ET: Engine (Twin) Leak down test

Bill Thomas

Well Known and Active Forum User
VOC Member
I went round Ron's house once, And he showed me start up, On a small BSA Two stroke,
With NO float, When I told Him some years later, I used them with NO float He told me off !.
Can't remember the float height He said they should have, I thought it was the middle of the hole ??.
Sounds like yours was lower ?.
I got on better with the early square body, But then I bought a pair of 30mm then 32mm, With the later body,
I sold a pair to Dave Jones, North London for his racing outfit, That went well !!.
 

greg brillus

Well Known and Active Forum User
VOC Member
Thanks for the info on the Gardner's.........well mine is a 40 mm type "C" like the one in Tim's pic above........I am using a Dellorto SS 1 type float bowl that flows over a liter of methanol in one Minuit the level is supposedly correct at about 6 mm above the jet at full throttle. Remembering that the slides pull from the top down........40 mm should be fine given my engine is a 665 cc 92 x 100 bore and stroke........Crank triggered Ignitech programmable ignition set up with twin coils firing twin plugs.........Getting back to the TP heads which is what i have on the racer.......the seals could have either come loose and not sealing and/or damaged.......They sit in a machined recess in the top of each guide and this area is well bellow the stock guides and will readily draw oil down them if there is a problem. They are a modified Harley seal that has had the lower section that presses over the guide in the Harley head cut off........this leaves a small button shaped seal.......even the seal part has to be cut down as it is designed for 0.312" valves not 0.372" as ours are....... I had to use a wad punch and sit the seal on a mandrel to locate it as best I could and then cut the hole in the seal larger. When you remove the valves from the head you need to place a slim fork shaped spanner like device that stops the stem collar from crushing this small seal that is easy to damage if you bang the valve out as per normal........ I asked Terry about these seals once and he was reluctant to give any info about it........So I looked into it myself to find out what it was........In my opinion it is less than ideal........ I will try to come up with something better when I get the chance.
 

davidd

Well Known and Active Forum User
VOC Member
David, as ever your insight is great. You make me wonder if the stem seals are letting oil in. I'll make a point of inspecting them when the valves are out.
Cheers Bill
Bill,

That is very kind of you, I do think that regardless of the leak down test that I would be unhappy with the oil that is finding its way into the combustion chamber. I think that the stem seals are one of those items worth checking. I have never used stem seals, but I don't seem to have the guide clearance that will let oil through.

I hope that you achieve the reliability that you are looking for from an Egli!

David
 

Cyborg

Well Known and Active Forum User
VOC Member
Have the numbers for the D Smith/J McDougall seals
Glen

Are these the type of seals you are referring too? On the end of the mandrel before it gets modified. If so, can you share the number? I filed it in a safe place.

Valve Guide retainer and stock seal.jpg
Seal mandrel.jpg
 

Monkeypants

Well Known and Active Forum User
Non-VOC Member
Yes, that's the seal, well proven on Vincents now.
SKF 3688.
I believe this was a another Dan Smith innovation, one that John McDougall made good use of.
Between the Dan and John rebuilds , these seals must have been tested for hundreds of thousands of miles in many Vincents.

 
Last edited:

Bill Cannon

Well Known and Active Forum User
VOC Member
Well, the plot thickens.
Had to go to work to get the valve spring compressor from my "metric" toolkit.
Now removed the valves and guess what? No stem seals at all and apparently no facility for fitting them (see photo). Does anyone know better?
Valve seats look OK the exhaust seat was a bit dark but appears flat and ground easily with a quick zip of fine paste.
Inlet seat is clean but a lot of carbon on the intake side of the valve head (see photo).
By feel, there's no detectable play in the guides.
I've only done the rear head at the moment, I'll strip the front this afternoon.
It seems I won't have much choice but to put it back together and see how we go.
Maybe I need to open an account with Honda for the combustion chamber cleaner!

Cheers Bill
 

Attachments

  • 003.JPG
    003.JPG
    246.7 KB · Views: 34
  • 004.JPG
    004.JPG
    246 KB · Views: 35

timetraveller

Well Known and Active Forum User
VOC Member
Bill, it might be the quality of the photograph but I cannot see either the two holes or two cut out to take a tightening tool for the upper part of the guide. If you have never seen the recess for a seal then it is a cut out below the lock ring, perhaps 2 to 3mm deep. All the lock rings I have seen designed to take a seal have the two circular holes for the tightening tool, rather than the milled slots.
 

roy the mechanic

Well Known and Active Forum User
VOC Member
Bill, it may be worth looking down the guide to see if there is an o ring in a groove trying to impersonate a seal. Several repro race motors have them. Roy.
 
Top