The BSA A7-A10 Forum

Technical => A7 & A10 Engine => Topic started by: roadrocket on 23.06. 2015 20:07

Title: Tappets playing maracas?
Post by: roadrocket 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.

Title: Re: Tappets playing maracas?
Post by: RichardL 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.
Title: Re: Tappets playing maracas?
Post by: East_Coast_BSA 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.
Title: Re: Tappets playing maracas?
Post by: Rocket Racer 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...
Title: Re: Tappets playing maracas?
Post by: duTch 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;
Quote
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...??
Title: Re: Tappets playing maracas?
Post by: The Artful Bodger 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
Title: Re: Tappets playing maracas?
Post by: Butch (cb) 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?
Title: Re: Tappets playing maracas?
Post by: duTch 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
Title: Re: Tappets playing maracas?
Post by: a101960 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
Title: Re: Tappets playing maracas?
Post by: RichardL 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.
Title: Re: Tappets playing maracas?
Post by: bikerbob 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.
Title: Re: Tappets playing maracas?
Post by: East_Coast_BSA 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. 
Title: Re: Tappets playing maracas?
Post by: duTch 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...?
Title: Re: Tappets playing maracas?
Post by: Greybeard 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
Title: Re: Tappets playing maracas?
Post by: roadrocket 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
Title: Re: Tappets playing maracas?
Post by: East_Coast_BSA on 24.06. 2015 20:24
At those speeds, how sure of you where the noise is originating from?  Do you think it's coming from the rocker box area or somewhere in the bottom end?  You also have to remember that all the drive gears are straight cut, not helical.  They are anything but quiet.  Maybe you're getting some "Backlash" in the gear train due to harmonics?  Is the noise consistent throughout the RPM range or is it louder at some points?  Accelerating, decelerating, steady state?  It's really a tough game when your engine isn't silent when it's running correct.  There always seems to be some noises going on.  Just makes things more difficult to find.
Title: Re: Tappets playing maracas?
Post by: RichardL on 24.06. 2015 20:42
Otto,

I don't recall piston slap coming into the conversation. During my last top-end work I ended up overhoning by at least two thou past book recommendations of "rebore cyclinders and replace pistons." I replaced the rings and all seems pretty good. No particular obvious slapping, so, if slap was the problem on your bike one might have to assume radical overhoning. Personally I don't think that's it. Right now, if it is actually a problem noise and not a usual noise, my bet is on rocker clearance adjustment being accidentally too big. In any case, at least that's easy to check.

Richard L.
Title: Re: Tappets playing maracas?
Post by: duTch on 24.06. 2015 22:25
 I don't recall piston slap mentioned either until now. ... But I just had a thought that I've had a noise the past few weeks that I've been attributing to primary chain, but my dynamo belt flogged itself last weekend..... So you have a belt or a chain...?
  Someone (jachenbach?), had that issue recently
Title: Re: Tappets playing maracas?
Post by: roadrocket on 25.06. 2015 08:40
I read some of the remarks on different expansion rates as a hint to piston slap, I was obviously wrong there. So much for the better. The noise mostly occurs at 40-50 mph, and I rarely go faster than 65, however, I did do a stint on the motorway, and didn't pay any attention to noises there. All went fine at 75-80. My dynamo drive is SRM belt. I will try to make a video to record noises. The one I am worried about should maybe be described as a bit like a cicada living somewhere near the right hand side top end.
Title: Re: Tappets playing maracas?
Post by: duTch on 25.06. 2015 08:43

 Chronic Tinnitus...?
Title: Re: Tappets playing maracas?
Post by: KiwiGF on 25.06. 2015 11:30
Long shot but could you have duff push rods? There were definitely some duff ally rods in the marketplace for quite a while which had an incorrect radius on the ends causing the rods to stick in the cups and rattle......
Title: Re: Tappets playing maracas?
Post by: roadrocket on 25.06. 2015 11:34
I'll check the tappet clearances again, and try to check the rods also.
Title: Re: Tappets playing maracas?
Post by: East_Coast_BSA on 25.06. 2015 12:10
The one I am worried about should maybe be described as a bit like a cicada living somewhere near the right hand side top end.

The cicada noise mine was making turned out to be a head gasket.
Title: Re: Tappets playing maracas?
Post by: Butch (cb) on 25.06. 2015 12:23
The one I am worried about should maybe be described as a bit like a cicada living somewhere near the right hand side top end.

The cicada noise mine was making turned out to be a head gasket.

Ah yes, I've had that on mine. Used to chirrup under load only. Initially only under heavy load but then became more prevalent as the gasket further deteriorated.
Title: Re: Tappets playing maracas?
Post by: a101960 on 25.06. 2015 13:16
Same here. No visible sign of anything wrong either. In my case the gasket had failed between the cylinders, and has been said, initially it started when the engine was under load. It then progressed to happening every time I opened the throttle especially on a gradient.
John
Title: Re: Tappets playing maracas?
Post by: RichardL on 25.06. 2015 13:34
So, compression test.
Title: Re: Tappets playing maracas?
Post by: roadrocket on 25.06. 2015 16:03
Head gasket! That sounds very plausible, thanks for that! Any point in trying to retorque the head?
Title: Re: Tappets playing maracas?
Post by: RichardL on 25.06. 2015 16:13
Compression test first, I believe. You wouldn't want to take off the rocker box just to tighten the head bolts only to discover that was not the cause.

Richard L.
Title: Re: Tappets playing maracas?
Post by: roadrocket on 27.06. 2015 13:23
OK, a compression test showed 150 psi in both cylinders. But that does not rule out a clattering head gasket I believe?
Title: Re: Tappets playing maracas?
Post by: RichardL on 27.06. 2015 14:45
Others may know better, but I think that pretty much rules out the head gasket.

Richard L.
Title: Re: Tappets playing maracas?
Post by: Triton Thrasher on 27.06. 2015 15:08
Others may know better, but I think that pretty much rules out the head gasket.

Richard L.


It does not rule out a blowing gasket.

Combustion pressure is much higher than compression pressure.

That's why the engine runs and powers a bike.
Title: Re: Tappets playing maracas?
Post by: Butch (cb) on 29.06. 2015 12:31
So that was a pointless test then?

If I was going to pull the rocker box to tighten the head bolts I'd pull the head for a look at this point anyway.
Title: Re: Tappets playing maracas?
Post by: RichardL on 29.06. 2015 13:26
Others may know better, but I think that pretty much rules out the head gasket.
Richard L.
It does not rule out a blowing gasket.
Combustion pressure is much higher than compression pressure.

TT,

Appreciate that excellent point, but trying to reckon the mechanism in a blowing head gasket that leads to intermittent  "maracas". On the other hand, pinging is something that occurs intermittently. I wonder if that's something to consider as the noise source?

Richard L.
Title: Re: Tappets playing maracas?
Post by: muskrat on 29.06. 2015 21:03
Good point Richard, it could/might be pinging (detonation). Otto, retard the ignition timing a few degrees or use a higher octane fuel (or a booster for your fuel).
Cheers
Title: Re: Tappets playing maracas?
Post by: roadrocket on 30.06. 2015 06:53
Yes, I know how pinging sounds in my MG, and I have had the problem on my B 40. If this is pinging however, it is a much metallic sound than the clicking sounds I have experienced before. I will try to adjust the cam ring, a pour some octane booster in.
Title: Re: Tappets playing maracas?
Post by: Joolstacho on 10.07. 2015 05:45
I once had a similar problem, which sounded a bit like excessive tappet clearances but different. I checked and re-checked them, I was running dural pushrods so at first I suspected something there, but in the end it turned out to be as follows. When I got the bike the camshaft (357) was worn, so I had a local cam-grinding company (Wades, Melbourne, remember them?) to regrind my camshaft, -they had a 357 grind pattern so all seemed ok. But what I hadn't realised was that, although they reground the cams correctly (I checked using a timing wheel), the grinding process had removed a touch too much height off the camshaft, resulting in the tappets not following the cam profiles at the lowest point of the cams, and the tappets were clattering against their 'stop' screws on the base circle positions. More to the point, I think I may also have had Wades regrind the tappets too (wish I could remember exactly what it was, sorry I can't be more precise, but I know it was one or both of these things).
All fixed when Bob Joyner sent me a shiny new 357 camshaft!
Title: Re: Tappets playing maracas?
Post by: bsa-bill on 10.07. 2015 08:23
Quote
If this is pinging however, it is a much metallic sound

Pinging in my experience on my RGF (alloy head) was a very metallic sound, I'd go as far to say that it's a sound that you would not associate with combustion,

Title: Re: Tappets playing maracas?
Post by: duTch on 10.07. 2015 09:27

 That's good point JoolsT, and something that was discussed a couple of years (or so) ago- I can't remember if I addressed it on my rebuild or not, but always in the back of my mind

 Can you do me a favour and edit/modify this..?...sound like you 'wrecked it'.. *conf* makes me think of any Wreckless Eric song
Quote
.......excessive tappet clearances but different. I checked and recked them,.....
Title: Re: Tappets playing maracas?
Post by: Joolstacho on 10.07. 2015 09:53
Har, har Dutch, you are so right and I am suitably admonished!!! Spelling fixed. Sorry. (Though I might have 'recked' a few things in my time this wasn't meant to be one of them).

(The funny thing is I used to work as an Art Director in ad agencies, and used to have a whale of a time going 'round looking over copywriter's shoulders correcting their crap spelling.
Point is that I was a supposedly an illiterate arty bastard, and they were supposed to be the literate good spellers! They actually knew sweet F.A. about the Queen's English!

I was in a major national retail store yesterday, and was amazed to see a large row of very expensive lit signs displaying some tosser's confusion with the plural and the apostrophe.
How do these people get away with it? It's gone all the way from basic design through artwork to lightbox backlit signage without anyone picking it up.

Don't get me started!!!!
Title: Re: Tappets playing maracas?
Post by: muskrat on 10.07. 2015 10:02
Any more than 60 thou off the cam base circle or followers (or both combined) will give you that Jools.
An old fella once described pinging as sounding like a stick being rattled around in a jam tin. Not far off.
Cheers
Title: Re: Tappets playing maracas?
Post by: RichardL on 10.07. 2015 19:06
B,b,but, the overzealous cam grinding would not seem to explain intermittent maracas (or, are they really castanets and Roadrocket's bike is haunted by Flamenco poltergeists?)

Richard L.
Title: Re: Tappets playing maracas?
Post by: muskrat on 10.07. 2015 21:26
The intermittent bit sugests pinging. Under load up a hill or acceleration.
Cheers