undo the lock nut that holds the foot threaded shaft and remove the shaft. I now had a foot with no threaded post. Now you can put the foot base on first and pass the threaded post down thru the engine and screw it in with the appropriate nuts and washers and never have to lift the engine. So you ask how did I get the old ones out without raising the engine? I used my saw zal with a metal cutting blade and cut the shaft right above the old foot base. Before I started I measured the height of each corner of the engine. Then I started with the front right and cut out the old and put in the new, adjusted its height and then moved on to the next. I only worked up a sweat on one of the rear feet because of working on my head. Sorry if this sounds too easy for those who have do it the other way but the new feet DO come apart. Be very careful when tightening that lock nut on the shaft to base as it will turn the metal cover. Make sure everything is straight before tightening the adjusting nuts to the engine.

Capt Al

Capt. Al, thanks for the response. Apparently this not an uncommon event when changing to softer mounts. Will change out the rear mounts next trip down and see what that does. May just have to idle at 1000 with the new mounts. Having the engine run so smoothly otherwise will be a good trade-off. As Ron said, will just have to spend more time in neutral when docking to Keep boat speed down. I didn't have any problems aligning the shaft (other than it's a b&%# to access the coupling). Perhaps the heavier weight of the M35 makes a difference there??

Jack Mansfield, #1169, Port Aransas, TX

Capt Al,

Just a quick question about why the higher idle. Most of the Yanmar/Universal engine books recommend 8-900 idle to minimize the noise and more importantly the additional wear on the transmission shifting gears.


Randy, SO WHY THE HIGHER IDLE???? Because the engine shakes at 7-800rpm with the new mounts. The shifting seems fine at 950 RPM; I do not worry about that. Also you have to be able to hear the engine and at 700 rpm and with the new mounts it’s "quite"......if it does not shake. THE ENGINE IS MUCH QUIETER AT ALL SPEEDS WITH THE NEW MOUNTS!

Capt Al


For a bit more background, C34s seem to have an inherent design problem with engine vibrations at certain rpm ranges. In particular all the woodwork around the engine compartment, cockpit locker doors, etc really set up a loud, irritating harmonic vibration. You just don't run in certain RPM ranges (1500-1700 rpms were the worst on my '91). The factory engine mounts are very hard, almost no give. The Vetus are "softer" and absorb the vibrations rather than transferring them to the stringers. The downside seems to be having to run at a higher idle speed. As Al said, the engine is MUCH quiter at all speeds above 1000 rpm, a very good trade off as far as I am concerned. Perhaps they have changed things on the Mark IIs? Jack Mansfield, C34 # 1169, Port Aransas, TX

Not being happy with what I initially thought of as "slight vibrations" when cruising, I purchased a set of K-50 motor mounts from VITUS as suggested by Ron Hill. As per Ron's advice, I filed the slots of all four mounts in the lateral and fore and aft directions to facilitate alignment of the engine. By using my 3-foot homemade side bumper plate (actually two 2"x4"s screwed together with rubber feet mounted at each end) laid across the top of my companionway, and a come-a-long connected between a homemade engine harness and the bumper plate, made the job of raising the engine real simple, that is, once I removed the lock nuts on the old mounts and disconnected the drive shaft. After epoxying all the old lag screw holes, the installation of the new K-50's was easy. Alignment of the engine took a little time but went well. Yes my engine is now easy to shake, not so much fore and aft, but from side to side. Now, as many others have experienced, testing out ! the new K-50's came with all kinds of new and greater vibrations. (Ask Ron, he felt them too). To make a long story short, what the old stiff motor mounts hid, the new flexible motor mounts exposed. My vibrations were not caused by the motor mounts, but by the engine itself. I pulled my injectors only to find that all three were badly varnished to the point where one would barely open and another had a broken spring. Also, I checked my valve lash and found that my No. 3 cylinder valves were out of adjustment. Another thing that I found is that the water muffler foundation separated from the the hull. You can almost guess what my floating condominium sounded like when I took her on a test cruise with the new K-50's (not to mention how much I wanted to strangle Ron Hill for bringing these K-50's into my life). Even my eye teeth shook. However, after installing rebuilt injectors, adjusting all valves properly, re-glassing the muffler foundation to the hull, and rechecking the engine alignment, I too would not trade my new K-50's for any other mounts.

Hank Recla, #954 "Bay-Tripper"

I made a "shroud " to place over the fwd port engine mount, so oil from a filter change cannot get on my new mount and "eat" up the rubber. I used a Zip-lock disposable 1 cup container. They come in packs of 6 for $2+? I drilled a 5/8" hole in the top - off center. With a utility knife I made a cut from the hole down the "short" side. That cut allowed me to slip it around the mount with the cut facing aft. Then I sealed the bottom and "cut" with some masking tape. Used a rolled up paper towel around the top and a wad just under the filter. Loosen the filter until you can turn it with your fingers. Drill a hole in the top on a ridge and mark the hole position on the "top" of the filter. Place an old coffee can under the filter. Turn the filter until the hole is on the bottom and draining. To speed up the draining drill another hole in the top of the filter. When it stops draining, spin off the filter and let it fall into the can. Place the old paper towels and those used for any clean up in the can; secure the lid and properly dispose of the whole thing.

Ron Hill