Mk3 Timing cover on a Mk2 engine, anything to pay attention to?

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Jagbruno

Jagbruno

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Hello all,

The engine on my road/racer is a 850 Mk2 that has been upgraded in period, crankshaft professionally lightened and balanced for my slimline frame, rockers lightened, head flowed, polished conrods, it had a Dunstall PD04 camshaft when I bought the bike, since replaced by a PW3. It is a fast bike, gps-clocked at 130Mph/-213km/h on the Dijon circuit a couple of years ago.
It is by far the best motorcycle I have ever riden, giving me constant exhilaration.

The engine has a recurring drawback, it wet-sumps very quickly, about 600ml overnight, the oil pump has been rebuilt several times, but it is simply wornout at this stage.

So I bought a brand new one from Andover and Yves (of Big Spender 920cc fame) will install it for me next week.

As it says in the title, my engine is a '73ish MkII 850 but it has a MkIII timing cover.
Could this be in any way cause for concern or is there any potential snag that we need to specially pay attention to?

Thank you in advance!

Mk3 Timing cover on a Mk2 engine, anything to pay attention to?
 
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Jagbruno said:
Hello all,

The engine on my road/racer is a 850 Mk2 that has been upgraded in period, crankshaft professionally lightened and balanced for my slimline frame, rockers lightened, head flowed, polished conrods, it had a Dunstall PD04 camshaft when I bought the bike, since replaced by a PW3. It is a fast bike, gps-clocked at 130Mph/-213km/h on the Dijon circuit a couple of years ago.
It is by far the best motorcycle I have ever riden, giving me constant exhilaration.

The engine has a recurring drawback, it wet-sumps very quickly, about 600ml overnight, the oil pump has been rebuilt several times, but it is simply wornout at this stage.

So I bought a brand new one from Andover and Yves (of Big Spender 920cc fame) will install it for me next week.

As it says in the title, my engine is a '73ish MkII 850 but it has a MkIII timing cover.
Could this be in any way cause for concern or is there any potential snag that we need to specially pay attention to?

Thank you in advance!

Mk3 Timing cover on a Mk2 engine, anything to pay attention to?
Click to expand...

The MK3-850 dumps the excess oil from the oil pressure relief valve into the timing chest.
A 72-850 dumped the excess oil back into the inlet passage to the oil pump.
If you put a MK3 side case onto a 73 engine you must plug the port that feeds the oil back to the intake passage. This is done with a 1/4 inch socket head set screw. Otherwise the engine will wet sump as soon as it's shut off.
You also need the larger flange on the oil pump outlet to fit the MK3 type seal. Jim
 
comnoz said:
A 72-850 dumped the excess oil back into the inlet passage to the oil pump.
If you put a MK3 side case onto a 73 engine you must plug the port that feeds the oil back to the intake passage.This is done with a 1/4 inch socket head set screw. Otherwise the engine will wet sump as soon as it's shut off.
Click to expand...

It would 'wetsump' if the timing cover gasket in the area surrounding the oilway was damaged, same as a pre-Mk3 case/cover would.

It's a good idea to blank off the oil gallery when using a Mk3 timing cover but it isn't absolutely necessary to prevent wetsumping as the Mk3 T/S crankcases had the identical oilway drilling that pre-Mk3 T/S cases have.
The Mk3 timing covers aren't usually drilled to match (except for one or two odd Mk3 timing covers you appear to have as we've done this one before). :)

https://www.accessnorton.com/NortonCommando/zero-oil-pressure-to-head.15817/#post-228545
 
L.A.B. said:
It would 'wetsump' if the timing cover gasket in the area surrounding the oilway was damaged, same as a pre-Mk3 case/cover would.

It's a good idea to blank off the oil gallery when using a Mk3 timing cover but it isn't absolutely necessary to prevent wetsumping as the Mk3 T/S crankcases had the identical oilway drilling that pre-Mk3 T/S cases have.
The Mk3 timing covers aren't usually drilled to match (except for one or two odd Mk3 timing covers you appear to have as we've done this one before). :)

https://www.accessnorton.com/NortonCommando/zero-oil-pressure-to-head.15817/#post-228545
Click to expand...

From what I was told after the first go around, it seems some of the new MK3 replacement covers were drilled in both places and required the setscrew to plug one hole or the other. I don't know if there are any more of that cover around now.
The cover that came on my MK3 was drilled both places. The person I got the bike from said it was that way when he bought the bike new.
 
Thank you very much Jim and L.A.B. Yes, I have the proper larger MkIII seal, not sure what you mean by larger flange.
Yves and I will have a close look at the situation when we'll open the timing cover next week. I hope we will be able to locate the passage Jim describes and that plugging it won't lead to a problem, as I have no way to tell if the timing cover and engine are otherwise stock.
I didn't have the time to read the other thread yet, but when I'm done, if still confused, I might ask you for a drawing showing exactly which oil way to plug and what 'hole' to look for to be absolutely sure we don't goof up.
Thank you again, and Jim, Yves and I sincerely hope that your health problems are behind you!
 
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Jagbruno said:
Yves and I will have a close look at the situation when we'll open the timing cover next week. I hope we will be able to locate the passage Jim describes and that plugging it won't lead to a problem, as I have no way to tell if the timing cover and engine are otherwise stock.
Click to expand...

This.
Mk3 Timing cover on a Mk2 engine, anything to pay attention to?

It should be threaded. If the Mk3 timing cover is the usual type (not Jim's :)) then there should be no corresponding oilway in the cover so the case gallery is effectively blanked off when the cover is in place as long as the gasket surrounding it isn't damaged.
However the fact that it drains 600ml/cc overnight with a Mk3 cover even with a worn pump suggests something isn't right.
 
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Thank you for the drawing, L.A.B.!
So to make sure I understood correctly, that hole is the one we should plug?
(Not that I am stupid, but when it come to oil circulation I would rather appear stupid in front of the (Norton) world rather than take the slightest risk for my beloved engine!)
:eek:
 
Jagbruno said:
So to make sure I understood correctly, that hole is the one we should plug?
Click to expand...

Yes, when a normal Mk3 timing cover is fitted (no oilway drilling) the crankcase oilway drilling in the diagram can safely be blanked off as the blow-off from the OPRV goes into the timing chest instead of being returned to the inlet side of the feed pump.
 
Ok, thank you very much. Assuming it exist, wouldn't it be safer to plug the hole in the cover rather than in the crankcase?
Anyway, we most probably won't open the timing cover until next week, but when we do I'll post pictures and comments!

In the meantime, bright sunshine and big blue sky over Brussels, so I might take the old girl for a spin this afternoon!!
 
Jagbruno said:
Assuming it exist, wouldn't it be safer to plug the hole in the cover rather than in the crankcase?
Click to expand...

There shouldn't be any hole in the normal Mk3 cover (look at gtiller's RH picture).
 
Jagbruno,
You asked about the flange on the oil pump. I justed wanted to bump that question so you get a response.
I’m not 100% sure on this but I think the spigot coming from the pump that the seal rests on is larger on the MKIII. I’m sure someone will know for sure and get back to you.
Pete
 
The older one measures 1/2 inch in diameter whereas the MK3 one is just under 3/4 inch

It is the same diameter as the new larger but flatter seal and without it, the seal would not push flat against the timing cover.

Mk3 Timing cover on a Mk2 engine, anything to pay attention to? Mk3 Timing cover on a Mk2 engine, anything to pay attention to?
 
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Deets55 said:
You asked about the flange on the oil pump. I justed wanted to bump that question so you get a response.
I’m not 100% sure on this but I think the spigot coming from the pump that the seal rests on is larger on the MKIII.
Click to expand...

Yes, it is. The 066193 850 Mk3 pump is the only one AN sell (when in stock) even for Dominator and Atlas so it must be suitable for all big twins. The wider spigot flange is unlikely to cause a problem when used with the earlier cover/seal but the spigot can be changed if necessary.

https://andover-norton.co.uk/en/shop-drawing/452/dommi-engine-500-600cc#
(Pump Item 98)
 
We still haven't open the timing cover, next week probably, but I found this picture from a few years ago when we rebuilt the engine, definitely showing that there is no plug in 'the hole'. Obviously, the crucial point is to have a look at the timing cover!

Mk3 Timing cover on a Mk2 engine, anything to pay attention to?


However, there is one less hole on my case compared to gtiller's image, left from the oil pump there is only one hole, the bottom one is 'missing'.
Crankcases number is 304xxx.
 
Jagbruno said:
We still haven't open the timing cover, next week probably, but I found this picture from a few years ago when we rebuilt the engine, definitely showing that there is no plug in 'the hole'. Obviously, the crucial point is to have a look at the timing cover!

Mk3 Timing cover on a Mk2 engine, anything to pay attention to?


However, there is one less hole on my case compared to gtiller's image, left from the oil pump there is only one hole, the bottom one is 'missing'.
Crankcases number is 304xxx.
Click to expand...

Is that the correct mk111 oil pump to timing cover seal? It looks like a pre mk111 one to me...
 
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