Shock absorber knocking

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Gui.dorey
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Re: Shock absorber knocking

Postby Gui.dorey » Wed May 29, 2019 5:52 am

Bob.Murphy wrote:Changing to Mk II guides might be an answer (if they fit - I didn't do this and don't know the respective dimensions). Alternatively, getting new guides turned-up with a top that allows the rubber 'valve guide seals' that one gets in car engines to be fitted would be a better option.


MKII guides don't fit! I installed new guides on mine but Drags sent me the wrong ones for the MkII by mistake. I only noticed after having the engine assembled that something was wrong, as I couldn't turn the camshaft a full rotation. The valve collars were hitting the top of the guides, so the valves wouldn't open fully and blocking the movement of the rockers/pushrods. I had to disassemble the head and mill the top of the guides down to the MKI dimensions.... I have a thread on here with all my head scratching questions at the time.

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Re: Shock absorber knocking

Postby john.whiting » Wed May 29, 2019 6:40 am

GD,that is called fitting.....you dont just throw a british bike together and expect it to be right straight off.......you carefully check fits and clearances ,and free rotation.......but on a completely different subject.......I would not bother fitting exhaust stem seals to a cast iron 4,I did that and the seals disintegrated from the heat,and were useless.......intake seals were OK .But that is what I call hot running.maybe its just the climate here...........I was offered my old 4 back,but at 3 times what I sold it for.....said "no thanks....a single will do me".

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Re: Shock absorber knocking

Postby camstevens » Wed May 29, 2019 9:57 am

Thanks, this is really helpfull....I'm going to try a couple more tests this weekend: oil pressure regulator (currently not relieving) timing, fuel + take timing/inspection cover off and check plain mains. If this doesn't resolve the issue or reveal any root cause, I'm afraid this new engine I've put my heart, soul, blood, sweat and now tears into us going get carefully disassembled again.

Looking at Nev and Roland's comments above, there was no significant wear in the stems.....it's not that. I won't be able to check spring clearances, etc again until it's apart, but I wonder if a stem shroud could be achieved through brazing a sleeve to the base of the spring retainer plate? Assuming there is space for this, it would only work if the majority of oil isn't running straight down the stem from the top of the retainer plate.

Just a thought

Cam

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Re: Shock absorber knocking

Postby Gui.dorey » Wed May 29, 2019 10:28 am

Hi Cam,

you could always try this - again from the Sq 4 Workshop manual. No idea if works.

However, I still find it hard to believe that so much oil is flowing down the stems on a newly rebuilt engine. On mine, which was just rebuilt as well, and using a Morgo pump, I just had some leakage at the rocker covers. There was absolutely no sign of oil getting into the combustion or the spark plugs oiling up - and I ran it several times for up to 10-15min on the stand in my garage.
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Bob.Murphy
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Re: Shock absorber knocking

Postby Bob.Murphy » Wed May 29, 2019 10:46 am

Interesting :!:

So the sliding sleeve is replaced with a fixed tube, the valve collar then just fits into the top without touching it (no over-revving allowed here ;) ).

My question is - Oil WILL get into the tube, but how does it get out without providing a permanent head of oil around the valve stem which is the exact opposite of what one wants :?: .

Or am I missing the point somewhere :? .

Bob.
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Re: Shock absorber knocking

Postby camstevens » Wed May 29, 2019 11:01 am

Yes Bob
I think we're both missing a trick here :). You could also fit a Viton o-ring on the stem directly below the spring retainer.....

I go back to my previous.....is the oiling primarily caused by pooling or running down the stem?. The modifications above suggests the former....but.....

Cam

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Re: Shock absorber knocking

Postby Knud.Degnbol » Wed May 29, 2019 11:51 am

Or am I missing the point somewhere :? .

Yes, I think so. The tube is a tool to mount the valve guide.

I have tried oil retainers once on my cast iron square. After few kms I looked after them. The had totally disintegrated due to heat. Luckily I could pick all of them up before they disappeared into the innards of the engine.

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Re: Shock absorber knocking

Postby john.whiting » Wed May 29, 2019 12:34 pm

A modern stem seal is designed to spread a thin but even film of oil on the stem..........some here may remember the old hard rubber "umbrella" type seals in cars of the 60s and 70s.......in my Falcon,they caused galling and scoring of the exhaust stems,but removing them caused much smoke from starting,and especially if caught in thick traffic,when every acceleration caused a puff of smoke.

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Bob.Murphy
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Re: Shock absorber knocking

Postby Bob.Murphy » Wed May 29, 2019 4:49 pm

Knud.Degnbol wrote:Or am I missing the point somewhere :? .
Yes, I think so. The tube is a tool to mount the valve guide.


I thought that might be the case - but the title is "Modification to MkII valve guide" - and the rest looked standard to me.

So just what is the modification :?: :? .

More confused than ever now :D .

Bob.
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Re: Shock absorber knocking

Postby paul.jameson » Wed May 29, 2019 8:06 pm

I am fairly sure that the over-oiling problem will be found to be due to the very high oil pressure. The rockers and shafts will be partly worn so the high oil pressure will send a large amount of oil into the rocker boxes and thence down the valve guides.

As a first step, I would get a new pressure relief valve spring from Drags or Bruce Longman and fit that. I have a rough and ready test rig for these valves consisting of a length of brass rod which the pressure relief valve screws into one end. At the other end I have soldered in an old tyre valve stem. This allows me to test the pressure relief valve using the tyre inflator on my compressor. There is obviously some difference in performance between air and oil but you get a good enough idea of when the spring is somewhere near correct.

The only other contributory factors I can think of are blocked oilways in the tappet guides or a blocked oilway leading from the outside of the front crank plain bearing down into the sump. I would have assumed though, that these oilways would have been cleaned out when the engine was rebuilt.

Presumably, you have a decent oil return to the tank so that the sump is not filling up with oil?
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