Thought this might be of interest to someone. Recently, when I had the engine (M25 Universal) in our 86 E32-3 hoisted up (I built a nifty hoisting jig out of 2 X 4s and turnbuckles) to remove my transmission for rebuild I also replaced the Motor Mounts. I chose “Thermoboat” brand which the Seattle Boat Show sales force said were engineered to reduce engine vibration transmission into the boat hull. Sounded good. Although not convinced of just how much reduction of vibration I would realize I installed the 3 recommended drop in replacement “Poly Flex Mounts”. I am very pleased to report that almost all of the engine vibration I used to feel in the cockpit is now gone! Where before, certain engine rpms would rattle this or that, basically now nothing rattles at any rpm and it just feels smoother. I can run at any rpm I choose and it is very smooth. Yes, I can still feel a little engine vibration but I never expected it to be totally smooth. I am happy I did this job. I ended up purchasing the mounts from “The Prop Shop” in Mukilteo, WA (800-634-8318) and they set me back about $100 each. This combined with the 3 blade prop install I did a while back has given me a very smooth motoring boat. I prefer sailing but the wind just isn’t always doing what I want. Spring and summer are coming, yeah.
Motor Mounts Reduce Vibration?-Yep
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Kim Schoedel
Member III
Thanks for the post. We have the M25 as well and in fact had the local guru's check the alignment last fall since at certain RPMS we have vibration. I have been told from other owners that "some" vibration is normal with the 3 cyl Universal, however, I still think there is more than I like. The Guru wants to go out for a spin when the weather breaks to see what's up.
BTW, the alignment helped a bit but still get some vibration over 2000 r's.
BTW, the alignment helped a bit but still get some vibration over 2000 r's.
Kim,
A couple of things come to mind. If you have a fixed pitch 2 blade prop there will be what I call "blade thumping" which the engine has nothing to do with. That was the first thing I changed on our boat and installed a 3 blade sailor. Very significant difference. Then of course I could feel the engine induced piston firing vibration a lot more. And I wanted that reduced too. I too had an engine "guru" check the engine and he verified that each cylinder was firing about equal and that is sounded and felt "normal". Well "normal" meant that they do vibrate, more at certain rpms and excite boat structures into resonance. Hence rattles and perceived vibration. But I felt these resonances more at slower rpms and operation above 2000 was fairly smooth. That makes me wonder about yours vibrating more above 2000. Almost sounds like something out of balance or not firing equally or something? Oh, are you propped for 3000 rpm at full bore operation? That is important to not lug the engine and it keeps things a little smoother. Other than that, unless you have a broken or bad motor mount I don't think the fancy mounts I installed are the answer to your particular problem. They would help of course. Will be interesting to hear what your "guru" finds.
A couple of things come to mind. If you have a fixed pitch 2 blade prop there will be what I call "blade thumping" which the engine has nothing to do with. That was the first thing I changed on our boat and installed a 3 blade sailor. Very significant difference. Then of course I could feel the engine induced piston firing vibration a lot more. And I wanted that reduced too. I too had an engine "guru" check the engine and he verified that each cylinder was firing about equal and that is sounded and felt "normal". Well "normal" meant that they do vibrate, more at certain rpms and excite boat structures into resonance. Hence rattles and perceived vibration. But I felt these resonances more at slower rpms and operation above 2000 was fairly smooth. That makes me wonder about yours vibrating more above 2000. Almost sounds like something out of balance or not firing equally or something? Oh, are you propped for 3000 rpm at full bore operation? That is important to not lug the engine and it keeps things a little smoother. Other than that, unless you have a broken or bad motor mount I don't think the fancy mounts I installed are the answer to your particular problem. They would help of course. Will be interesting to hear what your "guru" finds.
Motor Mounts in M25
I have a 1985 32' with the M25. Two years ago I put on a 3 blade sailor for our travels around SF Bay and the coast. I was very pleased with the vibration reduction and after resetting the tach, pleased with RPMs. I do feel a fair amount of vibration at certain rpms. I was thinking about the 21 year old motor mounts, knowing that if they supported a chevy 350 I would replace them. I am planning a haul out in April and was wondering "how would one go about replacing them?" Can they be replaced one at a time if care is used? Do you have to lift the motor and do them all at once? What about possibly damaging the cutlas bearing?
I tend to learn by doing and have rebuilt most of the boat. At my vantage point the motor mounts shouldn't be that "big a deal" but since I believe in NOT solving problems that don't exist, I need some guidence.
Best to all
I have a 1985 32' with the M25. Two years ago I put on a 3 blade sailor for our travels around SF Bay and the coast. I was very pleased with the vibration reduction and after resetting the tach, pleased with RPMs. I do feel a fair amount of vibration at certain rpms. I was thinking about the 21 year old motor mounts, knowing that if they supported a chevy 350 I would replace them. I am planning a haul out in April and was wondering "how would one go about replacing them?" Can they be replaced one at a time if care is used? Do you have to lift the motor and do them all at once? What about possibly damaging the cutlas bearing?
I tend to learn by doing and have rebuilt most of the boat. At my vantage point the motor mounts shouldn't be that "big a deal" but since I believe in NOT solving problems that don't exist, I need some guidence.
Best to all
David,
First off swapping out motor mounts IS kind of a big deal. I had to to raise the engine up about 3 inches all around to get my tranny and bell housing off. There was considerable cutting of wire ties, disconnect some hoses and cables etc. to ensure I did no harm. I did not consider changing one mount at a time but it might be possible. As far as the cutlass bearing that should not be a concern since you have to disconnest the prop shaft at the transmission before lifting anything. And a carefull prop shaft realignment will be required before firing up again. I don't think there is any way to R&R mounts and not have to realign the shaft.
As far as 21 year old mounts - mine were the same age. Two of the 3 still appeared to be in good shape. The starboard rear mount was oil soaked and detioriating from years of the crankcase venting on it (that has now been redesigned by me). Now these new mounts I installed did solve the same "vibration at certain rpms" in mine that you are experiencing in yours. It might be worthwhile to do the swap. It was for me. The new Mounts are mostly "plastic" and the bushings are a softer plastic/rubber material. I do notice that the engine moves more "in the mount" at some rpms if I feel by hand while I am down by the running engine. I guess that means they are working huh.
You don't have to haul the boat to swap mounts. I built a motor lifting jig and did the tranny job and mounts while in my marina slip. I think that was easier than climbing a ladder in a boat yard. Personal choice. If you do this be prepared for the lag screws attaching the Mounts to be stripped or also, have been replaced by bolts and nuts. I found this which added to the job time. Cheers
First off swapping out motor mounts IS kind of a big deal. I had to to raise the engine up about 3 inches all around to get my tranny and bell housing off. There was considerable cutting of wire ties, disconnect some hoses and cables etc. to ensure I did no harm. I did not consider changing one mount at a time but it might be possible. As far as the cutlass bearing that should not be a concern since you have to disconnest the prop shaft at the transmission before lifting anything. And a carefull prop shaft realignment will be required before firing up again. I don't think there is any way to R&R mounts and not have to realign the shaft.
As far as 21 year old mounts - mine were the same age. Two of the 3 still appeared to be in good shape. The starboard rear mount was oil soaked and detioriating from years of the crankcase venting on it (that has now been redesigned by me). Now these new mounts I installed did solve the same "vibration at certain rpms" in mine that you are experiencing in yours. It might be worthwhile to do the swap. It was for me. The new Mounts are mostly "plastic" and the bushings are a softer plastic/rubber material. I do notice that the engine moves more "in the mount" at some rpms if I feel by hand while I am down by the running engine. I guess that means they are working huh.
You don't have to haul the boat to swap mounts. I built a motor lifting jig and did the tranny job and mounts while in my marina slip. I think that was easier than climbing a ladder in a boat yard. Personal choice. If you do this be prepared for the lag screws attaching the Mounts to be stripped or also, have been replaced by bolts and nuts. I found this which added to the job time. Cheers
Kim Schoedel
Member III
Jerry,
I have a Max Prop 2 blade. Have found that the gain in speed from 2000 rpm to 2500 produces little gain in hull speed. Assuming calm water and wind we get 6.3 kts at 2000 rpms and just gain .3 to .5 kts at 2500 rpm. I would like to know that I can run at the higher rpms if need be but that darn vibration over 2000 bugs me. Yes, it will be interesting what the guru finds.
I have a Max Prop 2 blade. Have found that the gain in speed from 2000 rpm to 2500 produces little gain in hull speed. Assuming calm water and wind we get 6.3 kts at 2000 rpms and just gain .3 to .5 kts at 2500 rpm. I would like to know that I can run at the higher rpms if need be but that darn vibration over 2000 bugs me. Yes, it will be interesting what the guru finds.
Kim,
Of course that folding Max-Prop is the cats meow for sailing. I guess what I would want to know is what is making the vibration at over 2000 rpm. I used a vibration meter called a "Sirometer" (vibrating wire kind of gadget) to confirm that my 2 blade prop was a thumping fool. Some math to predict the piston firing rate, engine rpm rate, prop shaft rate and blade rate past the strut then measuring the actual frequency does help tons in figuring these things out. If it is your prop then at best maybe it is out of balance, or bent or ?? and can be repaired. At worst you will have to live with it. For me, I like to sail, but end up motoring and swapping to a oh so smooth 3 blade sailor prop was a no brainer.
As far as engine rpms, If 2500 is your full power max and getting 6.7 to 6.8 knots, then for a M25 it is too low. As I recall (book on boat right now) Universal recommends the full power rpm to be 3000. If that is the case then you probably need less pitch in your prop (and maybe a smaller prop diameter to maintain proper hull to prop tip clearance (~15% of diameter )). I think your Max-Prop has a pitch adjustment. How nice. You may be able to tweak the pitch and dial in the full power 3000 rpm a lot easier than most us with fixed pitch props. Also with an E35 your hull speed may be higher than 6.8. Pitching for 3000 rpm max gets you a little more HP so you just might gain a little full power speed. Get your diving gear out?
Of course that folding Max-Prop is the cats meow for sailing. I guess what I would want to know is what is making the vibration at over 2000 rpm. I used a vibration meter called a "Sirometer" (vibrating wire kind of gadget) to confirm that my 2 blade prop was a thumping fool. Some math to predict the piston firing rate, engine rpm rate, prop shaft rate and blade rate past the strut then measuring the actual frequency does help tons in figuring these things out. If it is your prop then at best maybe it is out of balance, or bent or ?? and can be repaired. At worst you will have to live with it. For me, I like to sail, but end up motoring and swapping to a oh so smooth 3 blade sailor prop was a no brainer.
As far as engine rpms, If 2500 is your full power max and getting 6.7 to 6.8 knots, then for a M25 it is too low. As I recall (book on boat right now) Universal recommends the full power rpm to be 3000. If that is the case then you probably need less pitch in your prop (and maybe a smaller prop diameter to maintain proper hull to prop tip clearance (~15% of diameter )). I think your Max-Prop has a pitch adjustment. How nice. You may be able to tweak the pitch and dial in the full power 3000 rpm a lot easier than most us with fixed pitch props. Also with an E35 your hull speed may be higher than 6.8. Pitching for 3000 rpm max gets you a little more HP so you just might gain a little full power speed. Get your diving gear out?
Kim Schoedel
Member III
Thanks for the input Jerry. I am not sure what the hull speed should be on ours. Somewhere, I am sure on this site is the formula. I will do a search to see what I come up with.