Author Topic: Tappets playing maracas?  (Read 1822 times)

Offline roadrocket

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Tappets playing maracas?
« on: 23.06. 2015 20:07 »
Hello

I know alloy heads are more noisy than iron. My tappets primarily emits a sound like water boiling or a constant zizzle. But sometimes another noise kicks in, like Mick Jagger playing maracas while under the influence. It lasts for 3-30 seconds, then dies down and leaves the scene for the background zizzle. Why is that? Head is renovated in my time of ownership, and deemed fine by a specialist last year.

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Online RichardL

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Re: Tappets playing maracas?
« Reply #1 on: 24.06. 2015 00:40 »
This will be a guess that needs backup to be taken seriously, but perhaps it is a case of barrels and head heating faster than the pushrods and, therefore, getting taller faster. Additionally, the coefficient of expansion for the alloy head is much greater than the iron barrels or steel pushrods, adding to the getting-taller-faster equation.

It would be fun to be right, but looking forward to being corrected, if it must be.

Richard L.
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Offline East_Coast_BSA

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Re: Tappets playing maracas?
« Reply #2 on: 24.06. 2015 02:21 »
I think that changes in lash due to thermal expansion would last longer than 30 seconds and would only happen once.  I drain my sump if the bike sits more than a few days.  It's noisy when it starts and for the first 15-20 seconds or so, then I get return oil in the tank and there is pressure to the rocker arms.  Once everything is heat-soaked, you shouldn't hear any difference.  I set my lash at .008" intake and exhaust.  I checked it once hot and it was ~.012".  I attributed that increase to the aluminum head (coefficient of expansion, aluminum vs. steel).  Interesting variable to throw into the mix.
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Offline Rocket Racer

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Re: Tappets playing maracas?
« Reply #3 on: 24.06. 2015 04:00 »
Hello

I know alloy heads are more noisy than iron. My tappets primarily emits a sound like water boiling or a constant zizzle. But sometimes another noise kicks in, like Mick Jagger playing maracas while under the influence. It lasts for 3-30 seconds, then dies down and leaves the scene for the background zizzle. Why is that? Head is renovated in my time of ownership, and deemed fine by a specialist last year.

Just a possibility but bent pushrods could cause intermittent noise if they were rotating/clashing. And if a new noise could have resulted from last reassembly...
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Offline duTch

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Re: Tappets playing maracas?
« Reply #4 on: 24.06. 2015 08:48 »

 I think I know the sound and randomness that you mean; dunno if it's from (1)mine now and I've gotten used to it, or (2) on previous incarnation, or (3) on my original Rocket.. , but if option (2) as opposed to option (1), I did change my pushrods when I rebuilt due to a slightly bent one....*dunno*, but I'll keep a fine tuned ear next lap, and hope Mick leaves the maracas at home *smile*

 Easty_C;
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I drain my sump if the bike sits more than a few days.
  How much do you drain out...? I measured mine after a run before I changed the oil last time, and got 150ml/~5 oz's...if you don't get significantly more than that, I'd suggest you may be doing a disservice, as the way I see it, a bit in the sump would have the benefit of allowing some to fling around and make a mess and lube the insides on startup...or am I playing with the wrong fiddlesticks...??
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Offline The Artful Bodger

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Re: Tappets playing maracas?
« Reply #5 on: 24.06. 2015 09:44 »
I can't help with your rhythmic tappets I'm afraid but....  Certainly not a good idea to drain the sump oil unless it wet sumps enough to blow out of the breather! The noisy 15-20 seconds is your engine wearing itself out, the greatest wear on an engine is when first stated due to the lack of oil.
   With oil in the sump, from the first turn of the crankshaft most of the engine is getting some lubrication from splash (remember some basic lawnmower engines only have splash lubrication) straight away. Drain the oil and it's grinding away totally dry until the pump has built up some pressure, then the oil's got to find its way to the bores, small ends etc. through big end leak and splash.
  Fortunately my Ariel doesn't wet sump, although I ride it several times a week all year round. However if it did I would put a container under the bike to catch any oil which would be blow out and feel good that the engine was nice and oily when it started up.
Colin
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Online Butch (cb)

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Re: Tappets playing maracas?
« Reply #6 on: 24.06. 2015 10:51 »
I got a bit confused myself with all of this. I’d presumed that the clearances were there, and set cold, such that at a normal operating temperature they were pretty much running at nil. On my Nimbus the exhaust side are set at a whopping 28 thou. Being exposed rocker gear (but OHC) they are easily checked when hot – and I find they are still highly rattily. So presumably they are set up like this for the cam ramps design. But why?
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Offline duTch

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Re: Tappets playing maracas?
« Reply #7 on: 24.06. 2015 11:54 »
  Col, we're on the same page, but what I had thought to say is that (I think) some later makes of bike have small rubber bits between the fins, and even cast-in bits of ally and I believe that's to dampen the rattle  some... *????*

 Won't fix any problems, but might make it quieter
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Started building in about 1977/8 a on average '52 A10 -built from bits 'n pieces never resto intended -maybe 'personalised'
Have a '74 850T Moto Guzzi since '92-best thing I ever bought doesn't need a kickstart 'cos it bump starts sooooooooo(mostly) easy
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Offline a101960

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Re: Tappets playing maracas?
« Reply #8 on: 24.06. 2015 12:33 »
Quote
Certainly not a good idea to drain the sump oil unless it wet sumps enough to blow out of the breather!
Maybe, but unless you check how much oil is actually in the sump how are you going to know if there is enough oil in there to get blown out of the breather? I have seen this happen and it makes a hell of a mess. The other little problem that arises is that there is potential to pressurise the crank case and maybe blow an oil seal. We all of course have our preferences and prejudices. I run my bike on Silkolene 20/50 fully synthetic oil http://www.opieoils.co.uk/p-1123-silkolene-comp-4-20w-50-xp-synthetic-ester-based-4-stroke-engine-oil-for-high-performance-motorcycles.aspx which is formulated specifically for old engines. It ain't cheap, but I balance that against the cost of an engine rebuild. One of the characteristics of fully synthetic oil is that it clings to the surfaces and eliminates the lack of lubrication on start up.
John
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Online RichardL

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Re: Tappets playing maracas?
« Reply #9 on: 24.06. 2015 13:59 »
The noisy 15-20 seconds is your engine wearing itself out, the greatest wear on an engine is when first stated due to the lack of oil.

Agreed, regarding the period just after startup being when there is greatest potential for wear, but have some doubts about that being the cause of the noise in question. Were that the case, Roadrocket would have said the noise happens right at startup then goes away. Leaving relative pushrod/head growth out of this, I believe that the amount of clatter coming from pushrod/rocker-cup contact is about the same for a given clearance regardless of how wet the cup is. I doubt that the amount of oil there would be enough to damp the sound from the rod tapping the cup and then radiating from both the rod and the entire length of the rocker arm. However, the gap between them will make a big difference. I think if you take a ball-peen hammer and hit a steel plate with ball end, the radiated sound would show little difference whether the plate was dry or oiled. I'm going to try it later just to be sure I haven't slipped a cog.

Richard L.
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Offline bikerbob

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Re: Tappets playing maracas?
« Reply #10 on: 24.06. 2015 17:41 »
 If you drain the sump of all oil and then start the bike, then for a few seconds there will not be a return of oil and seeing as the rockers are fed by the return feed then they could be starved of oil until it gets up there so you could have noisy tappets for a few seconds. I was told a number of years ago that the oil pressure to the rockers is only about 5lbs because it is on the return feed and when you rebuild an engine on first start up you should hold your finger over return hole in the oil tank for a few seconds to force oil up that small pipe to the rockers and clear out all the air. I have always followed that advice.
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Offline East_Coast_BSA

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Re: Tappets playing maracas?
« Reply #11 on: 24.06. 2015 17:55 »
 Oil has Five distinct jobs.  It Lubricates, Cleans, Cools, Seals and Deadens Noise.  Basic lawnmower engines have "Dipper Rods", they literally scoop the oil and force it into the bearings.  They don't have oil pumps.  Having oil sloshing around the crankcase of a conventional engine doesn't lubricate anything.  It's actually detrimental to the performance of the engine.  The film of oil between the bearings and the journals provide the lubrication that's required.  Any oil splashing around the outside of the crank/rods doesn't "find" it's way into crank journals.  It's physically impossible for any oil to creep into a gap that's oil a few thousandths wide, especially while it's spinning.  As soon as the engine starts, there is oil pressure that's forcing oil through all the passages.  In a wet sump application, whatever oil is in the sump doesn't provide anything except a source of oil.  You don't want oil slopping around the crank while it's running, that's why performance engines have Windage Trays.  It keeps the oil from the sump from splashing on the crankshaft.  The dry sump system is a better design because it keeps the crankshaft from running in oil, which is the entire purpose.  The return oil being the source of lubrication for the rocker shafts is minimal.  It's not subject to direct oil pressure, but return oil pressure which takes longer to generate.  This is not a real issue because the design does work.  They may not have oil pressure immediately after start up, but a 10 or 15 second delay is not a problem.  At idle the rocker shafts don't see a tremendous load and they do have an existing oil film.  Add to that they have a very limited range of motion.  They aren't spinning around like a crank or connecting rod.  The oil has a tendency to stay put.  As long as there is a healthy film of oil on the bearing surface, there is no problem.  The rest of the overhead could run almost dry.  I'm sure you've seen the pictures of the antique engines that run without valve covers and have an exposed overhead.  BSA engines were designed to run with enough oil in the sump to supply the return pump and distribute some oil to the rockers.  Theoretically as soon as the run-off oil hits the bottom of the sump. it's gone.  I used to see 6-8 ounces of oil in the sump after a few days.  Over time, it has gotten better and sometimes it may only be four ounces.  I may be able to wait longer before draining the sump, but it's just a habit.  I remember when I was young, my father would let the bike sit and he'd put a baking pan under the motor.  When the engine started, there was oil everywhere.  At least I can prevent that now. 
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Offline duTch

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Re: Tappets playing maracas?
« Reply #12 on: 24.06. 2015 18:46 »

 
Quote
  Having oil sloshing around the crankcase of a conventional engine doesn't lubricate anything.......  Any oil splashing around the outside of the crank/rods doesn't "find" it's way into crank journals. ...

 Fairly obvious, but I was thinking of the bores and rings and stuff- but this is a intermittent noise story, let's not get sidetracked... Otto when does this noise happen; at any particular stage of running...?
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Started building in about 1977/8 a on average '52 A10 -built from bits 'n pieces never resto intended -maybe 'personalised'
Have a '74 850T Moto Guzzi since '92-best thing I ever bought doesn't need a kickstart 'cos it bump starts sooooooooo(mostly) easy
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Online Greybeard

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Re: Tappets playing maracas?
« Reply #13 on: 24.06. 2015 19:04 »
Re    East_Coast_BSA last post: If you have a look on YouTube there are many videos of idiots >:D running engines without oil and at full rev's until they go kaput. It really is quite amazing how long an engine will run without oil. Well not really without oil, there obviously must be enough oil film to keep them going for a while.   *work*
Examples:
https://youtu.be/3WLOccckJ5o
https://youtu.be/snrrdIL3DdI
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Offline roadrocket

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Re: Tappets playing maracas?
« Reply #14 on: 24.06. 2015 19:15 »
Hello all

Thanks for all the input, great with such interest! The noise happens at all stages during a run - though I have only done trips of less than one hour, but that should see the engine hot anyway. I am fairly sure the push rods are fine, as the engine was rebuilt not long ago. The rods are SRM. The bike gets used often enough, and I don't drain the sump. I think the sound only occurs at speeds up to 70 mph - from there I tend to have my attention elsewhere. The oil pump was checked in very fancy test rig our BSAOC chairman invented, and has passed the test. I need to do a long trip and take better note of whether the "maracas" incidents gets less frequent as the engine heats up. The bores and pistons are the same as before the rebuild, the bottom end was the trouble here, so a hone and new rings was the only work done to the cylinders. So the consensus is on the noise stemming from piston slap? This should not happen if everything was OK and the engine warm I guess?

Otto in DK
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Otto in Denmark