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1978 DT250E - Rust in cylinder question

  • johnste1960
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1978 DT250E - Rust in cylinder question was created by johnste1960

I picked up a 1978 DT250E with about 6000 miles.  Fairly complete (missing side covers) and the bike kicks over.  The guy I bought it from new the history as it was his brothers bike. I was told it was running 2 years ago and they stopped riding it when it lost spark.  

Was tinkering on it the other day and started with a compression test.  When I kicked it over, cylinders seemed odd, sort of dry, metal scraping feeling.  So I pulled the plug and put in a little WD40.   Kicked it over a few times and felt what I considered to be more normal (better) .  Put compression gauge in and kicked it over several times and got a reading of 150 PSI.  I was expecting more like 120-130.  Never really heard of that high of compression especially on a 6000 mile bike.  

When I removed the compression tester,  some of the WD40 was on the  plug insert and when I looked it over, I could see there was a hint of rust color in it.  No big particles or anything,  just colored. rusty .

1) So,  what should be my next step,  Just continue on diagnosing the NO SPARK issue and ultimately giving it a first start when I have that resolved, or do I need to pull the head and look and see the scope of the cylinder.   How much rust can be tolorated?  The bike does not appear overly rusty on the outside, and the gas tank is golden, So I would not expect much more than possibly some surface rust.  Or at least that is what I am hoping.
2) What do you think of the 150 PSI compression?  I am going to retest again, but am sort of thinking the WD40 may have had an impact on the readings.  (I did  not think I overdid the WD40 amount and only put enough in to coat cylinders..  Then kicked it over several times to spread it and coat the cylinder walls)
16 May 2021 12:54 #1

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  • RT325
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Replied by RT325 on topic 1978 DT250E - Rust in cylinder question

Well,--what i do,--so better not recommend it lol, is it kicks over & if nothing binds up i just go ahead & start it & see if it settles down even if it's a little rough feeling to turn over initially from being parked & possibly damp for many years. Likely just the WD40 giving it extras comp, it'll come down to normal once run.
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17 May 2021 03:16 #2

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  • Pete-RT1
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Replied by Pete-RT1 on topic 1978 DT250E - Rust in cylinder question

If you're reluctant to pop the head off, maybe take the exhaust off and have a look at the piston and cylinder through the exhaust port.
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17 May 2021 08:30 #3

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Replied by msavitt on topic 1978 DT250E - Rust in cylinder question

popping the head off takes about a minute and you can even reuse the copper gasket.
and while you seek spark you might want it off anyhow to check timing is one school of thought.

But then again, once you start peeling the onion there's no turning back, so maybe more fun to "go ostrich" and get spark and get it running!
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17 May 2021 09:51 #4

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Replied by Pete-RT1 on topic 1978 DT250E - Rust in cylinder question

I should have said if it was mine I would pop the head off.
As Msavitt says, it takes about a minute to do and you'll certainly get a better idea of what the top end is like.
You can easily anneal and clean the existing gasket.
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17 May 2021 10:36 #5

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  • johnste1960
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Replied by johnste1960 on topic 1978 DT250E - Rust in cylinder question

Thx for the input.   I plan to pull the head off and check it out.
17 May 2021 15:20 #6

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Replied by RT325 on topic 1978 DT250E - Rust in cylinder question

Awww, i wanted to see if it goes.
17 May 2021 19:53 #7

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