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ENGINE MOUNT VIBRATION POSITION

henriquerv9

henriquerv9

Active Member
HI ALL,

I AM GOING TO INSTALL THE ENGINE ON THE MOUNT TODAY. I HAVE A DOUBT. WICH SIDE OF THE VIBRATION MOUNT GOES TO THE ENGINE SIDE AND WICH SIDE GOES TO FIREWALL SIDE? I DIDNT FOUND IT ON FIREWALL FOWARD MANUAL. THERE'S A SOFT AND HARD. THE HARD ONE IS THA THE ONE WITH A STEP ON THE OUTSIDE D.


ANY HELP WITH ME APPRECIATE


HENRIQUE
 
Henrique,
The hard one goes behind the mount on top and on the forward side on the bottom. The easy way to remember is that with the engine sitting static, it pulls down on the top mount and compressed the bottom one.
 
So..........................................

As ours are in symmetrically - i.e. the soft side forward on the upper and lower mount, do we have a problem :(
 
If you have the soft ones between the engine and the mount on the bottom, they will tend to compress and you will get excess engine sag.
 
I believe one of the chapters in the back of the construction manual shows exactly how the mounts should be positioned. There is also a large area washer that has to be installed between the engine and each bottom lord mount.
 
I have an older RV6 Preview Plans Set with the following very useful SK-90A diagram on page 11-14. Couldn't find it any where else. Hope it helps.
Jim Sharkey
Last 10% RV6 Tip-up O360-A1A
sk90aig7.jpg
 
As the front and rear cushions appear to be of different thicknesses, I think we will leave as is because otherwise the baffles and cowl will not line up. I may get some aerobatic mounts which are of a harder nature and slip them into the bottom forward mounts if we have a sag problem.

We have built in a 3/8" sag allowance already so fingers crossed.

We screwed up but unscrewing it will cause more problems :eek:
 
mike newall said:
As the front and rear cushions appear to be of different thicknesses, I think we will leave as is because otherwise the baffles and cowl will not line up. I may get some aerobatic mounts which are of a harder nature and slip them into the bottom forward mounts if we have a sag problem.

We have built in a 3/8" sag allowance already so fingers crossed.

We screwed up but unscrewing it will cause more problems :eek:
Click to expand...

Maybe Not...

I have never seen an engine sag 3/8 ". It is usually more like 1/8", occassionally 3/16". (are their builders out there that are recommending that you compensate by 3/8"?

Swapping the parts around would reduce your compensation amount and get you closer to what the actual sag will eventually be.
 
Notice the washers!

As the front and rear cushions appear to be of different thicknesses, I think we will leave as is because otherwise the baffles and cowl will not line up.
Click to expand...
That's why the J221861 washers are in differernt positions top and bottom. As shown in diagram above, the washer goes between the engine and the inside hard cushion on the bottom, thus making up the thickness difference between the two cushions.
If you put the washers in the rear, top and bottom, in your installation, swapping them and installing as shown above should not change your engine position enough to amount to anything.
 
Last edited:
Not exactly...

rvpilot said:
That's why the J221861 washers are in differernt positions top and bottom. As shown in diagram above, the washer goes between the engine and the inside hard cushion on the bottom, thus making up the thickness difference between the two cushions.
If you put the washers in the rear, top and bottom, in your installation, swapping them and installing as shown above should not change your engine position enough to amount to anything.
Click to expand...

If there is no washer on the front at the bottom then there are other problems.
There is a step milled into the case where the bottom lord mounts attach. A washer must be used in this location to act as a spacer to account for the step. If this is not done, there will be a gap between the mount half and the engine case.
 
Thanks for correcting me!

Thanks Scott, didn't realize there was a step there. Always thought it was just to make up thickness difference. Know now!
If he's got both washers on the back, even more reason to fix the mistake!
 
Last edited:
No - the washers and bolt lengths are perfect - they are all detailed in the box that came with the mounts - we have just got the soft cushion in front of the mount on the lower mounting.

I will ask Lord at Sun n Fun next week but I am loath to change anything now as it will create lots more problems than it will solve. If it sags a bit, we will tackle that problem later by jacking up with washers below.

Can't imagine we are the first, or the last to do it.
 
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