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Classic Mustangs Tech Forum

Technical discussions specific to 1964-1967, 1968-1970, and 1971-1973 Classic Mustang. Discuss all tech related to in-line six cylinder and V8 powered Vintage Mustangs here.

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Unread 01-31-2011   #1 (permalink)
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Default 1965 V8- scratches in cylinder wall- hurting anything?

Ok, so I recently replaced most of the gaskets on my 65 V8 after finding a blown head gasket. While the top end was apart for the first time in what i would assume to be years, i took the opportunity to give everything a good cleaning. Considering the rest of the car is falling apart thanks to rust, I was pleasantly surprised to find so much shiny metal in the block. The few cylinders whose pistons were at less than TDC had relatively smooth, good looking walls...all save for one. The number two cylinder looked like someone just took a knife and scored vertical lines all around the bore. I read in another forum that vertical scratches like this can cause oil leakage/burning, which would explain why I often smell oil whenever I punch it. I think this cylinder has been like this for a while, and that the bad head gasket had nothing to do with it...it just helped bring it to light. Taking into consideration that this is a daily driver, and that's all she'll ever be (no racing!:nogrinner), is this a serious problem? Or should I consider having the block honed/bored to correct this? I've attached a picture of the offending cylinder so you can see what I'm talking about...
Any insight and thoughts are welcomed
Thanks in advance guys!
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Unread 01-31-2011   #2 (permalink)
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I'm gonna bet that that cylinder has drawn moisture at some time while sitting and rusted the rings/cylinder wall hence scoring the wall once it was re-fired. It really does not look to good to me, but if it is running now and only burning a little oil - I'd have to say it's fine until the oil comsumption gets to bothering you or the compression drops off and power loss follows. Typically the power loss won't show up until several of the cylinders wear out for a typical stock motor.

If it were me, I'd rebuild it, but there are alot of motors out there that go for years with worse problems. The cheapest thing you could do would be to get a set of rings for that one piston (if you can even buy just one set for one piston) and have the cylinder honed. I would talk myself into rebuilding it if I were to go through the effort to pull the motor, break it down, hone it replace the gaskets, put it back together, & put it back in the car. Of course one thing leads to another and I've talked myself into new heads, intake, carb, headers, etc, etc AND a year/two later...

It may even take boring to clean it up. Run it till it drops OR rebuild it. I don't think it will be catastrophic failure so long as your not abusing it.
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Unread 01-31-2011   #3 (permalink)
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She's been running progressively better since I bought her two years ago. I've put alot of work into the car and am really happy with how its turned out. I just got a vacuum gauge and compression tester just to get an overall idea of how healthy the engine is. Too cold to spend time doing the compression test right now, but the vacuum readings were actually pretty good (much to my surprise!). I haven't really noticed any power loss, nor excessive oil consumption. Like I said, only thing I've really noticed is the smell of burned oil whenever I really gun it, which isnt often. I wouldnt say I abuse it, unless you count the occasional sprint down the back country roads as abuse tehe . For now, I think I'll stick to my original plan of driving it till it falls apart. At this time rebuilding isn't really an option on minimum wage while at college haha
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Unread 01-31-2011   #4 (permalink)
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I would think the rings in that cylinder are badly broken and/or stuck and not contacting the cylinder walls at all. What is the measured compression for that cylinder compared to the others?

Scratches like that would keep the rings from sealing against the cylinder wall but from what I see there aren't any rings rubbing on that wall anyway.

You may be running only on 7 cylinders.

Oops. I agree, your weather forecast does NOT look good for a compression test for a few days unless you have a warm garage.
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Unread 01-31-2011   #5 (permalink)
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hello, Run it maybe put some marvel mystery oil in with the next oil cahnge that should be now after a head gasket job. Try some top cylinder lube ( you mix it with the gas) these may free up any stuck lifters rings and valves. next oil change do the compression test the weather will be better by then.

Ken
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Unread 01-31-2011   #6 (permalink)
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@Ivy66gt- Havnt done the compression test yet, but once I do i'll be back on here if I find anything unusual. I'll probably do a leak down test while I have the plugs out for the compression test; that would be an even better indicator of ring damage/severity of cylinder wall damage, would it not? If compression is lower on that cylinder, that might explain the awkward stumble she has at idle...not really rough idle, more like one cylinder is a tad off, making the idle sound slightly uneven. I hope I'm running on all 8; after all she sure sounds like she is haha. If the compression is off, but not by much, I think I'll just keep driving her for a while. I recently stiffed up the frame with some subframe connectors I made up, and she's been a blast to drive.

@kb65- I actually have been using top cylinder lube from Lucas for a while, originally i thought the rough idle was from something in the carburetor or top end; doesnt seem to have made too much of a difference in the idle but it has to have cleaned things out, cos she doesnt smell like burned and fouled gas at start-up anymore . The head job was about a month ago, but I'll def. try the mystery oil on the next change. One thing I've noticed is that the oil seems to be getting dirtier faster recently..may just be me tho haha
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Unread 01-31-2011   #7 (permalink)
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Quote:
Originally Posted by sparten512 View Post
I'll probably do a leak down test while I have the plugs out for the compression test; that would be an even better indicator of ring damage/severity of cylinder wall damage, would it not?
Yes, definitely. Compression tests can sometimes look pretty decent even with fairly bad leakage. Leakdown is much more informative but not everyone has the equipment. Actually only takes an air compressor, compression tester hose hookup, stop watch and a calculator but that's another, sort of long story with a lots of math. A leakdown tester is a lot easier.
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Unread 01-31-2011   #8 (permalink)
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Well, seeing as I have a compressor, air regulator and gauge, and the compression tester hookup, would it be too much to ask for the long story? Calculators and math arnt really too big a hurdle...my actual "profession" is an electronics engineer, I design guitar amps as a hobby
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Unread 01-31-2011   #9 (permalink)
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Do a wet/dry compression and compare the readings.
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Unread 02-01-2011   #10 (permalink)
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If you want to keep the car for a long time and stock i would rebuild it fully.
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Unread 02-01-2011   #11 (permalink)
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OK Dan, you asked for it. Here is a Purdue/Stanford EE's method for a leakdown test.

A standard leakdown test measures the cylinder air leakage at 100 psi by measuring the differential pressure drop across a small orifice as the leaking air passes through. This method measures leakage directly using PV=nRT which you learned in Physics class.

Calculate the amount of air in your compressor tank using PV=nRT at the known pressure when the tank is 'full'. I was using my small compressor which has a 7.5 gallon tank at 103 psi. Adjust for atmospheric pressure if you are not at sea level: I live over 6000' AMSL so I calculated using 12.25 psi as 1 atmosphere, NOT 14.696. That gave me 115.25 psia in my tank or 222.56 liters of air if it were at STP. You can get really precise and add in the amount of air in the hoses, etc., but that is not usually very much. My 50' hose only holds another 0.15 liters of air - not worth considering.

For each cylinder, time the discharge of air into the cylinder (with the compressor unplugged so it won't cycle back on) and record time and tank pressure. For each pressure you can calculate STP liters of air in the tank so you will know how much air has discharged through the cylinder vs time. You will essentially be measuring the time derivative of the amount of air in the tank in liters/sec.

Different brands of leakage testers use different sized orifices so the percentage numbers they give are different for the same engine. Since they use 100 psi in, they all call the pressure drop in psi across their orifice as the 'percent leakage'; i.e. a 5 psi drop is 5%, more leakage producing a 10 psi drop would be 10% leakage. The best I can determine a 20 liter/sec leakage rate will be read as anywhere from a 2.9 to 11% leakage from various commercial leakdown testers which gives you an idea of what is good vs. bad. Less leakage is always better but anything in the 10-20 liters/sec is not all that bad.

My various engines that I have measured take anywhere from 39 seconds to 3+ minutes to discharge my 7.5 gallon tank from 103 to 70 psi. 39 seconds is God awful with all broken rings. 3+ minutes is nigh onto excellent. I actually calculated the exponential pressure drop in the tank vs time and leak rate so all I had to do was measure the time from 103 to 70 psi (when my compressor goes 'click' to start up again) and not have to measure any other pressures or times. Both pressures are determined by the hardware; all I have to do is measure stopwatch time between those two points and not even look at the pressure gauge. The Excel sheet then tells me what kind of a leak rate was required to discharge the tank in that amount of time. For really leaky cylinders there isn't any time to measure much else except the 103 to 70 times.

A big huge Excel sheet is useful to do all the calculations of how much air is in the tank vs pressure, etc. It sounds complicated but not really. Once you have done it a few times you realize that the time to leak from 103 to 70 is as good a metric as any other and you will end up comparing your known good engine times to the one you are testing. If it goes to 70psi in 10 seconds you should, or may already be walking. If it takes 5 minutes your engine is just fine, etc. The Excel sheet will give you the liters/sec leak rate if you need to know more accurately what you have measured.
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Unread 02-01-2011   #12 (permalink)
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Uh, Wow, thanks! Wasn't quite expecting such an in depth explanation, but that wasn't too hard to follow. Its nice to still get the chance to converse on higher level once in a while .
So, I guess my over-all question is: If the compression test shows good, and the leak-down test shows ok and only moderately leaky on the bad cylinder, is it going to cause any irreparable damage to the engine if I keep driving? After all, I'm guessing its been in this condition for a while, and I've put almost 6,000 miles on it since I bought the car. If its more just a hassle than a threat, I'll just do my best to keep her chugging till I can afford to rebuild it. She's just my daily driver, and I have no intention of making her 10mile a year show piece or a high performance torque monster. I understand owning a classic car comes with certain "extras", all of which I am happy to deal with. When I bought the car, half the carb was missing, power steering ram punched a hole in the frame rail, the springs were propped up, the alternator was putting out 9volts and nothing electrical worked. Compared to what I started with, I'd be happy to put up with a little excessive oil consumption and a lumpy idle.
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Unread 02-01-2011   #13 (permalink)
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If the scratches are due to broken rings then there is always the chance that they can dig deeper and deeper making the cylinder worse. There is a limit as to how much you can bore the cylinders (0.040 according to Ford). If its really got broken rings your leakdown test will not give you good numbers.
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Unread 02-01-2011   #14 (permalink)
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Yeah, that makes sense..ok, well I'll wait out this ice storm we've got coming then do the leak down test and go from there. If it turns out the rings are more or less gone, is a ring job something i could feasibly pull off in my garage? Every repair save for some frame work has been done by yours truly...my first summer with her was spent on my back on a creeper, my laptop at my side with the forums and the ford manual up. I am not against doing the work myself, seeing as it'll probably save me a boatload of money in labor. A heads up on difficulty level would be nice tho .

In the meantime, more Lucas Upper cylinder cleaner & TLC will keep the old pony goin'.
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Unread 02-01-2011   #15 (permalink)
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*sigh* darn slow internet...double-post, sorry

Last edited by sparten512; 02-01-2011 at 06:47 PM. Reason: double-post
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