High Cylinder Head Compression

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rog60
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Sun Jul 19, 2009 9:39 pm

Divided into three questions really:-

1.Can a high cylinder head compression ratio cause pre-detonation? ( I think the answer to that is yes!!).

2. Is there an 'idiot's' guide to calculate the compression ratio?

3. How do you reduce/compensate for high compression if there is no cylinder head gasket?

Anyone?
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rog60
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Sun Jul 19, 2009 10:31 pm

Thanks, better find the caclculator :D.
Would using a higher octane fuel/octane booster help to compensate for pre-detonation?
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Knowledge
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Sun Jul 19, 2009 11:31 pm

Yes.

Retarding the ignition also helps, as does taking steps to avoid fuel starvation (high flow fule tap, adequate float valve size etc).
Martin

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rog60
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Mon Jul 20, 2009 12:22 am

Thanks guys. That'll keep me occupied for a while. :D :D :D :D
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tony
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Mon Jul 20, 2009 3:09 am

remember to add squish gap volume.
on larger bore motors this can add up to a lot.
best way is to fill motor with oil from a burette when at tdc for un corrected to bottom of sparkplug hole.(as long as the plug dont protrude miles into the head that is-which is bad o course)
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rog60
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Mon Jul 20, 2009 10:40 pm

Cheers guys.
O.K.
I still have an annoying metallic tinkling/rattling sound from my Casa 210 kit so I dismantled the top end. The piston crown and cylinder head have oily, part congealed med brown deposits on them, the piston is a firm, not tight fit to the bore. Piston rings are within tolerances. The piston moves up and down the barrel very smoothly with no marks on the bore or piston and the gudgeon pin is a firm push fit through the piston bosses and small end bearing. There is plenty of oil in the bore and coating the piston. There is no pitting or any other marks on the smooth surface of the piston crown or cylinder head. The spark plug is very dark brown and slightly oily at the edges.
I have carefully altered the ignition (currently set at 19DBTDC) downwards to 16DBTDC in 1 degree increments) with no alteration to the sounds I am hearing but the engine not eager to run evenly below 17DBTDC.

Am I being paranoid or after 30 odd years of dealing with Lambrettas really hearing the engine 'pink' ? The above sound only occurs on acceleration to about mid RPM range and some times on just open throttle settings.

In conclusion, there is no visible mechanical sign of 'pinking' so am I just hearing different engine noises with an Aluminium barrel. My mates who do know a liitle about the engines think so. But if they are wrong and I am right, considerable damage could occur!

I can find nothing rattling or loose except the cylinder cowl is a very tight fit against the cylinder.

Any other suggestions?
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Speed Demon
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Mon Jul 20, 2009 11:05 pm

tried to explain pinking to my mrs this way:

if its a noise you can hear are a certain speed or rpm irrespective of throttle position then its just a rattle...

if its a noise at set certain rpm that you can turn on and off by adjusting the throttle or applying the choke then its pinking and you need to do something about it.
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rog60
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Mon Jul 20, 2009 11:14 pm

Speed Demon wrote:tried to explain pinking to my mrs this way:

if its a noise you can hear are a certain speed or rpm irrespective of throttle position then its just a rattle...

if its a noise at set certain rpm that you can turn on and off by adjusting the throttle or applying the choke then its pinking and you need to do something about it.
Neither, it's a noise I can hear at various throttle settings and engine speeds until engine rpm exceeds 5000 (estimated) rpm. i.e. engine is revving quite high. Also engine starts well, idles evenly and performance does not appear affected at any engine speed. :?: :?: :?:
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rog60
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Mon Jul 20, 2009 11:33 pm

sean brady scooters wrote:thats a good explanation sticky.................... :D
what tickles me is the fact that your missis is even at all remotely interested.............. :lol:
after you explained that to her,did she by chance say..........."ok darling........if you say so..................turn the light off now,cos i,m tired."............ :lol:
Well at least you didn't say the rattle only happens when the missus is in the pillion seat. :D :D :D
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Speed Demon
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Mon Jul 20, 2009 11:53 pm

sean brady scooters wrote:thats a good explanation sticky.................... :D
what tickles me is the fact that your missis is even at all remotely interested.............. :lol:
after you explained that to her,did she by chance say..........."ok darling........if you say so..................turn the light off now,cos i,m tired."............ :lol:
She's more than interested. Her Ts1 which I'd jetted bob-on for full throttle running (flat-out 2-up to Scarborough no probs) seized this year going down a massive hill on the M20 on the way to France.:( Not good, but luckily not serious.

It turns out it was a little lean for part throttle at a certain rpm range on a PWK copy.

Now if she'd have been able to detect pinking it wouldn't have happened, but it was my fault in trying to iron out a spluttery part of the throttle range at the expense of safety. New TS1 motor now installed along with a PHBH30 which I've managed to jet much safer but performing even better, however she's naturally a little nervous now.

A may of mine used to have a pinking repair device for his Vespa. He'd just put his walkman on. I do not suggest this is a sensible thing to do but it worked for him. Occasionally....
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