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 Post subject: occasionally smokey
PostPosted: Tue Nov 13, 2018 2:51 pm 
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Hi Guys,
I have a sierra with a mk3 g13b that has just been freshly rebuilt with 20thou over pistons. The head was rebuilt by one company we use thru our work 6months earlier, the bottom end was built by another mob that did my mates motor and I gave him the head and cams to set up too.
It has only done 550kms so far but I have noticed it chuffs smoke if I back off down a hill and then jump on the gas. This to me would point directly to valve stem seals but I just thought I would throw the question past you guys to see if anyone has had the same issue. I have now put in a catch can that takes the breather hose from the rocker cover and also the other breather that had the pcv valve into the manifold. I also blocked off the manifold side.(can is then vented) Anyone have any ideas? I'm keen to try everything first before pulling the cams out to swap out the valve stem seals.


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 Post subject: Re: occasionally smokey
PostPosted: Wed Nov 14, 2018 4:04 am 
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Oil rings not yet seated?

I presume you would have put new piston rings in too, so it's quite likely the new rings have not yet bedded in. Bores got a light hone during rebuild?

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 Post subject: Re: occasionally smokey
PostPosted: Wed Nov 14, 2018 11:25 am 
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Engine has new 20thou over pistons so it was bored to match those. The engine builder told me to only do around 500kms of a certain style of driving then dump the oil and it should be fine after that. I have asked the question to him about the smoke but he has just said it was stem seals (as he didn't rebuild the head) and said if it was oil rings it would be doing it constantly.


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 Post subject: Re: occasionally smokey
PostPosted: Fri Nov 16, 2018 6:52 pm 
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Did the stem seals get replaced when the head was rebuilt??

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 Post subject: Re: occasionally smokey
PostPosted: Sat Nov 17, 2018 5:40 am 
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Location: NZ
From my previous mechanic days. Yup valve guide seals.


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 Post subject: Re: occasionally smokey
PostPosted: Sun Nov 18, 2018 6:54 pm 
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The other giveaway for stem seals is smoking at high RPM, and smoke on startup if the engine has previously stopped in a position where the problematic valve was open.

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 Post subject: Re: occasionally smokey
PostPosted: Mon Nov 19, 2018 5:52 am 
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What he just said! Good points.


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 Post subject: Re: occasionally smokey
PostPosted: Mon Nov 19, 2018 3:15 pm 
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Appreciate the responses guys, the stem seals were replaced when the head was rebuilt. The only thing I thought it could be was that they damaged one while fitting it. It doesn't seem to blow smoke when its been idling at the lights and you take off or at high revs its only when you decelerate more than a few seconds and then get back on the gas whether that be at 60km or 100kms. I will keep putting some more kms on the engine and see if it settles as the engine beds in.


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 Post subject: Re: occasionally smokey
PostPosted: Mon Nov 19, 2018 6:39 pm 
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Heavy backoff and roll on causing smoke is a telltale sign of the engine sucking oil from on top.

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 Post subject: Re: occasionally smokey
PostPosted: Wed Nov 21, 2018 4:05 am 
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Pcv valve?


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 Post subject: Re: occasionally smokey
PostPosted: Thu Nov 22, 2018 8:03 pm 
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What colour is the smoke? If it is blackish then it might just be fueling up on overrun and blowing it out when you hit the hammer.

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 Post subject: Re: occasionally smokey
PostPosted: Tue Nov 27, 2018 11:13 am 
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Its a bluey smoke. It does run quite rich because of the chipped ecu but that is more of a black smoke which really only appears when its cold. after it warms up a little that doesn't happen.


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 Post subject: Re: occasionally smokey
PostPosted: Tue Nov 27, 2018 7:01 pm 
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blue is oil


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