Spitting Hunter

[R.Herman]

Simon, thanks for that bit of information. When I was inside the timing chest, if I recall correctly the cam looked to have very little "ramping" at the extremes. Kind of like a pair of fins.
When I first started trying to sort out the blowback issue I increased tappet clearance on the inlet valve to make sure it wasn't opening prematurely.

Good call on the brake actuating lever. That's one of the things I have not looked at since getting the bike. I'll check it out.

[paul.jameson]

Given that you have a single lobe cam, let us just eliminate one possibility for causing blowback. Your cam should NOT look like the one in the photo below. Specifically, it should not have the hollow main shaft or the drilling in the shaft opposite the lobe. If your cam has a solid main shaft and there is no drilling opposite the lobe, then, subject to Simon's comments, it should work satisfactorily, subject to whatever alterations are needed for your altitude.

[R.Herman]

Paul, my cam does not look like this one. I recall thinking that it had a pretty steep ramp profile.

Today's update: I put a couple miles on it today. On cold start it did not smoke from the exhaust but after it warmed up it smoked badly. And the scavenger pump was providing a steady stream of returning oil even after running for five or ten minutes. My understanding is that after initially clearing the sump there should only be bubbles returning.

[Simon.Gardiner]

...My understanding is that after initially clearing the sump there should only be bubbles returning.

Correct - another puzzle!

SG

[david.anderson]

As mentioned there are 2 versions of the VH single lobe cam, each requiring different tappet clearances. The first of the single lobe VH cams was the 1951 version which is a cast steel cam. The casting evidence is generally visible on the outside face of the cam as those that I have seen have not been machined there. This cam should be set with minimal tappet clearances, ie 0 - .002” at tdc.
The next single lobe VH cam is the 1954 version which is a forged cam that incorporates quietening ramps. Machining marks are always visible on the outside face of this cam. This cam has .006” and .008 tappet clearances however the instructions are “Rotate the engine forward in the driving direction until the exhaust valve just commences to lift and then adjust the inlet tappet to .006in clearance” then “Rotate the engine forward in the driving direction until the inlet valve just closes and adjust the exhaust tappet to .008in clearance”. IE the tappet clearances are not set at tdc.
Generally, the 51 cam when it commences to open does so fairly quickly. The 54 ramp cam has very looooong ramps with a very slow opening over about 40 degrees of engine rotation until the initial tappet clearance is taken up and then the opening rate becomes the same as the 51 version. You will not see any visible difference in the profile.
The checking clearances for valve timing are not the same as the running clearances. The checking clearance is .010” for the 51 cam and .023in and .025ex for the 54 cam.
You mention that you believe that the valve timing may be out. I do have a mk3 cam in which the timing mark or cam keyway is out by one tooth. So it is possible but likely, although who knows what may have been altered over the years. I have also seen a camwheel that had a timing dot on either side instead of just one side. Clearly someone had turned the wheel around and provided a new timing dot (correctly). 1 tooth on the camwheel gives 14.4 degrees of alteration.
However, I am a little confused. On page 1 of this thread you state “All I know is that when I checked, the timing marks on the cam and crank line up, and the cam has two lobes opposite each other. Don't know about the diameter of the base circle.” And yet later on page 5 of this thread you state “I read that for 1951 Ariel changed the cam and followers to a system with one-piece cam and a forked exhaust follower/lever with the inlet valve follower fitted inside the fork. My bike is titled as a 1948 model and the chassis number agrees with that, but my engine has the above-mentioned cam and followers.” So initially you are stating it is a twin lobe cam but later you are stating it is a single lobe cam.
For me if your bike is spitting back through the carb it can be a badly worn throttle slide or an incorrect valve timing. However any hot cam that has a lot of overlap will spit back fuel through an open bell mouth when blipped from low revs. A reground hot cam is always possible.
On page 1 you state “It only runs with the richest of the three main jets I have for it, and it wants the 106 needle jet and protests when I try to use a 105. This results in a black, sooty spark plug. But any attempt to lean the mixture results in hard or impossible starting and a refusal to run off idle. With the overly rich jetting it starts first kick (I have an electronic ignition fitted).” If the bike is difficult to start it should have very little to do with the needle jet. The idle circuit is separate to the rest of the carb although effects do flow through. Have you removed the jet block and cleaned all passages in it as well as the carb. Blocked idle circuit passages make for difficult starting. The over rich plug that you mention indicates that the needle jet size is wrong (for normal road speeds). What is the cut away on the slide. It should be 3 (3/16”)
However you have oil coming back out. For oil to be coming out the carb it can only be from the combustion chamber or from the inlet port. If you have an oversize oil pump there is a lot more oil going through the engine. You state that you have a constant flow back to the oil tank at idle and it does not settle to just bubbles. That sounds like a very oversize oil pump. With 3 compression rings and more oil flung at the underside of the piston that could be a problem. Ariel added an oil scraper in late 49 when they fitted a larger delivery side on the plunger pump. (those pumps are stamped 49A) and all later year models had a larger delivery pump. But if your oil pump is aftermarket with an even larger oil capacity still, unbedded rings and excess blow by then the symptoms you describe are possible. You could have the piston machined to fit the oil scraper that you have. That means not only increasing the ring width but also the oil drain holes for the ring groove. Or you could fit an original oil pump. It would be interesting to know the diameter of the delivery and return plungers in the pump. The other possibility, if you have tight valve guide clearance is a cracked head emanating from the valve guide hole, not likely but possible.
It also sounds strange to me that you can achieve suitable tappet clearances with pushrods being ¼” different in length. The tappets would have to be at opposite extremities.
Finally on page 3 you state “Tony: slippery oil = Castrol Classic GTX 20/50. Lots of zinc.” Ariel specify 40 or 50 monograde oil not a multi grade. 20w-50 is not as heavy as a 40 monograde oil and is not suited for use with a roller bearing bigend due to the loads imposed by the rollers.
David

[R.Herman]

David, thank you for your thoughtful and very detailed reply. I will try to respond to the various issues you raise.
For the record, my Red Hunter is an NH (350) not a VH.
I said I have a "double lobe" cam. That was based on my admittedly faulty memory. I THINK I recall seeing two opposing lobes when I was inside there a year ago. But I may be remembering incorrectly. I AM sure that the valve followers are of the forked variation.
Watching the steady stream of oil returning to the tank after running for a while did make me wonder of my Hawker pump is supplying more oil to the bottom end than is optimal. And I do have the original stock pump in my spares. I will check the dimensions of the bores of the two pumps. I believe my Clymer manual has specs on the stock part.
Living in the boondocks as I do, I cannot run out and buy monograde oil - nearest source is probably 150 miles from here. But I can buy some online.
Having my piston modified to fit an oil scraper ring would be worthwhile, but again, that's not a simple process from here. And other people with the 3-compression ring setup say it works fine for them, so I think I need to continue to look for the root cause of my problem.
As we all know, any motorcycle that has been through a number of owners over 70+ years can have no end of hidden modifications, and it's entirely possible that the timing marks on my gears are not correct. And the valve train may have been changed. My engine has the earlier 3-compression ring piston but the cam and followers that apparently were adopted for 1951, re: my manual.
And I don't know why there are two different length pushrods, but I am able to set clearances to nil and 0.002".
I will have to fit a degree wheel and thoroughly check and record opening and closing of each valve.

I did remove and clean out the jet block and ensured that all passages are clear. And as mentioned earlier in this thread, I tried swapping out to an Asian carb with no change in symptoms.
I believe I misspoke - It is only with the 107 needle jet that the engine will start easily (first kick) and take throttle. It will start with a leaner needle jet in place but will not accept throttle. I will have to check the number on the slide.
Thanks again. I really appreciate the knowledge here and very much appreciate your willingness to help me with this.

[nevhunter]

I've had nothing but WOE from oversized pumps and everyone I know has had the same problems when it was tried. A 350 is fine with the Pump fitted Prior to. 49. The Ariel's scavenge set up was never altered from the first fitting of it. It's far from optimum.. Nev

[R.Herman]

Nev, have you experienced the same kind of issues I have from oversized pumps? If that's my main problem it's an easy fix.

[R.Herman]

Today's update: I pulled the Hawker oil pump. Supply side plunger measures 0.325" diameter. I installed my used stock pump. Supply side plunger is 0.195" diameter.
Still spits back through the carb but exhaust smoke is reduced considerably.

[nevhunter]

You could have been getting oil in parts of the Carburetter that will affect the idle mixture. Remove the idle mixture screw and blow the passages out with clean compressed air. Nev