Mk3 Timing cover to Oil Pump Shimming

Hi all, I have read on many posts that sometimes there's the need to shim the oil pump seal out against the timing cover... With regard to the later Mk 3 timing cover is this process still required??
Now if shimming on the seal to cover is required and as this process is basically a "blind fit" .... how do you
1. Confirm what shim thickness is required
2. How to you know if too much shimming is installed or indeed more is required
3. Had a brief look through the manual and couldn't see any reference to this?

Thanks

Good questions, olympus, and not limited to the Mk3.
I have the AMR mod on my Atlas, and have Pondered questions 1 and 2.
I have used modeling clay to estimate the thickness of seal required, unsuccessfully.

I suppose the definitive test would be to measure cold oil pressure. If you can get 60 psi, it would indicate adequate sealing. If not, a shim would be required.

What if too much shim? ....... I dunno what downside and how you tell.

Slick

olympus said:

Now if shimming on the seal to cover is required and as this process is basically a "blind fit" .... how do you
1. Confirm what shim thickness is required
2. How to you know if too much shimming is installed or indeed more is required
3. Had a brief look through the manual and couldn't see any reference to this?

Click to expand...

0.010" of seal compression according to Service Release N.20 for the earlier seal. I'd guess the same for the Mk3 seal and cover.

The trick is to compress the seal but not so much that is splits. This is done with test fitting, buy a couple of seals and place the seal on the pump and put the timing cover gasket in place. Place on the timing cover and hold it firmly by pressing on the centre of the timing cover against the gasket and you should just be able to feel the gasket move laterally with your finger nail in the area of the oil pump, the front edge there should no movement. You can screw the cover into place, check it is fully sealed to the crankcase then remove it and check the compression on the seal. If you can see a compression mark around the seal and not too deep then that is ideal. Now replace the seal and refit the cover. In future you know that what you have works and as such you don't need to repeat it unless you change the oil pump or timing cover.
A good tip is always to replace the seal when you remove the timing cover, the reason is two fold, one it is good practice not to use a compressed seal, the other is that if it falls off with the oil into catch container when removing the timing you always ensure that a new seal is in place prior to fitting the timing cover.

L.A.B. said:

0.010" of seal compression according to Service Release N.20 for the earlier seal. I'd guess the same for the Mk3 seal and cover.

Click to expand...

Thanks Les, i take it the service bulletin fails to advise how you actually check this 0.010" compression.... if it was clearance that needed checking plastic gauge or alike could be used

Madnorton said:

The trick is to compress the seal but not so much that is splits. This is done with test fitting, buy a couple of seals and place the seal on the pump and put the timing cover gasket in place. Place on the timing cover and hold it firmly by pressing on the centre of the timing cover against the gasket and you should just be able to feel the gasket move laterally with your finger nail in the area of the oil pump, the front edge there should no movement. You can screw the cover into place, check it is fully sealed to the crankcase then remove it and check the compression on the seal. If you can see a compression mark around the seal and not too deep then that is ideal. Now replace the seal and refit the cover. In future you know that what you have works and as such you don't need to repeat it unless you change the oil pump or timing cover.
A good tip is always to replace the seal when you remove the timing cover, the reason is two fold, one it is good practice not to use a compressed seal, the other is that if it falls off with the oil into catch container when removing the timing you always ensure that a new seal is in place prior to fitting the timing cover.

Click to expand...

As a matter or engineering correctness i would always use a new seal,
I will attempt your advised on checking for the gasket movement between crankcase and timing cover
Thank you

olympus said:

i take it the service bulletin fails to advise how you actually check this 0.010" compression.... if it was clearance that needed checking plastic gauge or alike could be used

Click to expand...

What I suggest you do is fit the seal and the cover gasket then hold the cover in position and see which size of feeler gauge (if any) fits between the cover and the gasket near the pump.

L.A.B. said:

What I suggest you do is fit the seal and the cover gasket then hold the cover in position and see which size of feeler gauge (if any) fits between the cover and the gasket near the pump.

Click to expand...

I have always found this technique to be very subjective. I am hoping to find a more rigorous way.

Slick

You can't be more rigorous on such a large cover, its a case of pushing on the cover and by feel gauging if the seal is proving some resistance to the final locating of the cover onto the gasket. Push the cover on at an angle and you will struggle to feel the resistance, so I put 3 cover screws in and turn them all in the same number of turns so the cover goes on evenly, check the gap is even all around and 2 to 3mm before then pushing the cover on. If you then remove the pressure from the cover it should back out a small amount showing the seal in being compressed.

Its harder to describe than to do.

I have an old Mk 1 cover that i modified to become an idler support carrier..... i will look to modify this cover further so i can actually see the physical clearance between seal and timing cover ......but this may be in vain as the dimension of the oil pipe casting on the Mk 3 cover may differ

If using the same cover, just look at the old seal. If a new or otherwise different cover and you want to be anal-retentive, no seal, clay, cover on with gasket and tightened down. Remove, measure, and measure new seal.

I was told by AMR that there were changes to the covers over the years (pre-MK3) that can require shims. Also, if I remember right, there originally was no oil pump gasket so the engine/cover combination may add or remove the need for a shim.

I had one where I noticed no resistance when I put the cover on, so I fully tightened it and then removed it. It had almost no mark. So, I added one shim and tried again - it had the mark I expected. When I started the bike I what 60 psi.

On the other hand, I often flatten the cover on a surface plate and I've never seen a need for a shim after doing that.

A new gasket will compress upto 7-8% so those who want to use a feeler gauge feel free, if you get 0.006 - 0.007'' in then that will give around 0.010'' compression on the seal. As above, the gold plated check is to remove the cover, check the seal for even compression mark and replace it.
Always good practice to replace the seal, but you would be surprised how many don't for what is a low cost option. I believe one member here replaced a timing cover and had noticed the seal fall away into the catch container, the result was was expensive failure. That is why I suggest that every time the timing cover is removed then fit a new seal.

Madnorton said:

I believe one member here replaced a timing cover and had noticed the seal fall away into the catch container, the result was was expensive failure.

Click to expand...

But that was the result of someone placing a standard washer behind the seal, instead of a shim.

I recently bought a new seal and found it to be the wrong size. It had to be strongly stretched to open its hole to put it in place.
I felt that this could lead to it splitting later with loss of oil pressure. The Supplier replaced it for me

DennisMo said:

I recently bought a new seal and found it to be the wrong size. It had to be strongly stretched to open its hole to put it in place.
I felt that this could lead to it splitting later with loss of oil pressure. The Supplier replaced it for me

Click to expand...

For reference, who was the supplier... was this a genuine part??

I bought it in Canada and there was nothing on the plastic bag other than a felt pen part number.

Madnorton said:

The trick is to compress the seal but not so much that is splits.

Click to expand...

I've never heard of a new rubber gasket splitting due to being compressed. Have you witnessed that?
I would have thought that heat and age are the main factors causing a rubber gasket such as this one to split ....
Considering the heat the gasket is subjected to (110 degrees C has been mentioned), rapid decay is to be expected, if a low grade material is used.

O-rings are made of soft rubber and need to be compressed about 30% to form a seal. The present oil pump rubber gasket is made of harder rubber, and I'd expect a compression of about 15% to form a seal. If 7-8% is the final prescribed compression, that's a rather low value. Unless there are sharp edges causing marks, a compression of up to 15% should not cause lasting deformations on a new gasket IMO - provided the rubber quality has been carefully chosen.

Quote:
Compression set testing measures the ability of rubber to return to its original thickness after prolonged compressive stresses at a given temperature and deflection. As a rubber material is compressed over time, it loses its ability to return to its original thickness. This loss of resiliency (memory) may reduce the capability of an elastomeric gasket, seal or cushioning pad to perform over a long period of time. The resulting permanent set that a gasket may take over time may cause a leak. ... Compression set results for a material are expressed as a percentage. The lower the percentage, the better the material resists permanent deformation under a given deflection and temperature range. Compression set results can be confusing in that they are calculated different ways under different methods of testing.
(Ref. Stockwell Elastomers)

Preferred gasket materials for this application are HNBR and Viton. Both are oil resistant. The former endures service temperatures up to 150 deg. C, while the latter may endure temperatures well above 200 'C.

- Knut

mdt-son said:

Quote:
Compression set testing measures the ability of rubber to return to its original thickness after prolonged compressive stresses at a given temperature and deflection. As a rubber material is compressed over time, it loses its ability to return to its original thickness. This loss of resiliency (memory) may reduce the capability of an elastomeric gasket, seal or cushioning pad to perform over a long period of time. The resulting permanent set that a gasket may take over time may cause a leak. ... Compression set results for a material are expressed as a percentage. The lower the percentage, the better the material resists permanent deformation under a given deflection and temperature range. Compression set results can be confusing in that they are calculated different ways under different methods of testing.
(Ref. Stockwell Elastomers)

Click to expand...

Day one, Physics 101 the professor asked: "Which is more elastic, rubber or steel?" Assuming a trick question I was proud to the only one of about 30 that got it right. Of course, I had no idea why I was right! (Hint: Steel)

This is all about what is used to make the seal. For instance, Viton comes in many types and as far as I can tell, has no natural rubber. Also, Nitrile contains no natural rubber and there are at least five types of Nitrile.

I have no clue what the AN oil pump output seals are made from but I'm guessing one of the forms of Viton due to the required temperature, hardness, and elasticity.

Greg, I doubt Viton was ever considered by NV due to cost and general acceptance back then. Invented in the late 50's and gaining popularity in the 90s, it's more likely NV kept what Norton chose in the 50's, and I guess it's NBR. Same story as with valve stem seals, probably.

- Knut

Temperature ratings:

Material.............................Deg.F........................................Deg. C

Viton ................................. 450 ......................................... 232

Neoprene ...................... 225 .......................................... 107

Nitrile (gen. purpose) 250 ............................................ 121

From this data, general purpose nitrile or neoprene is barely within expected operating temperature. Viton is the safer choice, but as Knut has stated above, NV likely used the materials generally in use at the time. These worked adequately well then, and would likely be adequate now.

Slick