Here are some close ups of the WTF 4U0 cylinder exhaust ports ...
What is the deal with these notches?
(https://i.ibb.co/Mkr0LYX/FF159-CEA-0793-495-A-9-A39-F728-FC22-E653.jpg)
(https://i.ibb.co/6cK3Hbm/EF86-FF0-B-2-DC5-4-E4-B-A23-E-980-A99-CA5804.jpg)
(https://i.ibb.co/Vq5vBZj/5-AE9-BC86-00-C4-4163-AC41-D21388-C2-EB5-C.jpg)
(https://i.ibb.co/GchD0p7/3249-FD42-7-FF8-4-D6-E-88-D7-8-F52-D32-B4198.jpg)
(https://i.ibb.co/XS20YXd/B8-AD7-F36-5581-408-D-AEEB-003-C2-EFB804-C.jpg)
(https://i.ibb.co/gtMf0qn/0-C56-BDCA-14-FD-409-E-A2-BC-A1-EA6-EB491-FE.jpg)
Could be a quasi compression bypass. The rd400 has a hole above the exhaust port with a little tunnel leading into the exhaust for compression release. They are blocked off permanently on my rd. ?? Maybe :umm:
(http://www.rd350lc.net/Cylindre4L0.jpg)
Now the question is ... what effect will these notches have on performance?
Looks to be a short lived experiment, as I don't believe 2V0 cyls have these notches, and they only lasted one year on the 4L0.
Since the exhaust ports came up, why is there difference in the exhaust gasket area between the 2 cylinders?
(https://i.ibb.co/5B27x7Z/7031-DE7-A-0-DD2-4804-BF31-18-C38-D07-F3-F1.jpg)
I have actually never seen a set of '0' stamped early barrels. I have had 15 sets and they were all the '1' or '2'. From what I recall the early ones were prone to some issues. I honestly can't remember what but I remember not wanting them. I noticed that odd portion in your initial pictures.
A couple other things:
-Are those exhaust ports filed on the edges? They look rather sharp and likely to catch a ring. My cylinder guy makes sure to chamfer (right word?) all ports when he bores my barrels.
-Per my original comment before, it really looks like the barrel on the right has had a weld repair in the past. I suspect that is why you have the larger surface area, imperfections and what looks to be either thicker material or a slightly crooked tap to that stud.
Both of the above are a bit hard to tell from looking at pictures.
Quote from: oxford on September 26, 2019, 07:00:40 PM
Since the exhaust ports came up, why is there difference in the exhaust gasket area between the 2 cylinders?
(https://i.ibb.co/5B27x7Z/7031-DE7-A-0-DD2-4804-BF31-18-C38-D07-F3-F1.jpg)
As can be seen in the image I posted, the early cyls have the small exhaust gasket area, then they went to the larger gasket on the 81-82 cylinders
Quote from: motodreams on September 26, 2019, 07:16:01 PM
A couple other things:
-Are those exhaust ports filed on the edges? They look rather sharp and likely to catch a ring. My cylinder guy makes sure to chamfer (right word?) all ports when he bores my barrels.
-Per my original comment before, it really looks like the barrel on the right has had a weld repair in the past. I suspect that is why you have the larger surface area, imperfections and what looks to be either thicker material or a slightly crooked tap to that stud.
Both of the above are a bit hard to tell from looking at pictures.
I see no indication of any welding or repairs, but it does look like the exhaust flange suffered some drop damage when the sleeve was broken 🤦🏻♂️.
(https://i.ibb.co/0cxqPYK/9590-C3-D6-8422-4060-848-B-B294531-E8838.jpg)
I dunno what the heck Chuck did to this cylinder, but he certainly wasn't gentle with it
Put it together and see how it is. Should not make a difference other than sealing exhaust-RTV.
Make some smoke.
JT
Quote from: RdsOnly on September 27, 2019, 08:29:14 PM
Put it together and see how it is. Should not make a difference other than sealing exhaust-RTV.
Make some smoke.
JT
Thx JT. Yes I know. Cosmetic dings only. I always goop up the exhaust with lotsa RTv and let cute overnight at least 🤙
I've always heard 2 different stories about the holes in RD400 cylinders above the exhaust port.
1)Says: The holes are there to cut down surging at cruising speeds. Or
2)Says: They were their to make the engine easier to start by keeping the compression low at kicking rpm. At high rpm, the hole would apparently close fast enough before it could bleed cylinder pressure off to effect performance much.
I don't think in the 350LC that the Kicking compression was an issue the way it might have been in the 400 unless they significantly raised the compression in the LC's.
But I do remember and motodreams might know better that the first LC's were breaking pipes at the flanges right at the cylinder face so maybe these grooves were there to cut down on surging in an attempt to ease the strain on the pipes, I think they tried thicker material in the pipes near the flanges also and eventually found that adding the now common RZ style torque struts under the engine fixed the problem.
Ask on the LC forum about the early pipe breakage and see what they say, I think they changed the ex stud design because of it too? Ed
Yes! Thanks for your insight Ed!
(http://www.rd350lc.net/Pot4L0-8081.JPG)
(http://www.rd350lc.net/pot4LO-8082.jpg)
(http://www.rd350lc.net/TieRod4L0.jpg)
From what I can tell, the first run of 350LC's had the small exhaust gasket/thinner exhaust header, cutouts in the exhaust port roof, and no engine tie bars.
It appears the engine tie bars and exhaust changes were due to problems with the engine twisting in the frame and cracking the exhaust at the manifold. The tie bars held on thru the RZ and TZR/TDR/R1Z (etc) models.
Unfortunately, the UK guys don't seem to know much about the early LC's as I think they were mainly sold in Japan. Mine is a JDM 4U0 model. VIN is 4U0-005761
Those early barrels are a real rarity. In the last 5 years I have sold 20-25 sets of LC barrels and none of them were the early style.
Quote from: motodreams on September 28, 2019, 09:19:57 AM
Those early barrels are a real rarity. In the last 5 years I have sold 20-25 sets of LC barrels and none of them were the early style.
Yeah, the guy I'm getting another set from has piles of them and they are all the new style.