M25 motor mounts

Ekutney · February 08, 2016, 01:21:36 AM

I have read all the previous posts on changing from OEM stiff motor mounts to Ventus mounts, either the K75 or combination of K75 & K50. Most of those posts go back a couple of years, does anybody have an update how the mounts lasted & if there was any resolution to the engine shaking at idle?

Roland Gendreau · February 08, 2016, 07:48:42 AM

I replaced my mounts in 2012, so I have 3 seasons of running on them. They have held up just fine.
I never had a problem with the engine shaking at low RPM's and still do not.

Ekutney · February 08, 2016, 06:31:57 PM

Roland,

What mounts did you use?

Roland Gendreau · February 08, 2016, 08:15:06 PM

I installed the K75's. i installed them one at a time, and it did not require hoisting the engine or disconnecting the exhaust. Of course the shaft needed to be re-aligned afterwards.

Ekutney · February 09, 2016, 03:12:59 AM

How did you get the old mounts off without lifting the engine? I read a previous post that explained cutting the bolts on the old mounts then taking the new mounts apart.

http://c34.org/bbs/index.php/topic,7920.msg54936.html#msg54936

Is this the technique you used?

Roland Gendreau · February 09, 2016, 10:38:18 AM

Yes, that is the method I used. I put the new mounts in a vice and removed the threaded shafts. I used a sawzall (harbor freight) to cut the shafts of the old mounts to remove them. I did not need to use a hacksaw on any of them, but obviously you have to be careful the saw doesn't hit something inadvertantly. The shafts are pretty soft and cut easily. Once the base of a new mount is lagged down, just insert the new threaded shaft through the motor bracket, thread on a nut, put on some thread locking stuff on the end of the shaft and screw it into the mount. The threaded shaft can be tightened into the base with an allen key. I snugged the nuts a little more than hand tight , then went through the shaft alignment after all mounts were in place.

Ron Hill · February 09, 2016, 02:09:31 PM

Ed : The reciprocating saw method and taking the mounts apart works well. I've changed mounts both ways.

However, make sure that you sweep the area with a magnet to pick up all the iron saw filing. If you don't tiny rust spots will eventually appear!!

A thought

Ekutney · February 15, 2016, 05:59:43 AM

I had a diesel mechanic come by to look at the engine and give me an estimate for adjusting the valves. He made a suggestion I would like to share and get some feedback. He said the motor mounts were fine but they were walking because the lag bolts were not holding the mounts firm. I said I would either use longer bolt or drill and glass it over then drill. He said I should just use through bolts and explained one of the bolts on each side had already been done, showed me I could see this through the access holes at the rear of the stringers.

First two pictures show the motor mount with access to rear and the through bolt from under the stringer.

He then suggested I could drill two large holes in the front of the stringer to allow access to the front mounts, these are shown as the two large circles.

My question is has anyone ever heard of this or actually tried it? It sounds like a feasible idea but I have no idea how thick the front of the stringer is or how thick the top of it is. I can get a close guesstimate by comparing inside measurements to outside but I am not a contortionist and it is not easy working behind the engine.

Ekutney · February 15, 2016, 06:03:35 AM

Looks like I used the same pic twice on my original post.

I meant the last picture to be the following showing two black circles as potential locations to drill access holes.

Stu Jackson · February 15, 2016, 10:33:02 AM

Ed, I would be very hesitant to cut holes in the vertical face of the stringers. IMHO, those are the main supports for the front of the engine. OTOH, one could "argue" that the longer sides provide the support.

Here's what I've done: http://c34.org/bbs/index.php/topic,5538.msg34486.html#msg34486

The concept of even having a nut down below is brand new to me, and I'll have to go look soon at my port aft mount to see if that's the case. Since all discussions of this have always mentioned LAG BOLTS, having nuts down below seems counter-intuitive.

I've felt that as long as the silicone is keeping the lag bolts from loosening, it should suffice. The weight of the engine keeps them down and they are working more in shear to keep the engine in place fore & aft.

Ekutney · February 15, 2016, 11:48:22 AM

Stu,

I would agree but one of the current bolts on each of the rear mounts have already been changed to thru bolts. It would make sense to use a large fender type washer to spread the force and through bolt from the bottom up leaving a stud so that only a nut with a lock & flat washer has to be used. A circular hole should not weaken the structure which comes from the sides & corner. The picture of the back of the stringer looks to be a bit of a hack job and not very professional.

Ron Hill · February 15, 2016, 01:17:41 PM

Ed : It's hard to be that your 30 year old engine mounts are still at their prime!!

I do not exaggerate when I say that the new mounts I installed change the engine running so much-- I thought I was on a different boat!!

I'd change the mounts - my thought

Ekutney · February 15, 2016, 03:49:37 PM

Ron,

Am going through maintenance records and have a call into PO. The mounts have been replaced just not sure when. The issue is you can see the mounts have moved and the forward lag bolts do not tighten. What do you think of the idea of through bolts from the bottom using large fender washers or such for backing? Through bolts are in 1 of the 2 mounts for each of the aft mounts. It is not possible to get to them via the rear access, would need a child's arm to even get close.

Ron Hill · February 16, 2016, 02:43:25 PM

Ed : The first time I replaced my engine mounts here's how I did it. Maybe an Idea for you.

I disconnected the drive shaft and only lifted the front of the engine up high enough to remove the mounts and replace them. With the old mounts removed I "wiped" some epoxy on the walls of the lag-bolt holes and install new lag-bolts that were 1/2" longer to get a better "bite" into new wood. It worked just fine.

You might also try to figure out why the original lag-bolts are not holding - oil? fuel? prestone? leakage into the holes? - over tightening? - no lock washers ???

Again, I can't emphasize the difference between the new mounts and the old style mounts!! The new mounts absorbed the vibration rather than transmitting it all to the engine stringers and the hull!!

A few thoughts

Ekutney · February 16, 2016, 08:24:14 PM

ron,

You said:

"I disconnected the drive shaft and only lifted the front of the engine up high enough to remove the mounts and replace them."

Did you lift the rear of the engine to replace the rear mounts?

"With the old mounts removed I "wiped" some epoxy on the walls of the lag-bolt holes and install new lag-bolts."

Did you let the epoxy cure before you installed new longer lag bolts?

I take you comment that the new mounts made a HUGE difference. Did you replace al 4 old mounts with K75 mounts?