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Post by tony2stroke on Mar 14, 2024 20:45:53 GMT 1
I would think that the same as the RDLC small windows on early, then larger windows on later models after further development.
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Post by tony2stroke on Mar 14, 2024 21:28:20 GMT 1
Down load the Mitaka piston dimensions table, sorry I don't have a link, but that is very useful in deciding what pistons fit what.
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Post by tony2stroke on Mar 14, 2024 21:50:43 GMT 1
So more research shows 2A7 for DT175E 1977 parts list, then 2K4 for DT175MX 1978 parts list, then 2X2 for 1979 parts list. Not sure where the 2N5 they list together 2N5/2A7 comes in now We now know 1977 is the year of your 2A7 piston, now that is sure, but they are all the same size, the bore and stroke is the same, so all pistons will work, and the bigger the window, the better
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amcq46
L plate rider.
Posts: 41
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Post by amcq46 on Mar 14, 2024 22:46:03 GMT 1
Thanks Tony, that is great info, and better than I found so far.
So next question is what brands of aftermarket piston are well rated and what to avoid?
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Post by 4l04ever on Mar 14, 2024 22:52:11 GMT 1
Try to check the ring pin locations, just in case they are different.
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amcq46
L plate rider.
Posts: 41
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Post by amcq46 on Mar 14, 2024 23:03:21 GMT 1
Try to check the ring pin locations, just in case they are different. That dimension is on the mataka chart, so I can check that tomorrow
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amcq46
L plate rider.
Posts: 41
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Post by amcq46 on Mar 15, 2024 17:24:49 GMT 1
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Post by dusty350 on Mar 16, 2024 9:12:22 GMT 1
I hope you put the right side crank seal on the right way round (castellations face the bearing) before putting it back together
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amcq46
L plate rider.
Posts: 41
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Post by amcq46 on Mar 16, 2024 9:33:11 GMT 1
I hope you put the right side crank seal on the right way round (castellations face the bearing) before putting it back together Oh shit, I put it back the same as I found it, castellations out. May as well take it apart again š«
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Post by dusty350 on Mar 16, 2024 9:44:45 GMT 1
It's not uncommon to find them the wrong way round when stripping engines. The 350Lc parts fiche from Yamaha show it the wrong way round ! The 400E and C fiches show it correctly though. The castellations always face into the engine/crank bearing
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amcq46
L plate rider.
Posts: 41
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Post by amcq46 on Mar 16, 2024 15:02:56 GMT 1
Thanks for that info dusty350, so this isnāt the only engine with the seal the wrong way round. But that has got me wondering what the effect on the sealing is going to be with it the wrong way round, and can I wait till the next time i have to strip it down for a broken piston before I correctly instal it? Which I am guessing wont be too long a wait ;( Obviously the seal on this side has to be an oil seal in one direction and an air pressure (positive and negative) in the other direction. So both sides have to seal, even if the air side is always the more challenging due to it being a gas vs a liquid, but the lip looks fairly symmetrical, so do I run it for the 1st race as it is and fix it later? Whatās the collective thoughts on this?
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Post by dusty350 on Mar 17, 2024 11:58:21 GMT 1
First off, are the crank seals new Yamaha ? Seals dont like long periods of inactivity, and if the bike had stood for a long time without use I would be changing them as a matter of course. It goes without saying that you cant beat genuine Yamaha seals - crank especially. I've stripped a few engines where the seal had previously been fitted the wrong way round. It doesn't help that a Yamaha parts fiche shows it the wrong way round, and I have a Haynes manual for the later model Powervalves that show it the wrong way round in a diagram , although the text says you must face the castellations inwards, so if you look at the pics and not the text, you could easily fit it wrong if you had no prior experience. As I understand it, the castellations are there to form an "additional method of location" (Haynes). Yamaha obviously deemed it necessary to add them to the seal, so that's how I fit them. I have no experience of what happens if they are the wrong way round, but potential air leaks can be catastrophic on 2 stroke engines so I wouldn't risk it. I seized a 400e engine at 95mph on the M25 years ago, and it wrecked it completely - cases, barrels and head totally fubar'd Given the cost and rarity of aircooled parts now, I would make absolutely sure the engine I start with is as good as it can be to give you a fighting chance
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amcq46
L plate rider.
Posts: 41
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Post by amcq46 on Mar 17, 2024 18:06:30 GMT 1
Thanks dusty. I am assured the crank and seals were redone in the last couple of years when the last owner thought he was going to recommission the bike, before the project all stalled again.
I will order some new ones and get it apart again
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Post by dusty350 on Mar 18, 2024 7:50:49 GMT 1
That's a wise move I think. The other thing to consider is that a broken piston like you have suffered would have had lots of smaller bits of ali flying around the crankcase. Who knows if damage was done to the seals ? I was emptying bits of piston out of my downpipe when mine went bang, so plan for worst case scenario when it comes to crank seals
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amcq46
L plate rider.
Posts: 41
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Post by amcq46 on Mar 18, 2024 10:06:15 GMT 1
I have some genuine Yamaha seals coming from PJME, so the engine will be back out later today.
Still waiting for Harry to return from Thailand before final decision on pistons, but what is the consensus opinion on brands like Mitaka?
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Post by dusty350 on Mar 18, 2024 12:10:04 GMT 1
Japanese manufactured Mitaka are fine - it's what most guys are running around with post rebore. Paul at PJME is the guy to speak to - a real font of knowledge, as is Dave - Muttsnuts. You wont go wrong with their advice
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amcq46
L plate rider.
Posts: 41
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Post by amcq46 on Mar 18, 2024 20:30:35 GMT 1
Back in bits again waiting for the new seals As I have a few days to wait i had a more detailed look at the crankcases. I had spotted that there are a couple of the M6 crankcase threads near the back of the gearbox are starting to fail, so I will drill and helicoil them. More interestingly, I also noticed wearmarks from the rotation of crank on the inside of the cases, more investigation showed that the crank has been welded up at the big ends, which is a good thing for a tuned engineā¦. Except they hadnāt bothered to grind back the welds, so that was what had been touching the cases. so I masked up all the bearings and ground the welds back, then washed it all again. also of note is that one big end is hollow and the other is solid, so the cranks are obviously a mix and match of parts from various generations of RD400. Not ideal for balance, but it will have to do!
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amcq46
L plate rider.
Posts: 41
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Post by amcq46 on Apr 29, 2024 7:44:16 GMT 1
Rebuild is started. Phase 1 : A) get the crank rebuilt with new rods, all new brgs, labyrinth seal, trued up then welded B) get the barrels bored out to 2nd oversize, C) cut windows in the back of the pistons to suit the boost port. I would then collect these parts, rebuild the bottom end , put it in the frame, chain on, carbs on, ignition on etc and take the whole bike back for phase 2. Phase 2: A) reprofile the combustion chamber in the heads to suit the new piston curve B) set the squish C) cut up the expansion pipes and lengthen them by making them cross over, making all the shapes so they fit the frame and avoid the foot controls D) get it started and time up the ignition and get some heat cycles on the engine. Harry the engine tuner goes off to Thailand (for 3 months) in 4 weeks time, so I had the chase him to get my engine phase 1 work done, as I will only have 5 days available before he goes away to get phase 2 done. He said he would have the bits done for me to collect Saturday, but the crankshaft fought him for 3 days as it is getting old and sloppy from being taken apart too often in the past. Getting it to run true took him till Friday night so when i arrived we still had to do the barrels and pistons. While the boring was going on, we checked the crank on the bottom cases and noticed that the new main bearing had much bigger locating pegs and they were in a slightly different position too. So we had to cut new locations into the cases to suit, then wash it all again for assembly. With the crank now in, I put the gear clusters back in, added gasket compound to the mating faces and bolted them together. Once the bores were cut to the new size we dry fitted them with the piston (no rings) and new .5mm base gaskets to check the deck height and port timings on each side to see if they are matched. Harry wasnāt happy with one exhaust port higher than the other and some variations in the transfers, so he scribed a line where he wanted them to be and got his porting tools out to cut them to the new height and shape. Then he started the honeing process to get the piston clearance up to 0.0025ā and a good surface finish for the rings to bed to. This should have been easy but the large ports keep catching the edge of the stones and breaking them off the tool holder, so about 2 hr later we have the clearance right on both barrels!!!!!!!!! It has taken us 9hrs to get to this point and we still havenāt cut the piston windows in! so that just puts a bit more work onto the phase 2 visit. Some photos The crank ready to assemble Crank now running true The Boring bitā¦. Checking the deck height Modding the transfer ports Compare to some std rd400 barrels One of Harryās scooter builds
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amcq46
L plate rider.
Posts: 41
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Post by amcq46 on Apr 29, 2024 8:03:26 GMT 1
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Post by steve63 on Apr 29, 2024 13:01:54 GMT 1
Great photos. It's fun on any bike. What did the KTM do? I used to do a few of the run what you brungs at the Melbourne New York Drag Strip on my YPVS or LC back in the 80's. Started chatting to a guy at the Withernsea bike night last Thursday who was fishing off the wall and he was telling me he races a CBR600 at Melboune now but it'd down to 1/8 of a mile from the 1/4 when i used to go. He said they are fund raising to get it back to a 1/4. It used to be a couple of quid entry and 50p a run back in 1987 . I once went on my GSXR1100H but got knocked off by a car on the way there so never got to run that one.
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amcq46
L plate rider.
Posts: 41
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Post by amcq46 on Apr 29, 2024 13:10:37 GMT 1
Great photos. It's fun on any bike. What did the KTM do? I used to do a few of the run what you brungs at the Melbourne New York Drag Strip on my YPVS or LC back in the 80's. Started chatting to a guy at the Withernsea bike night last Thursday who was fishing off the wall and he was telling me he races a CBR600 at Melboune now but it'd down to 1/8 of a mile from the 1/4 when i used to go. He said they are fund raising to get it back to a 1/4. It used to be a couple of quid entry and 50p a run back in 1987 . I once went on my GSXR1100H but got knocked off by a car on the way there so never got to run that one. I got down to 11.6s and 120mph on the KTM, but there was a 20mph headwind to contend with
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Post by steve63 on Apr 30, 2024 13:01:48 GMT 1
Great photos. It's fun on any bike. What did the KTM do? I used to do a few of the run what you brungs at the Melbourne New York Drag Strip on my YPVS or LC back in the 80's. Started chatting to a guy at the Withernsea bike night last Thursday who was fishing off the wall and he was telling me he races a CBR600 at Melboune now but it'd down to 1/8 of a mile from the 1/4 when i used to go. He said they are fund raising to get it back to a 1/4. It used to be a couple of quid entry and 50p a run back in 1987 . I once went on my GSXR1100H but got knocked off by a car on the way there so never got to run that one. I got down to 11.6s and 120mph on the KTM, but there was a 20mph headwind to contend with I'm struggling to remember which bike and engine it was on but I remember my best time was 12.96 on the LC. The highest speed was 101mph but I think the 12.96 was at 97mph. Something like if you arrive there quicker then the speed will be lower? I did a run against a 500LC and he did about 12.5. The LC would drop out of 2nd every few runs and I'd lose a couple of tenths. I ignored it until it did it at maximum revs on the road snapping a con rod and gouging my Stephens barrels. The price of being lazy.
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