Yanmar 2GM20 - Centre of Gravity

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SteveIOW

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Am about to renew the engine mounts (not Yanmar mounts) on my 2GM20 that I originally installed 21 years ago. I know the engine + gearbox dry weight is 106 kg but what I would like to know is where the Longitudinal Centre of Gravity (LCG) is situated. Can't find this specified in any of the documentation I hold on the engine. Once the engine is removed from its existing mounts and in the cabin I could support it at its tipping/balance point and obtain LCG position but I would rather know the position and obtain the mounts before starting the job. Am not looking for help in selecting the mounts. Just want to know where the LCG is. Does anyone out there know please.
 
SteveIOW said:
Am about to renew the engine mounts (not Yanmar mounts) on my 2GM20 that I originally installed 21 years ago. I know the engine + gearbox dry weight is 106 kg but what I would like to know is where the Longitudinal Centre of Gravity (LCG) is situated. Can't find this specified in any of the documentation I hold on the engine. Once the engine is removed from its existing mounts and in the cabin I could support it at its tipping/balance point and obtain LCG position but I would rather know the position and obtain the mounts before starting the job. Am not looking for help in selecting the mounts. Just want to know where the LCG is. Does anyone out there know please.
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Can't you just jack up the rear change 2 then jack up the front and change those 2?
 
I don't think that's the point. The stiffness of the front and rear mounts is different to allow for its being heavier one end than the other.

Of course, you could loosen the existing mounts and weigh each end of the engine separately.

Rob.
 
Yes Rob, your second sentence is the point I'm getting at. The 2GM20 Manual states that the Yanmar mounts (I don't have room to fit these) have an identification number 100 on the forward mounts an 75 on the aft mounts. From the position of the engine feet I can well believe that there is more load on the forward mounts than the aft mounts but would like to know if the weight distribution is 55:45, 60:40, 70:30 etc. Am still hopeful of someone knowing the position of the Longitudinal Centre of Gravity but the meanings of 100 and 75 on the Yanmar mounts would be better than nothing.

Steve
 
That info would certainly have been available to Nav Archs and builders. Have you asked Yanmar? If you can find the % split for a similar engine I think that you could assume that it's close enough as long as you haven't got seven alternators and four fire pumps! There isn't much special about a diesel engine, but do bear in mind that the mount positions will have an effect.
 
Steve
I suspect we have been conversing on another forum.
The c.o.g is stated in the repair manual and you may be able to find a copy via google
I can tell you that on a 2YM15 with conventional gear it is 166mm horizontally from the a/v mount centreline (air filter end) and 93mm above the crankshaft centreline .
On an 2YM15 with SD20 gear it is 237 mm horizontally from the a/v mount centreline (air filter end) and 25mm above the crankshaft centreline
Hope this helps
Martin
(P.M. me with your mobile if you want a chat)
 
CoG is a problem, I had a 4 cyl ford with heavy flywheel and PRM box, the CoG was at the rear engine feet, so it just gyrated about that point. The solution would have been to put the engine on a raft with feet well behind the GBox.
 
SteveIOW said:
Yes Rob, your second sentence is the point I'm getting at. The 2GM20 Manual states that the Yanmar mounts (I don't have room to fit these) have an identification number 100 on the forward mounts an 75 on the aft mounts. From the position of the engine feet I can well believe that there is more load on the forward mounts than the aft mounts but would like to know if the weight distribution is 55:45, 60:40, 70:30 etc. Am still hopeful of someone knowing the position of the Longitudinal Centre of Gravity but the meanings of 100 and 75 on the Yanmar mounts would be better than nothing.

Steve
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Do you really need to know the Longitudinal Centre of Gravity (LCG) just to replace the feet? I know both Yanmar mounts are different hardness rubbers but when I replaced my 2GM20 engine mounts I contacted R&D Marine who supply flexible couplings and engine mounts with regards to my replacements and the chap advised replacing my existing feet with R&D Super mounts. He said that they had had really good results from them over the years, and at less than a 1/4 of the price of Yanmar feet I thought I would try them. Having had them now for 4 years they are as good now as first installed, but you do need a packer underneath them to make them the same height as Yanmar ones. They also cut down the amount of vibration at low revs, and I have found them an excellent replacement.
The feet go in the same mounting holes on the engine as the Yanmar ones but just a little higher - so why do you need to know the balance point?

The chap to speak to is Roger Firth, very helpful chap

Photos available of the install if any help.

Philip
 
Had a quick flick through the workshop manual and can't find anything about the subject there. I still think the only way to determine the COG is to hoist each end with a spring balance.

Rob.
 
rob2 said:
Had a quick flick through the workshop manual and can't find anything about the subject there. I still think the only way to determine the COG is to hoist each end with a spring balance.

Rob.
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Have a careful look at the general arrangement drawing in the front of the manual - it (COG) should be shown as a small circle divided into 4 quarters with each quarter alternating black and white - at least it is on mine
 
When my old Bukh was replaced with a Yanmar 3GM30 I encountered a lot of new vibration, probably due to the big change in engine mounting stiffness. It was originally set up with different rubber hardness front and rear but in an effort to overcome the vibration the softer ones were replaced with harder, making all four the same. It made little difference to the vibration and the mountings have remained that way ever since.
 
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