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76 DT400 Crankshaft discs?
- Eflrr96
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76 DT400 Crankshaft discs? was created by Eflrr96
Ok! 76 400 crankshaft has four discs approximately 3/4” in diameter and resemble a smooth surface bottle cap. They appear to be peened in with 3 peens per disc.
why are they there? What if they’re not? I assume they carry weight and if not there the thing would shake like M-Fer without them.
any help would be very appreciated!
Erik.
why are they there? What if they’re not? I assume they carry weight and if not there the thing would shake like M-Fer without them.
any help would be very appreciated!
Erik.
I’m either livin’ the dream or dreamin’ of livin’!
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- RT325
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Replied by RT325 on topic 76 DT400 Crankshaft discs?
Here's a pic taken off ebay of a new one for others to look at & comment on.
If there's nothing behind the caps/plugs then i'd probably leave it & don't worry.
But looks like they've gone radical with balancing but i'm no expert in that respect. photos.app.goo.gl/Dr8MDip9GiiPiVZS6
But here's another yamaha older crank think it said YL2 with lead plugs all the way except on pair of holes which makes me wonder it those ones have fallen out & if so i'd be more worried about that than tin cups with nothing behind the cups. Basically--i don't know the correct answer. & my dinners getting cold haha. photos.app.goo.gl/FiE2nvYvfpyrk2SG9
If there's nothing behind the caps/plugs then i'd probably leave it & don't worry.
But looks like they've gone radical with balancing but i'm no expert in that respect. photos.app.goo.gl/Dr8MDip9GiiPiVZS6
But here's another yamaha older crank think it said YL2 with lead plugs all the way except on pair of holes which makes me wonder it those ones have fallen out & if so i'd be more worried about that than tin cups with nothing behind the cups. Basically--i don't know the correct answer. & my dinners getting cold haha. photos.app.goo.gl/FiE2nvYvfpyrk2SG9
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16 Jul 2024 00:37
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- RT325
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Replied by RT325 on topic 76 DT400 Crankshaft discs?
Back a lifetime ago at work when i had an early twin in bits i found the lead weights had come loose. I just peened them up to make them tight but maybe in hindsight i should have re-melted the lead in place to make a good fit. I thought it was a YDS3 but pics on the net don't show that so not sure anymore. Was back in the "60's. I did think being lead it should stay there as must be for balance rather than looks.
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16 Jul 2024 01:25
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Replied by Eflrr96 on topic 76 DT400 Crankshaft discs?
These are definitely steel as I used a magnet to retrieve them.
Since Bill Bune is just down the road from me I’m going to go over there and see if he will do the job.
seems really odd they’d come loose!
Since Bill Bune is just down the road from me I’m going to go over there and see if he will do the job.
seems really odd they’d come loose!
I’m either livin’ the dream or dreamin’ of livin’!
16 Jul 2024 05:13
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- MarkT
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Replied by MarkT on topic 76 DT400 Crankshaft discs?
I always thought they were installed to "stuff" the crank to increase crankcase compression ratio? Early two strokes (like the 125 DKW - Bantam - Hummer variants) benefited greatly from those types of mods...
1970's Yamahas didn't need more crankcase compression, in fact, they might have had too much from what I've read. More modern engines were designed with less. If you can get the plugs back in, great. If not, I'm not sure you'll notice anything if you leave the plugs out.
1970's Yamahas didn't need more crankcase compression, in fact, they might have had too much from what I've read. More modern engines were designed with less. If you can get the plugs back in, great. If not, I'm not sure you'll notice anything if you leave the plugs out.
1963 YG1-T, 1965 MG1-T, Allstate 250, 1970 CT1b, 1971 R5, 1973 AT3MX, 1974 TS400L, 1975 RD350, 1976 DT175C, 1976 Husqvarna 250CR, 1981 DT175G, 1988 DT50, 1990 "Super" DT50, 1991 RT180, 2017 XT250
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16 Jul 2024 06:03
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- Eflrr96
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Replied by Eflrr96 on topic 76 DT400 Crankshaft discs?
Thanks Mark, so what is your take on the weight aspect of these plugs? Do you think it’ll vibrate like crazy without them?
I’m either livin’ the dream or dreamin’ of livin’!
16 Jul 2024 07:05
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Replied by MarkT on topic 76 DT400 Crankshaft discs?
I like your plan of talking to Bill Bune. I don't know what those plugs weigh, I expect they are fairly light. There something called a "balance factor" but a single cylinder can't really be balanced. And a forged piston might weigh significantly more or less than a stock piston and stuff like that is done all the time without any vibration issues.
I feel how true the crank is what makes a big difference in vibration...
I feel how true the crank is what makes a big difference in vibration...
1963 YG1-T, 1965 MG1-T, Allstate 250, 1970 CT1b, 1971 R5, 1973 AT3MX, 1974 TS400L, 1975 RD350, 1976 DT175C, 1976 Husqvarna 250CR, 1981 DT175G, 1988 DT50, 1990 "Super" DT50, 1991 RT180, 2017 XT250
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16 Jul 2024 14:06
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- RT325
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Replied by RT325 on topic 76 DT400 Crankshaft discs?
Mark mentioned Bantam--Bsa Bantam--my Dads one I was thrashing around about age 11 & talking the crank stuffing plates. Full size plates crimped into the side of the crank which came loose & when I shut it down the plates kept spinning for a short time. I had no idea what was going on until I had it apart one day haha. Sorry, a bit off case & reminiscing back to about 1957 haha.
The following user(s) Liked this Post: MarkT, Snglsmkr, Schu, Ht1kid, Eflrr96
16 Jul 2024 14:45
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- Eflrr96
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Replied by Eflrr96 on topic 76 DT400 Crankshaft discs?
Thanks Mark and RT, I talked to Josh @ Bill Bune, he said, and I quote, "Run it"! Said it wouldn't make a difference.
So now, on to 76 DT400 #2! LOL! Found one in my "back yard" yesterday! DT400 #1 is running great!
So now, on to 76 DT400 #2! LOL! Found one in my "back yard" yesterday! DT400 #1 is running great!
I’m either livin’ the dream or dreamin’ of livin’!
The following user(s) Liked this Post: Snglsmkr, Sneezles61
16 Jul 2024 15:08
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