Author Topic: GB is not OK!  (Read 5423 times)

Offline RogerSB

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Re: GB is not OK!
« Reply #60 on: 26.05. 2018 11:23 »
Good news and no doubt a relief for GB that there is consensus that he can safely use his later camshaft and with some benefit *smile*.

Just as a matter of interest . . . and before things move on can anybody briefly say what the difference is between the earlier and later camshafts (apart from the pt no), i.e. completely different shape to profiles or just higher peaks to the lobes, etc?

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Online tlmark

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Re: GB is not OK!
« Reply #61 on: 26.05. 2018 11:29 »
Wow GB you ripped into sorting this well done

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Re: GB is not OK!
« Reply #62 on: 26.05. 2018 11:56 »
G'day Roger
Inlet opens before tdc closes after bdc. Exhaust opens before bdc closes after tdc.
334 inlet has 280 degrees duration, exhaust 270 degrees, 55 degrees overlap (both valves open)
356   "      "  284       "           "            "       284     "        79     "           "
357   "      "  299       "           "            "       295     "        88     "           "
358 I don't have figures and I don't have lift figures at hand. I think Rocket Racer may have that info.
Cheers
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Offline RogerSB

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Re: GB is not OK!
« Reply #63 on: 26.05. 2018 12:52 »
Thanks for that Musky  *respect*, I was just curious what the difference was. So to my un-technical details understanding - the valves are open to both inlet and exhaust for slightly longer?

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Re: GB is not OK!
« Reply #64 on: 26.05. 2018 12:57 »
So, better breathing then?

Online RichardL

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Re: GB is not OK!
« Reply #65 on: 26.05. 2018 15:42 »
Take a look here for the various cam profiles versus valve opening:

http://atlanticgreen.com/bsamain.htm
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Online morris

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Re: GB is not OK!
« Reply #66 on: 26.05. 2018 16:14 »
So, better breathing then?
I always understood that the speed of the burnt gases leaving the cylinder helps sucking in the fresh mixture, hence the overlap. This would mean though that the overall fuel consumption will rise if there’s more overlap.
I also wonder if the carb would need to be jetted differently?
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Re: GB is not OK!
« Reply #67 on: 26.05. 2018 16:23 »
I don't know if I should create a fresh thread, but. I'm cleaning bits-n-bobs. I've removed the spring loaded check valve in the timing side case. I missed that when I restored the engine six years ago. The bits all looked good but I'm going to order a new ball and spring. I understand that I should lightly tap the ball into its seat to make sure the seal is as good as possible.

I was wondering if I should pull the oil suction pipe out to clean the galleries more thoroughly. Is the top end locked into the case with a glue?

Offline RogerSB

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Re: GB is not OK!
« Reply #68 on: 26.05. 2018 16:39 »
I also wonder if the carb would need to be jetted differently?

I must admit that did cross my mind also, Monobloc 276 vs 389 *dunno*.

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Re: GB is not OK!
« Reply #69 on: 26.05. 2018 16:40 »
Sludge! I'm not sure how many miles I've done * in the last six years since I cleaned the sludge trap but this is what came out today. Probably not a problem but it goes to show that even with an external filter and monograde oil the sludge trap is still doing a good job.

* An indication of my mileage is given by how long you expect Avon SM and Speedmaster tyres to last because they are getting a bit low on tread!

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Re: GB is not OK!
« Reply #70 on: 26.05. 2018 16:45 »
Quote from: Morris
I always understood that the speed of the burnt gases leaving the cylinder helps sucking in the fresh mixture, hence the overlap. This would mean though that the overall fuel consumption will rise if there’s more overlap.
I also wonder if the carb would need to be jetted differently?

There’s more to long duration cams than the overlap (period when both valves are open, although yes, the inertia of the departing exhaust charge reduces pressure in the combustion chamber and starts to draw the fresh charge in. Overlap also allows some of the more complicated sonic effects of a tuned exhaust.

Early opening of the inlet valve before TDC means it’s already open by a useful amount when the piston starts to descend.  Late closing of the inlet valve after BDC allows the inertia of the incoming charge to cause cylinder filling to continue after the compression stroke has started.  This effect needs a few 1000s of rpm to work: at idle and low rpm, late closing of the inlet has the ill-effect of allowing mixture to be pushed back out through the inlet ports and carburettor. Mixture being blown out through the carb and then sucked back in causes richness that fouls plugs in traffic jams.

Early opening of the exhaust valve before BDC on the power stroke lets the gases start to be expelled by their own expansion pressure, at a time when they won’t do much more useful work pushing the piston down.

Are we back where we started?

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Re: GB is not OK!
« Reply #71 on: 26.05. 2018 16:53 »
There’s more to long duration cams than the overlap (period when both valves are open, although yes, the inertia of the departing exhaust charge reduces pressure in the combustion chamber and starts to draw the fresh charge in. Overlap also allows some of the more complicated sonic effects of a tuned exhaust.

Early opening of the inlet valve before TDC means it’s already open by a useful amount when the piston starts to descend.  Late closing of the inlet valve after BDC allows the inertia of the incoming charge to cause cylinder filling to continue after the compression stroke has started.  This effect needs a few 1000s of rpm to work: at idle and low rpm, late closing of the inlet has the ill-effect of allowing mixture to be pushed back out through the inlet ports and carburettor. Mixture being blown out through the carb and then sucked back in causes richness that fouls plugs in traffic jams.

Early opening of the exhaust valve before BDC on the power stroke lets the gases start to be expelled by their own expansion pressure, at a time when they won’t do much more useful work pushing the piston down.

Are we back where we started?

Are you talking about more extreme cams than my 67-356?

Offline RogerSB

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Re: GB is not OK!
« Reply #72 on: 26.05. 2018 17:09 »
I was wondering if I should pull the oil suction pipe out to clean the galleries more thoroughly. Is the top end locked into the case with a glue?

When I bought SRMs magnetic sump filter the instructions said put a ring spanner over the scavenge pipe to move it forwards or backwards to align it with the hole in the filter. Mine moved easily and was obviously swivelling, so I would assume it's a press fit. The instructions to move it left or right was to tap it with a hammer.  I'm not sure if that bent the pipe sideways to align it or moved it in and out of the hole. All I can say is that it was easy and worked fine. Others may be able to give you more precise explanation.

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Re: GB is not OK!
« Reply #73 on: 26.05. 2018 19:50 »
I've been online and ordered piston rings, big end shells, cam followers, gaskets and seals.

I still need sludge trap plugs and oil check valve spring and ball and clutch centre tab washer.

Today, after emptying and filling the dishwasher and reassembling brother-in-laws mower motor I have been mostly scraping old gasket off and decoking the combustion chambers. I will strip, decoke and regrind the valves when I get my new spring compressor. When I have all the new parts I will be carefully washing parts in something suitable, blow drying and wrapping in plastic bags ready for a surgically clean rebuild.

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Re: GB is not OK!
« Reply #74 on: 26.05. 2018 20:06 »
Jeez GB, they say that women are good in multitasking but you are the living proof of the contrary...  ;) *smile*
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