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Post by dougw on Dec 22, 2020 10:43:01 GMT 1
Just popped the re-lined barrels on the 350lc and done a quick measure on the main transfer heights .
lh barrel 42.4 one side 43.0 on the other.
rh barrel 42.6 one side 43.6 other.
Exhaust ports are at 28.0
differences seem a lot to me, but will they make a significant difference on a road bike engine ?
I`m not chasing top end on this one, but don't want to build something with significantly less bottom end and worse mid range stutter than standard.
To add confusion, it is running YPVS Microns, it came with those, and I have no standard 4L0 pipes. I do have a set of 31K YPVS exhausts if they would be more suited for stealthy road use.
Opinions please !
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Post by midlifecrisisrd on Dec 22, 2020 12:11:51 GMT 1
I wouldn't worry too much about the transfer heights
As far as I knew the ypvs microns were just the LC ones with longer hangers hanger brackets
Hence why the sat a bit saggy looking on the ypvs
Prepare for a midrange stutter with the crons
Steve
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Post by Tobyjugs on Dec 22, 2020 12:52:30 GMT 1
Have the liners just been pressed in and bored to accept 64mm pistons? if so it might be an idea to give them to a tuner to clean up.
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Post by dougw on Dec 22, 2020 13:25:23 GMT 1
As they are freshly bored I think I will put it together and try to run it in for a few hundred miles and see what its like then.
Get them cleaned up if not happy with it.
Just a little disappointed that the freshly linered barrels need more work.
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Post by 4l04ever on Dec 23, 2020 23:40:27 GMT 1
Whoever did it thinks this is acceptable, which for a standard bike it probably would be okay to use as-is.
A few hp may be lost compared to a well setup engine, which is a shame to waste. The engine may not be quite as smooth as it could be due to uneven power being delivered from each cylinder/side of the engine.
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Post by bare on Dec 24, 2020 4:31:33 GMT 1
Wellll.. Microns are hardly "stealthy" :-)
Relining IS a bodge repair .. Fan Boy claims aside.
But few seem willing to heed this.. my reposte being simply: Enjoy!
Find someone competent (this time) to match the ports /heights.
And Yess..pay yet more to patch the apparently f**ked up relinings.
That said these engines can run well on even wildly missmatched cyls. (cyl Series even)
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Post by bare on Dec 24, 2020 4:34:41 GMT 1
n/t
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Post by 4l04ever on Dec 24, 2020 15:20:09 GMT 1
On a standard engine, transfers should be 43mm to the top of the cylinders and the exhaust ports should be 30mm.
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Post by Tobyjugs on Dec 24, 2020 15:59:13 GMT 1
Problem is if it's been tuned in the past it will cost a lot more time probably money to put back to standard.
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Post by beardy on Dec 24, 2020 16:24:43 GMT 1
I thought relining put it back to standard? Or that’s what I thought it said on the pjme site. I’ll go and have another look.
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Post by beardy on Dec 24, 2020 16:27:42 GMT 1
“Factory porting spec” is what it says. Did you use pjme or someone else?
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Post by Tobyjugs on Dec 24, 2020 16:37:33 GMT 1
Heights are a rough guide you would be better off measuring the port durations
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Post by muttsnuts on Dec 24, 2020 17:45:11 GMT 1
first question should be how you measured them, did you clamp the barrels down to the crank case, or simply have them sat on the crank case ?
Also did you use the exact same thickness base gasket on each side and how did you measure them, what tools did you use and how did you determine when the port was closed
As Tobyjugs has stated, you really need to be measuring the duration of the ports, with the barrels clamped down and using the exact same thickness base gasket and then a method by which you know the ports are closed as its very easy to get that bit wrong.
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Post by dougw on Dec 24, 2020 18:29:05 GMT 1
I measured from the top of the barrel to the piston. I was more concerned with the 1mm of open port when the corresponding port was just opening (same barrel).
I emailed PJME with my measurements and they replied that this is normal when they re line 350 lc barrels.
I was not that concerned with precisely measuring, more to check that the ports where of equal height.
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Post by steve63 on Jan 22, 2021 22:50:18 GMT 1
We bought a second hand KX85 about 12 years ago for £950. Turned out to have a steel liner fitted which used a KX80 piston (1mm smaller to give a couple of oversizes). My lad raced it for a couple of years in the 85 big wheel class against other 85 two strokes and four stroke CRF150's. It was as fast or faster than most of the two strokes and some of the 150's, bit unfair giving them a 65cc advantage I'm not bitter or owt. Anyway it only stopped in one race and that was when the chain snapped. We changed the piston every 20 hours or so as you do. Sold it for £780.
Not a bad bodge really.
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Post by joshready on Feb 9, 2021 12:13:22 GMT 1
Rather than start a new thread i have a few related cylinder Q’s.
The engine to the bike i just attained has had engine work, according to 25 year old receipts. Just whipped the heads off the to look inside.
Its an 81 4lo, 1.25mm oversized. I will do a port map for my records.
Firstly, the B port opens first (good), but almost immediately the C port does too (bad?). Then the A opens a fair bit of a difference later.
Second, the upward angles are A is lightly up and angled to the back half of the bore, B is pointing much more upwards and aiming to where A is aiming. C is even angled higher. This seems ok? Also the barrel looks to benefit from it being raised 1mm more or less, so the bottom of the transfers clear the piston - A is almost flush, but b and c have the piston fouling them.
Third, the B port is tiny, leaving plenty of room to widen the transfers. Would boyeson ports help to feed the B ports, or leave the intake focus on the A ports?
Is this a sign of porting from the early 90’s or is it not required for an engine that runs under 10k rpm?
The intake looks heavily grinded, exhaust port i need to measure but looks narrowish. Heads are stock and more squish than my 2.0mm solder.
Bike has 28mm Vm Mikunis and stock chambers. I have chambers on order, and probably the Kx85 28 pwk’s. Mainly looking at track riding and a little road riding.
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Post by Tobyjugs on Feb 9, 2021 21:44:39 GMT 1
I'm not really a tuner but it sounds like a lot of effort has gone into the tuning of the cylinders.
It is really important to get the charge flowing correctly which sounds good by your description of the angles.
The port durations or height of the ports along with the shape of the exhaust pipe usually govern the effective rpm the engine will run at. For example a bigger port duration usually means higher revving engine.
Squish is important but don't get hung up over it. I have dynoed the same engine with the same set up except for different squish heights. 0.9mm verses 2.0mm the diference was 2hp. Squish helps to keep detonation under control. I noticed a slightly cooler running engine with the 0.9mm squish height.
The uncalculated or geometric compression ratio is more important than squish. Measure this and make sure it's not too high.
There are a few people who can tell you a lot more than me, but we are mostly enthusiasts so replies will be a bit low. Unless you want to know which colour silicone pipe is best. Red or Blue?
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Post by peddrotzr on Feb 9, 2021 22:22:44 GMT 1
Red or Blue 🤔
Blue,
Because it’s a “cool colour” 😎🤪
However I am just a printer and love colours!
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Post by steve h on Feb 10, 2021 0:27:16 GMT 1
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Post by joshready on Feb 10, 2021 6:57:27 GMT 1
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Post by joshready on Feb 11, 2021 2:26:35 GMT 1
Measured ports. Stock except for 2mm taller ex port, B port raised and intake ground some. Heads are stock 20-21cc 13mm squish band.
Do the 4lo engines benefit from a wider B port and Boyeson ports to feed them? Prefer the power in the mid-upper range for track use.
I will be widening the exhaust a little. Hoping cometic do slightly taller base gaskets to get the floors of the transfer perfect with piston at BDC.
Cheers
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Post by dougw on Feb 13, 2021 11:21:36 GMT 1
On an optimally tuned GP standard two stroke with a well designed pipe .the first transfers to open flow LAST due to pressure in the cylinder causing a small amount of flow back down them. They transfer use port stagger to utilise that.
This is one of the facts picked up from one current two stroke tuners posts. (Bucket racing forum, guy called "Wobbly" and Frits Overmars post there)
Whether that applies in any way to a 4L0 I have no idea. He (Wobbly) did raise the opinion recently that a top UK tuners 4L0 cylinders had far too little transfer time area compared to exhaust time area.
Unfortunately, 2T tuning is definitely one of those things that the more I learn the less I realise I know...
Someone elses quote " A two stroke engine is a simple mechanical device that operates in a remarkably complex fashion "
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Post by 4l04ever on Feb 13, 2021 11:43:55 GMT 1
I sell different thickness base gaskets for 4L0 YPVS and Banshee engines. If you need any, let me know.
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Post by joshready on Feb 14, 2021 6:05:03 GMT 1
I sell different thickness base gaskets for 4L0 YPVS and Banshee engines. If you need any, let me know. Great I'll need a slight thicker one. I'll message soon about a couple.of them. |
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Post by joshready on Feb 14, 2021 6:13:43 GMT 1
On an optimally tuned GP standard two stroke with a well designed pipe .the first transfers to open flow LAST due to pressure in the cylinder causing a small amount of flow back down them. They transfer use port stagger to utilise that. This is one of the facts picked up from one current two stroke tuners posts. (Bucket racing forum, guy called "Wobbly" and Frits Overmars post there) Whether that applies in any way to a 4L0 I have no idea. He (Wobbly) did raise the opinion recently that a top UK tuners 4L0 cylinders had far too little transfer time area compared to exhaust time area. Unfortunately, 2T tuning is definitely one of those things that the more I learn the less I realise I know... Someone elses quote " A two stroke engine is a simple mechanical device that operates in a remarkably complex fashion " I'd believe it looking at the transfers as they seem a whole lot less than my cr125 transfers. I will put some Boyeson ports in as well and lower the septum (?) a touch. I do follow that ESE thread. Benefited my cr125. Going of Frits' axial angle formula it looks like the B port is aimed too high, in my example anyway as it's modified. |
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Post by dougw on Feb 14, 2021 11:38:19 GMT 1
Terry Shepherd used to reckon no point in going to 370 on a 4L0 as the transfers became to compromised to shape effectively.
I'd guess that was from a peak hp racing point of view.
Cylinders too close together on a 4L0 to get an optimum transfer port shape.
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Post by dougw on Feb 14, 2021 11:45:02 GMT 1
I have been told lowering the septum gives good results on a 4L0.
Hopefully I'll get some miles on mine in summer and then get the barrels looked at by a guy local to me , trick tuning, for a tidy of the ports and any other work suitable for a " road tune" next winter. Looks like my barrels have already been modified to fit ypvs reed blocks , I've got a set of those and rubbers ready to try.
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Post by bare on Feb 14, 2021 17:56:19 GMT 1
Cylinders too close together on a 4L0 to get an optimum transfer port shape. THAT applies to all Yama 350's as well. Yama was well aware of the problem .. it being the Exact reason that TZ cyls were cast as a monoblock |
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Post by dougw on Feb 16, 2021 18:06:07 GMT 1
Snippet from Kiwi Biker :-
Edit - good example would be a LC 350 Yamaha racebike. Keeping the original scavenging system ( B ports up at 35* ) the best I could do was 66RWHP.
The next version had staggered timings ( A first ) and with modern radial and axial angles , 10mm fatter pipes - 20mm shorter , first dyno run was 77RWHP without adjusting anything.
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Post by Tobyjugs on Feb 16, 2021 18:40:36 GMT 1
That snippet is a bit vague it's like comparing an apple to an orange
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