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DT175 mx 1978 Base Gasket Leak?

  • MikeK-uk
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DT175 mx 1978 Base Gasket Leak? was created by MikeK-uk

Good morning all,
First ride after engine rebuild.
And it looks like I have a base gasket leak.
I know there can be leakage from the exhaust joint, but that looks dry to me :-(
Thoughts / suggestions?!
Thanks,
Mike
13 Apr 2024 03:44 #1

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Replied by Tinkicker on topic DT175 mx 1978 Base Gasket Leak?

What makes you think you have a base gasket leak?

You have not given us much to go on other than you think you have one.
13 Apr 2024 03:50 #2

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  • MikeK-uk
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Replied by MikeK-uk on topic DT175 mx 1978 Base Gasket Leak?

Yes - you are right. Didn’t realise photos weren’t posting.
Just joining a photo sharing site so the problem can be seen :-)
13 Apr 2024 04:20 #3

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Replied by MikeK-uk on topic DT175 mx 1978 Base Gasket Leak?

Can you see photos here:

photos.app.goo.gl/FcfC41zzLSKWXa8PA
13 Apr 2024 04:30 #4

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Replied by Brzn on topic DT175 mx 1978 Base Gasket Leak?

The cylinder base gasket leaked on my DT2 last year after I removed the jug and put it back on with a new Yamaha brand base gasket, not using Yamabond. This winter I replaced the gasket, again with a Yamaha brand base gasket and this time using Yamabond #4 on both gasket surfaces. After two rides totalling 30 miles I see no evidence of anymore leaking.
The 2-Stroke oil leaking from my base gasket looked like the Yamaha 2S 2-Stroke oil I use, not what appears to be shown running down onto your transmission.
13 Apr 2024 05:12 #5

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Replied by MikeK-uk on topic DT175 mx 1978 Base Gasket Leak?

Mine is leaking from the front. Oil is black so post combustion I assume. Will get handy with some talc to try to be sure where it is coming from.
Thanks for the tip about yamabond 4.
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13 Apr 2024 05:30 #6

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Replied by Tinkicker on topic DT175 mx 1978 Base Gasket Leak?

I do not think its the base gasket.  I think it is cleaning fluid or oil from the cylinder hold down nuts or studs.

Engine gets hot, trapped oil expands and forces its way out through the gasket.  Seen that loads of times.

I remember in particular, a Volvo D7C that had a head gasket problem in my department.  Oil seeping out from the gasket when the engine got hot. The lad changed the gasket two or three times without result.  In the end I observed him changing the gasket and putting the head on.  He was very liberal with the oil on the bolt threads.  He was dipping the bolts in a jar of oil to speed up the process.
Gasket "leaked".
Told him to change it again, but this time with just a dab of oil on the threads.  No leak.
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Last edit: 13 Apr 2024 06:34 by Tinkicker.
13 Apr 2024 06:33 #7

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  • MikeK-uk
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Replied by MikeK-uk on topic DT175 mx 1978 Base Gasket Leak?

Well that’s a very interesting comment…. Thank you!
Will give it a clean and do a bit more running about before doing anything drastic then.
Thank you… as I have said before, this is a great site!
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13 Apr 2024 06:44 #8

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Replied by Ht1kid on topic DT175 mx 1978 Base Gasket Leak?

I would clean the area and retorque your bolts 
13 Apr 2024 07:42 #9

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Replied by MarkT on topic DT175 mx 1978 Base Gasket Leak?

Talc idea is a great one.  I agree looks like "after combustion" oil. 

I had a 175 that had a similar dark black leak...  it turned out to be coming from a pinhole in the exhaust pipe belly seam, oil was actually dripping from above the reed valve and running forward.

If I remember correctly, it stopped itself once the excess oil from assembly burned out of the pipe.
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
13 Apr 2024 09:46 #10

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