my cast iron barrel 175

[code][img][/img] so this shows my port timing in my barrel 180cc ( figures input at the top) im assuming that the duration of the exhaust port is out of sync with the transfer port timings acording to blair/jennings and that the transfers should be longer duration ( raised ) to fall within the blue transfer band and would be right at around 10000 revs ish. or the exhuast port is way to high and should be lowerd to sync with the transfer ports .any input would be gratefully accepted.. i doubt the engine will rev to 10000 anyway and the crank probably wouldnt be up to scratch either

If I understand your screenshot correctly, the ports are measured from the top of the barrel and the Deck measurement is the distance between the top of the barrel and edge of the piston when its at the top of the stroke.

I checked the angles with another program and the figures agree exactly for the transfers and within 0.1 degrees for the exhaust providing the Deck measurement is subtracted from your figures first.

You have 96 degree exhaust and 59.2 degree transfers (I find it easier to quote half the total opening angle) so yes, the transfers are quite low compared to the exhaust timing. As a consequence your blowdown period is 96 - 59.2 = 36.6 deg which would normally be around 30 to 32 degrees.

So what to do about it ?

You can't raise the barrel to raise the transfers without raising the exhaust which you don't need to be higher and its impractical to lower the exhaust timing without making a liner.

One option would be to try and raise the transfers by grinding the top of the ports. To get the transfer timing up to 62 deg would require raising them by 1.1mm - quite a lot to remove and not an easy job but in the past I have done that sort of thing with little more than an electric drill driving some small ball shaped stones in a flexible shaft.

A long term option of course is to use it as is and plan another barrel.

Have you tried running this engine ? What conrod are you using ?

Mick

thanks for reply mick,yeah when i first embarked on the porting(must be 2 yrs ago) i went for the bigger the better and obviously with my lack of knowledge, its a bit off. having given myself a sharp learning curve since and some helpfull sortware and hints from various posts ive realised that it needs tweeking.should have raised the barrel firstly whipped some off the top and spacer underneath barrel.i do have a deck height and as you say raising the transfers 1.1mm would probably help. i input tom snows porting info ,shown in the posts and it fell within the parameters of the jennings/ blair findings,as shown on the graph although the engine would have needed to get up to around 10,000-10,500 revs to achieve this. i can see why he may be changing his crank size to fall between the the large crankwheel set up and the smaller sized as used on the 125cc bikes. Anyway all is not lost, yet, i do have 2 other standard barrels to play with if i feel the need.. the bike starts up and runs... not had any significant time trying it out as yet every time in the past ive had problems with slipping clutch , gearbox jumping out of gear, big end siezure and bending gearbox shaft when the primary chain decided to let go.... yeah its one of those t&g 125mm conrods, i talked myself into having at the time,mainly because i couldnt source the maico conrod in this country (easier to send back if i orderd wrong) when i first got out on it,it seemed ok,not peeky in fact once it got going it seemed to keep on pulling, nothing to write home about, but i felt the gearing needed to change a bit to get it up there a bit quicker, then when i changed to third it kept jumping out, which hopefully ive cured...so ther you have it. just need to get out on it really to iron out any little bugs and hopefully have somthing that will at least start and finish.

out of interest , what would the ideal heights from the top be for an iron barrel ?

Hello,well in my opinion i think that for the 175 barrel, i should have stayed with the port timings shown in the tuning manual on the home page , at least as a starting point. i always learn the hard way, so i didnt. Really when you consider people, with more years of experiance with this engine and generally have more tuning knowledge, have already encounterd all the problems you could probably come across and ported there barrels to suit. i think mick scutt has written a post within the forum lately about the 175 tuning(tom snow engine bit, i think) which outlines his experiance in the porting dept maybe a look at that would be benificial...all the best

some interesting pictures ive found and had e-mailed to me showing some cast barrel mods..has anyone ever tried these? any success..problems? i can see some of the transfer port stuff is a little dubious,
but the exhaust mods to give more time area by use of a liner being pressed in may help.

Hi Nigel

Hi Nigel just looking through some of the latest posts have some time to kill, reading this one did you resolve this, I see you got some good reply's to this post, out of interest what did you do about the blow down, being a bit on the big side, ? can not imagine how difficult it would be to do on a flexi shaft, take for ever to get right, even then ? not sure how the top edge would be, would like to see it done like this if it can be done, having to lift the transfers without a proper tool grinder must be very difficult, Mick Abbey who made my Exhaust's, also has a porting tool a 90deg right angled special tool made fot the job, he could sort this barrel for you.

Hows the bike comming on,
I always say anything that is not right will or is likley to cause an issue for you in the paddock.

I have these words on laminated paper pinnd up in my shed dad did it in his shed when I was 11 years of age, pefection/maticulas/ it must be right, word in red underneath these were crossed out like a no entry sign these were, "that will do" "close enough" "about right", my dad wrote on a big board in our garage for me, he said that I must fully understand what these mean, if ever wanted to build and race my own engine and Bike, to make it both reliable and powerful. Now having raced for some 18years over a 34 year period, I'm know im still understanding what what these mean.

moving on I'm sure I can not think of a time where I have been so motivated to a hobby as I currently am, this may be because the gains we recently got in hp and troque, from the tinest of change, picked up from "overhearing" listeing intently while pretending to talk to others, on a remark from a conversation between Nick and Trevor at our recent midlands Bantam racing meeting the other week.

Know got your email, the gear change peddle I could not find, but I do have several about, just need to pop down at some point and help me look for it in the shed, or I can show you how I did mine as I had the very same problem, you need a three sided needle file and a thin flat file to resolve the issue for good, did this mod at least 25 years ago, like me it happened in my first few years of racing.

talk soon Derek

Afternoon derek, i never touched the transfer ports, left them as is.. i have however had another barrel machined to remove 4mm off the top. this has got the transfers/exhaust a little closer to the sprinter info contained within this site. made a 4mm alloy spacer to fit under the base of the barrel to compensate..not had chance to use yet as i have been concentrating on the "BAN-TA-RILLA-CVT" engine and also think i still need to get the engine im using to be properly sorted. im not sure which year the alloy barrels came into play but im still a bit suprised that people who frequent this site havnt commented on the photographs of the barrels i posted showing how others have tried to over come the short comings of the original cast barrels.
yeah it seems my lack of preparation is causing me problems .... whod have thought the throttle cable would have mysteriously unattached its self inside the carb second lap of my first practise session last week..swiftly followed by the manifold rubber splitting and the carb consequently falling off.. then my gear linkage giving up leaving me trying to get around the mallory hairpin in third..hence my nickname"LUCKY NIGEL" still it didnt sieze and it didnt rain
(New gear shaft and lever on its way, thanks for looking in your aladins cave anyway... )

I found some Nigel, and a shaft its your if you want to collect them, i found a box full of them all old shorties and a bit used.

thanks fot the info on the practice day, , I was wondering when someone would come on and say how it went, so dammed cold and lots of snow here.

regards DEREK

nobby1 wrote:

This picy is a lambretta 150 barrel that I tuned it produced around 14hp compaired to 6hp STD

Hi Mick
the other exhausts we did(you did does not work as well, but Ihave not had time to ply withit with other settings just yet, perhaps I will use this pipe to do the experiment on the front taper/pipe we spoke about.

hope your well, and I two have a new barrel for my motor a that I need the trasnsfer port windows working on, Can you help ME.
I hear your very busy, if your too busy "put your prices up". !

regards Derek

well, i can see 1400 views of this post and only a couple of replys... come on dont be shy anybody had a go at these mods??  oh yeah, my number one barrel is dead..  it developed a crack around the transfer port after my last outing at mallory test day .. maybe its been the problem all along .although it didnt show up with the pressure test...  

Some ideas made it here on my new barrel.

alloy barrel?, i think this is probably my next step, having one more crack with a cast iron though.. cos im pig headed:

That's what I thought, turned out to be just one more crack, quite literally as it happens