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Makotosun

CT1-C started! but not for long.

  • SKYDANCER46
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Replied by SKYDANCER46 on topic CT1-C started! but not for long.

Thanks guys! just what i needed to see. Never seen one so thin with a stock bore? I am going to measure the bore tomorrow and see what oversize piston i can go with. Most likely 3rd or 4th. Never know though. 

1970 DT250C
01 Aug 2021 17:08 #11

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Replied by MarkT on topic CT1-C started! but not for long.

Look at the design.  The transfer ports are part of the cast iron cylinder which allows them to make the inner wall of transfer thin like that and transfer ports bigger.

Wouldn't work if transfers were in the aluminum like most cylinders we see.
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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01 Aug 2021 17:37 #12

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Replied by mtalley11 on topic CT1-C started! but not for long.

I happened to have a used spare CT1 jug lying around was going to put on my AT1. Measures a tad over 66 at bore. Skirts appear thin like yours but (to me) look to be cast that way on purpose. Port walls get quickly thicker to łike 1.5 mm. Crank bearing play would be a problem but blown crank seals are more common. I might be tempted to replace seals and see how she runs before cracking the case but that's just how I roll. I often make problems for myself when none really exist. I've starting dumbing down and making sure if it ain't broke, I don't fix it. YRMV
 

 
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Last edit: 01 Aug 2021 21:22 by mtalley11.
01 Aug 2021 21:16 #13

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Replied by shyted on topic CT1-C started! but not for long.

If the bore on my bike was in that state, personally i wouldn't think twice about stripping the motor. If there's rust in the bore i would ( right or wrong ) assume its on the crank.
The hardest thing about that motor is holding the gears in place when your rebuilding it.
Knowledge is power, therefore download the manual free of charge from here in the Tech section,
Read it through. 
You have loads of help at this site. You have a good access to parts in the US. Better than here.
All you need then is the tools and some sealer. Bobs yer uncle.
My CT3 looked like it came from the bottom of the sea. Inside and out. It's even got the wrong crank in and an AT 1 right hand crank case which i had to open up on at the barrel mouth with a rotary file. 
Imagine how pissed off you'll be if you replace the seals and then in 10 mile it starts vibrating it's knackers off. Crank pin shot at with rust. 
 
02 Aug 2021 11:38 #14

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Replied by SKYDANCER46 on topic CT1-C started! but not for long.

Mtalley11,

Any play in crank bearings scares me. Especially as much as this one has.
Also measured the cylinder today. 

66.065  top        2.601
66.103  center   2.6025
66.090  bottom  2.602

stock piston came out of the bike measures: 
65.54  top
65.86  center
65.90  3/8 up from bottom

Going to need a bore job for sure.

Shyted,

Crank and lower end looks clean despite the rust in the upper half of the cylinder. As for splitting the cases, I've done many of them and have all the tools. See my avatar picture. That was the 73 RT3 engine i completely went thru and rebuilt including installing a NOS rod kit. The reason i was hoping not to was because i am fixing this bike for the original owner and i know from experience it's going to get expensive when i get in there and do a total rebuild. I won't pull it apart and just replace the bearings and seals for the crank. The rest of the bike needs a lot of work too so it now might go over the guys budget. That's my concern. 

Time to shop for a oversize piston and rings set and a good machine shop. My guy i used to use is retired now. 



 

1970 DT250C
Last edit: 02 Aug 2021 17:28 by SKYDANCER46.
02 Aug 2021 17:18 #15

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Replied by RT325 on topic CT1-C started! but not for long.

If ya only going to replace the crank seal behind the mag & that bearing has play--eyeball it closely with seal out & look at the cage to be sure its in one piece as had one break up but on a 100cc. See if all the play is in the bearing or if the bearing is spinning on the crank. If it's 'that', well, better 'that' than having bearing fall apart if you want to keep running it. Those 6205 bearings didn't come loose & turn like smaller motors generally.
02 Aug 2021 17:34 #16

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Replied by mtalley11 on topic CT1-C started! but not for long.

Sounds like you have a good handle on what needs to be done. Good luck with it! Looking forward to hearing how it works out.
02 Aug 2021 17:45 #17

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Replied by MarkT on topic CT1-C started! but not for long.

Yes, might have spun the crank in the bearing.  I've seen a few do that.  Not sure why.
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
02 Aug 2021 19:20 #18

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Replied by SKYDANCER46 on topic CT1-C started! but not for long.

RT325, 

i will carefully check the bearing this weekend when i pull the flywheel, magneto assy and seal before deciding to pull the engine. 

Mtalley11,

I am sure your right that it would run decent with a new top end and new crank seals. Has anyone run there bike with known play in the crank bearing and not worry about it?

 

1970 DT250C
03 Aug 2021 14:41 #19

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Replied by RT325 on topic CT1-C started! but not for long.

Yep i've go my little 100 LS3 running with considerable play. "ok, i'm standing in the badboy corner". One of my kids wanted it to use for work in the summer. Still going well but sure not ideal. I know the shaft has spun & worn in the left bearing, so not the bearing coming to bits & will fix it oneday 'when i get it back'. Could feel the rumble vibe just off idle which is what made me go looking. Mate '80 something' owned it & gave it to me. Mint bike he rode to work for many years i guess very slowly getting worse once it started slipping. At work with this problem we tried getting locktite to flow down in between bearing & shaft with limited success by laying the bike over & seal out.
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03 Aug 2021 15:16 #20

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