jimmyg
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Posts: 232
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Post by jimmyg on Apr 2, 2023 20:42:42 GMT 1
Hi guys
My brother has just had his barrels back from having some work done on them and the inlet and exhaust ports are chamfered but none of the transfer ports are, what are your thoughts on this?
Cheers jimmy
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Post by crogthomas on Apr 3, 2023 21:01:13 GMT 1
The exhaust port is much wider than the transfers, so generally the chamfer/radius needs to be much more generous to guide the piston ring back into place. Is is possible that the transfers are chamfered, just not as obviously?
The inlet doesn't need to be chamfered, since the rings don't pass over it, but it does help airflow a little.
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jimmyg
Drag-strip hero
Posts: 232
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Post by jimmyg on Apr 3, 2023 22:17:51 GMT 1
No definitely no chamfering at all on the transfer ports
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Post by crogthomas on Apr 5, 2023 15:23:22 GMT 1
If nothing at all has been done then it might be worth doing so.
But it's usual just to do enough to brake the burrs off the edges of transfer ports, a really minimal amount. It helps prevent air going back into them.
Was it done by someone reputable, and what did you ask them to do? Just a re-bore, or porting too?
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Post by JonW on Apr 6, 2023 13:54:44 GMT 1
Chamfering takes little time and is easy enough to do, no harm in doing it. Thats rule I was taught.
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Post by jon on Apr 6, 2023 18:25:49 GMT 1
Funny subject. I phoned Ron Fahron about getting my 250LC barrels converted to 370cc. He is a firm believer in not chamfering the ports.
Jon
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Post by Tobyjugs on Apr 6, 2023 19:21:12 GMT 1
That's why I find tuning so interesting. I compare tuners to cooks.
They all use different ingredients to make a great tasting cake.
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Post by jon on Apr 6, 2023 19:44:37 GMT 1
That's why I find tuning so interesting. I compare tuners to cooks. They all use different ingredients to make a great tasting cake. He went on about how Yamaha tuners of race bikes back in the day did the same. He said it improves flow. I trust him implicitly and although it’s against all my previous thinking I’ll leave his barrels as he recommends. Another tuner I trust implicitly is Bob Farnham. When you go into the back story you’ll know why. He’s done a lovely looking tune that doesn’t look OTT, but chamfered all the ports heavily. As said different chefs! Jon |
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Post by Tobyjugs on Apr 6, 2023 19:53:42 GMT 1
I've got a pair of Bob's tuned cylinders. He really had a steady hand as the look absolutely symmetrical.
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Post by reedpete on Apr 6, 2023 20:22:45 GMT 1
Got to be careful with the semantics of what ‘chamfer’ means….. as honed the port edges are sharp enough to cut your finger… but it takes almost nothing to soften that which I think all would say is universally essential … but a large chamfer will definitely effect the port discharge coefficient and flow directions. Application could also be a consideration… Road or race… but if ring life compromise on a race engine is a sacrifice worth making if it yields any power gain… but fast road tune needs to do more than ten times the miles of a race engine..
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jimmyg
Drag-strip hero
Posts: 232
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Post by jimmyg on Apr 6, 2023 20:39:48 GMT 1
That's why I find tuning so interesting. I compare tuners to cooks. They all use different ingredients to make a great tasting cake. He went on about how Yamaha tuners of race bikes back in the day did the same. He said it improves flow. I trust him implicitly and although it’s against all my previous thinking I’ll leave his barrels as he recommends. Another tuner I trust implicitly is Bob Farnham. When you go into the back story you’ll know why. He’s done a lovely looking tune that doesn’t look OTT, but chamfered all the ports heavily. As said different chefs! Jon It’s a Fahron 370 conversion, and like Jon says it gos against everything I have ever been told befor so thought I would ask others opinions Cheers Jimmy |
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Post by steve63 on Apr 6, 2023 21:33:42 GMT 1
A friend of ours had an X7 re-bored and it sounded awful when he brought it around. We stripped the top end off and and had a good look at the work. None of the ports had been chamfered so we dragged out the needle files and got to work. It's quite a long tedious job. When we put it back together and started it up again it was lovely and quiet. I've never known barrels to come back from boring with the ports already chamfered but then I've not seen any done by a tuner just engineering places. I just think it's too laborious for them to be bothered with is my opinion. In my experience if it's easier NOT to do something then that's the way things will lean. Personally I could never build a top end up without doing it. Has anyone ever seen a new as in standard size cylinder with the ports not chamfered? In fact I think it gives chamfering details in some of the genuine workshop manuals I have (Yamaha YZ and Suzuki RGV) but I could be dreaming that. The rings would wear off the edges of the ports in time eventually but that would be at the expense of the rings. It would save the time and effort of doing it though if that's important to you. My guess at the difference in power if there was any between chamfered and non-chamfered ports is 0.1hp  or about the same as farting while going for a top speed run. Then again I am very old and cynical. |
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Post by andy748 on Apr 6, 2023 22:58:25 GMT 1
My last rebore at Armstrongs in Newcastle all ports were chamfered, he tuned a set of Banshee barrels i've got and again all chamfered, they've been around longer than i can remember, proper old school. Andy.
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Post by JonW on Apr 7, 2023 2:17:51 GMT 1
A friend of ours had an X7 re-bored and it sounded awful when he brought it around. We stripped the top end off and and had a good look at the work. None of the ports had been chamfered so we dragged out the needle files and got to work. It's quite a long tedious job. When we put it back together and started it up again it was lovely and quiet. I've never known barrels to come back from boring with the ports already chamfered but then I've not seen any done by a tuner just engineering places. I just think it's too laborious for them to be bothered with is my opinion. In my experience if it's easier NOT to do something then that's the way things will lean. Personally I could never build a top end up without doing it. Has anyone ever seen a new as in standard size cylinder with the ports not chamfered? In fact I think it gives chamfering details in some of the genuine workshop manuals I have (Yamaha YZ and Suzuki RGV) but I could be dreaming that. The rings would wear off the edges of the ports in time eventually but that would be at the expense of the rings. It would save the time and effort of doing it though if that's important to you. My guess at the difference in power if there was any between chamfered and non-chamfered ports is 0.1hp or about the same as farting while going for a top speed run. Then again I am very old and cynical. I agree with what Steve says and that in recent years most rebores Ive had done come back with no chamfering. I think its cos most of the guys doing it are 4 stroke guys and dont know/care about ports and of course time is money, so they dont want to do anything extra. Id like to think that extra cost = better service and this kind of work done, but the guy in the office isnt the one doing the work in many places and that means you get the least work done for your money oftentimes sadly. |
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Post by steve63 on Apr 10, 2023 14:11:33 GMT 1
We've had a KX65 & 85. And a YZ125 and 250. These are race machines producing more hp per cc than any LC and they had/have chamfered port edges from the factory.
The general rule is 20 hours running until a change of ring. Approaching 20 you can feel the compression is down a bit and that's with port chamfering. What would it be like without it?
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or about the same as farting while going for a top speed run. Then again I am very old and cynical.