Triumphrat

bushybester

Why why (Delilah) the compression?

Why is it when you think and at the time you are advised that’s available use it?

I used slightly higher compression pistons at the time of doing the motor, any way now the advice is to use lower compression or use original standard compression pistons i.e. 8,5 :1 or 9: 1 this sometime after doing the all the work.

What is recommended? I really don’t want to change the pistons now.

Why is it a bad thing to have higher compression pistons on a standard road bike? Please tell me or convince me to use standard?

BB

mike T150

Due to the rubbish fuel we get now i.e. no lead and low octane, running with a high comp engine tends to give a lot of running problems. The lead additive coupled with a high octane rating made for a more even burn. Most high comp engines tend to ping under load when running with modern fuels and those that have been blended with ethanol bring there own problems. Ethanol eats rubber,plastic and fiberglass, so all those owners of Nortons and BSA's fitted with fiberglass fuel tanks need to be real carefull about the fuel they fill up with. The rest of us just have to replace all the O rings in our carbies.

Monty

When i first got my T140D it had the 7.5:1 comp pistons in, i decided to fit 9:1 because i had trouble keeping up with my mates on modern bikes on the motorway when i was two up and loaded with camping gear, we would travel at speeds of 70-90mph+ and she had no problems doing so.

However i found the 7:1 piston engine to be much sweeter running, more torquey, just not so good on motorways especially with a strong wind against me and loaded, since then i have a '98 Thunderbird for this job so i'm seriously thinking about putting her back to 7:1.

I prefer sweet running and torque, don't get me wrong the 9;1 have been fine, just a bit more vibration and i needed to keep an eye on the cylinder head gasket for leaks.

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Just remember Gramps!, motorcycles are meant to remind you of your youth, when you last remember being happy, so at least try to relive some of that memory.

bushybester

Yep, Thanks for the input.

I would still like more options. I have 11: 1 piston bored 80 thou. Noting that the bike will mainly be a show bike and ridden very occasionally, for all that trouble, keep them as is? Or change.

What about a thicker head gasket? If that’s possible?

jimballard

Have you tried any of the "octane boosters" that are available? One of them might do just enough of the job to make the engine work unnecessary. You might have to try a couple of different brands before you hit the right combination.

Sure beats taking engine apart: Jim

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Jim Ballard

The older I get, the faster I was....until lately!! (Speed IS the fountain of youth)!

Woody1911a1

question ? are you having problems with the way the bike runs ? pinging , knocking , poor performance ? or are you just asking because someone told you you shouldn't be running that high of compression ?

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If you love it , let it go . If it comes back to you , you've highsided ;-)

bushybester

No problems, yet it was rebuilt some years ago and only gets started every now and then. I have striped the side covers and taken the head off to clean and polished up.

The guy who is arranging some of the work, who is one of the main racing boffins in NZ, says the bike work / run whatever properly.

Now I don’t know what to do.

BB

Woody1911a1

can't see what the problem is . a bike that's been built to be shown and not ridden , but runs fine according to your tuner .

only problem i see is that the bike's not being ridden

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If you love it , let it go . If it comes back to you , you've highsided ;-)