"Doing it Right" or "How to Build a Functional Café Racer"

[datadavid]

Re: "Doing it Right" or "How to Build a Functional Café Racer"

That is decided by measuring your cylinder bores, quintin.
You look for width and out-of-round with a 2-point micrometer.

 

[Quintin Snell]

I was having compression issues too, but much better now, sitting around 8.6 now, number 2 is around 8.8, dont remember what it was before, but bad...

 

[Sonreir]

How are you arriving at those numbers?

 

[Quintin Snell]

Im assuming bar, thats what the mechanic said (not the one who did the rebore, and i did the rebuild myself) i dunno how trustworthy he is though, when he did my carbs, they were worse than before he started. The guy who actually fixed my carbs also said compression was good though, and also called the previous guy an idiot

 

[Sonreir]

Compression ratio is a calculated, not measured, value.

The compression you measure is in PSI.

 

[Quintin Snell]

South africa, we work in metric, he measured it via the spark plug holes

 

[datadavid]

Re: "Doing it Right" or "How to Build a Functional Café Racer"

We do in sweden as well quintin, thing is psi i a finer scale.. my comp gauge is in both psi and bar.
My uncle used to live in south africa, he had a cobra replica built there, and started a bobber build with revtech engine. When we got the stuff up here me and my father just stared in disbelief at the horrible stuff that was done to the machines. Imagine a 7 liter v8 hanging in one (!!!) Bolt.
Gas tank was completely loose, wiring was an abomination.
In the engine they tried using metric bolts in inch threads, and there was no correct ISO standards on any bolts..
So.. i dont give much for south africas builders..

 

[Quintin Snell]

I agree, there are some really sloppy and bad techs, but some of us take pride in our work. (Im no tech, just an enthusiast, but i did successfully get my totalled bike back on the road in near showroom condition with very little help) If i was to build a bike to sell, i would take the same care as i did on my suzuki. Forcing imperial and metric together is unforgivable, if it feels too tight, then it is, re check and tap or cut if nessecary. Better still, get the right part... its difficult, but not impossible to find imperal parts in south africa, especially with the internet!

 

[datadavid]

Yea of course I've seen some superior restorations as well! I remember some guy restoring a couple of bikes from the 20's, they were awesome..
One was an enfield v-twin if i recall correctly. Absolutely beautiful.

 

[Quintin Snell]

Important thing is i eventually found a mechie i can trust, and after over a year of fighting my carbs, the suzuki is running like she should, even has a crazy power band which wasnt there before... much happiness. Now i have found this forum with so much info on it, my cx can't be anything other than beautiful. (Unless i build like a monkey...)

 

[Sonreir]

OK.. if that's BAR and not ratios, that makes more sense.

Still... that's a very low reading. You want about 10.5 to 11.5 BAR on a fresh engine. Anything below 10 is definitely a problem.

 

[datadavid]

Re: "Doing it Right" or "How to Build a Functional Café Racer"

Maybe engine was cold with dry barrels?

 

[Sonreir]

Possible. But I would hope a mechanic would know better than to do that (proving there were other options).

 

[Quintin Snell]

Im assuming bar, thats what the mechanic said (not the one who did the rebore, and i did the rebuild myself) i dunno how trustworthy he is though, when he did my carbs, they were worse than before he started. The guy who actually fixed my carbs also said compression was good though, and also called the previous guy an idiot

I refer to this... i dont know how good the first guy was, but he gets a vote of no confidence from me, he wont be working on my bikes again... sad thing is, it is a mate of mine's shop, and i think his choice of mechanic is a liability, not an asset. Ive told him as much. Apparently they get a lot of returns from unhappy customers, and are starting to get a bad reputation.

 

[datadavid]

Re: "Doing it Right" or "How to Build a Functional Café Racer"

And if its rebuilt and not yet run in, comp will probable lower than with seated rings

 

[Quintin Snell]

Rebore, new pistons and rings, barely run in, maybe about 600 miles since open heart surgery, evertyhing is still shiny and new...

 

[Sonreir]

Everything should have been bedded in within the first 20 miles or so, assuming you've run it hard.

 

[Quintin Snell]

Nope, no hard riding, all gentle 300rpm region. Ive been told by a lot of people who know more than me that i have to take it easy during run in or i will ruin the rebore and new rings. i was also having carb nightmares, and still charging issues, but carbs are finally done, and once the charging fault is done, i can finally get some actual performance out of her.

 

[stroker crazy]

Ive been told by a lot of people who know more than me that i have to take it easy during run in or i will ruin the rebore and new rings.

It ain't necessarily so!

Crazy

 

[Sonreir]

Nope, no hard riding, all gentle 300rpm region. Ive been told by a lot of people who know more than me that i have to take it easy during run in or i will ruin the rebore and new rings. i was also having carb nightmares, and still charging issues, but carbs are finally done, and once the charging fault is done, i can finally get some actual performance out of her.

I don't subscribe to that theory. I believe the exact opposite, actually.

If you don't run it hard in the few 20 miles or so, the rings will never seat as well as they could have.