Fresh heads on high mileage engine
09-01-2005, 11:34 PM
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Fresh heads on high mileage engine Hey guys I doing a cam swap(cheaTR) and I took my heads to the machine shop to have the spring install height set up and they talked me into getting a competition valve job done. Now I'm starting to think about something I've heard for a long time, which is that if you put new heads or get a fresh valve job done and put the heads on a high mileage engine(mine has 112K)you will blow the rings out due to the now increased compression on the old rings. It sounds logical but I've only heard this I've never actually seen it happen. Just wanted to see what you guys thought.
09-02-2005, 05:25 AM
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I had the head on my '90 model Mitsubishi fully rebuilt (all seals, gaskets and valve job) at @200,000 miles. I did not touch the bottom end other than to clean the carbon off the pistons. The car now has 252,750k on it and I have had NO issues at all. My car does not smoke or leak any more oil. It does drink about a 1/2 quart between changes but I attribute that to the rings having 250,000+k on them...
I think your car will be fine with the fresh heads that you put on it. If your bottom end was not having problems before than you should not have any problems now IMHO.
I think your car will be fine with the fresh heads that you put on it. If your bottom end was not having problems before than you should not have any problems now IMHO.
09-02-2005, 12:20 PM
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Originally Posted by frodo84
I would do a leakdown test before I took the existing heads off..that should tell you if you are okay. Just my opinion, of course.....
09-02-2005, 12:58 PM
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A valve job does not increase compression ratio. It will just pick up some flow on the heads. Even if they mill them a little the compression wouldn't change much. Putting a different cam in has the biggest effect on the motor. The LT1 motors are the ones that die if you mess with them with milage. I think you will be ok. I would just start to save for a refresh on the block if it has 100+k miles already.
