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Post by db971 on Apr 29, 2014 23:34:53 GMT
Appreciate your comments GeorgeS.
Thinking a bit more about this and surely when these kits are manufactured they are built to a spec with tolerance. Therefore surely the main transfer ports cant be that far out. I plan to take the barrel to a local engineering shop to get them to measure a bit more accurately. I did re measure the main port from tdc and I was getting 113 x2=226 -360= 134 degrees tonight, which I assume might be more in the ballpark??
What is my target measurements for the exhaust & main ports?? for example main 122-126 and exhaust 184-192, squish0.9-1.1mm???
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Post by jeanshorts on Apr 30, 2014 2:00:54 GMT
The kit ports are layed out for a 51mm stroke and I think a 97mm rod (?). When you build it with a 53/105 crank things change. My expirience building a 53/105 with the cast iron polini was getting the transfers down to reasonable was the first limitation. I was able to get them to 124 if memory serves. Point is it's not so straight forward for novices like us and is easy to screw up and there are tricks the experts know as they do it all day. The huge variance in all your measurements makes me think you might best seek out an expert to hire. Surely there are 2 stroke tuners in Scotland.
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Post by db971 on Apr 30, 2014 8:11:44 GMT
Thanks Jeanshort. I am prepared to ship it south. Just want to get this sorted now :-)
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Post by GeorgeS on Apr 30, 2014 9:25:33 GMT
You seem to be getting a lot of variation on your measurements so it's worth just checking that first before anything else. I took a couple of hasty pictures this morning before leaving for work which may help, hopefully there's no reflections of me wearing not much more than an smile on my face... Apologies if you know all this already. You and I are at similar places on our builds with similar parts so I'll blab on while it's fresh in my mind in case it helps. Here's what I'd do, 1. With your barrel bolted down with packer, gaskets etc (so you get an accurate measurement of how the barrel will be when fully fitted) & degree disk fitted I rotate the crank anti-clockwise until the port to be measured is opening (with piston going downwards)& use a feeler gauge for accuracy: 2. I prefer to use a piece of heavy garden wire soldered to a bulldog clip and then move that to the nearest whole number of the degree disk. In this case it was 110 3. I then rotate anti-clock so the piston continues downward, past BDC and up again to the point where again the feeler gauge is pinched as the port closes. I read 300 on the disk, so my timing is 300-110 = 190 Do that for the other ports in your barrel, e.g. the left & right transfer ports. All the best, George.
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Post by db971 on May 6, 2014 21:25:50 GMT
Thanks GeorgeS. I am a fecking donkey.
Ended up starting from the beginning with regards to the measurements as I hadn't fitted the bloody piston rings. So pistons rings installed, engine fixed to bench bracket and started the measurements.
Had the following base spacers installed 0.52mm + 8.1mm = 8.62mm plus the basket gasket 0.5mm = total 9.12mm
Exhaust port measured 183 degrees (checked 5 times) Main port measured 122 degrees (checked left side and right side ports)
Squish was 0.90mm with the 0.5mm copper head gasket fitted.
Any thoughts??
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Post by jeanshorts on May 6, 2014 22:29:35 GMT
What pipe again?
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Post by db971 on May 6, 2014 22:41:33 GMT
Franz pipe
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Post by jeanshorts on May 6, 2014 23:06:09 GMT
So I think you are in range w the blowdown at 30.5. Use the .8 head gasket to get 1.3 squish or add .3 under the cylinder and remeasure timings.
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Post by db971 on May 7, 2014 18:49:14 GMT
Cheers Jeanshorts
Have changed the base spacers to the following 0.78mm + 8.1mm = 8.88mm plus the basket gasket 0.5mm = total 9.38mm
Exhaust port measured 186 degrees Main port measured 124 degrees
Squish was 1,05mm with the 0.5mm copper head gasket fitted. (thought it would have been a bit more. Checked it a number of times)
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Post by GeorgeS on May 7, 2014 19:06:48 GMT
Ah that's good news, your new readings look much better.
I guess you could raise up a little more to get transfers to 125 and then with the barrel bolted down make some marks as to where the top of the exhaust port needs to be. So if you're at 125/187 and you want the exhaust to be 190 you need to rotate the piston up 1.5 degrees and mark it (you'll be adding 1.5 degrees down and 1.5 up adding 3 degrees to 187 to get to 190). Hope that makes sense.
What's the recommended squish for your kit?
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Post by db971 on May 7, 2014 19:39:43 GMT
Cheers GeorgeS.
As far as I know the squish should be 1mm for this kit. Hopefully someone can confirm.
Read back through this post again and I think I should be aiming for 192degrees exhaust timing, with 32 degrees blowdown for the Franz pipe??
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Post by jeanshorts on May 7, 2014 20:37:13 GMT
So that would be 128/192. Make sure that's what is called for. Strikes me as high but I'm a novice so.....
Also that kit is based on a 51 stroke so I'd think you'd want to err on the high side, like 1.3 squish.
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Post by GeorgeS on May 7, 2014 20:54:08 GMT
You wouldn't raise the transfers to 128, just pack up the barrel so they measure in at 125, from there mark on the barrel where 192 degrees would be for the exhaust port & that's your line to open the port to with your dremel.
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Post by jeanshorts on May 7, 2014 21:12:31 GMT
You wouldn't raise the transfers to 128, just pack up the barrel so they measure in at 125, from there mark on the barrel where 192 degrees would be for the exhaust port & that's your line to open the port to with your dremel. That puts blowdown at 33.5. Not sure you want it that high
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Post by db971 on May 7, 2014 21:38:07 GMT
Jeanshorts . The crank is a 53mm stroke,105mm conrod for a rotary valve
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Post by jeanshorts on May 7, 2014 21:48:08 GMT
Jeanshorts . The crank is a 53mm stroke,105mm conrod for a rotary valve Right, you're altering the stroke the kit was intended for. Your compression ratio will be higher, so maybe max out the squish.
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Post by db971 on May 11, 2014 18:05:45 GMT
Any of the experts got any thoughts on this and the setup I have and where I need to be/adjust?
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Post by GeorgeS on May 11, 2014 20:41:23 GMT
I'm no expert, but I'd raise your barrel until your transfers are right (125 or 126 for franz) then mark out what you need to get to around 190-192 for the exhaust, shorten the barrel by whatever is needed to get the squish recommended for your kit.
As for blow-down, do you have much choice? I suppose its just what you end up with when aiming for specifics on transfers & exhaust timing. Measure it & see what you get. Hopefully someone with more knowledge and experience can put us both straight!
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Post by daisyb on May 12, 2014 20:50:07 GMT
Was bored at 3 Sisters on Sat evening so I read through this thread again, firstly read back through the early postings and listen to the advice (re timings and other bits) that Mathias gives you, do not get side tracked. What he doesn't know about SF engines probably isn't worth knowing. As to squish, changing the length of the rod makes no difference to the squish clearance needed. Go with 1mm. Imho 1.5 in a small engine isn't working properly as it's supposed to, I'd run down to .6 or .8 depending on final max rpm, but then I like rebuilding engines!
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Post by daisyb on May 12, 2014 20:50:58 GMT
Post accidentally duplicated
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