Cylinder damage

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  1. #1
    Senior Member Array painlessauto's Avatar
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    Default Cylinder damage

    I am switching to twin turbo so I removed the engine for the cam swap. Checking things over I noticed cylinder #4 was an oil burner. The engine has 1800 miles on it, mostly cruising, wot blast (25# boost) here and there. I removed my head's today figuring I would have the guides checked and was surprised to see the cylinder walls in such poor condition. Can someone shed some light on what's going on here? I'm assuming slightly too tight ptw.

    Ptw was set to .0045"
    Iron block bored +.020"
    File fit total seal AP rings
    (.025" top ring.028" second ring)
    Coolant temps would peak around 190* during summer.

    My pistons don't look bad. Skirt coating is worn off a few but nothing crazy. No scoring on the skirts. I'm going to clean them up and check the ring lands along with everything else.


    Thanks,
    Matt

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  3. #2

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    Matt, I. thought I had replied to this post but apparently got interrupted and forgot to send my commentary, Here is an abbreviated version of it;

    The honing marks in the cylinders look good, the scuffing on the walls is ring related. Total Seal put me onto a product of theirs a few years ago called Quick Seat. I think it is a dry lubricant but I am not sure. I am sure it seats rings like nothing else I have ever used. If you use it those scuff marks will never appear again.

    A 0.020" overbore is too much for an aluminum block and (for my preferences) maybe a bit much for an iron block. I like to stop at 0.010" oversize maximum ad usually sell the aluminum blocks after 0.007" oversize. The issue is both remaining cylinder wall thickness and for supercharged engines getting adequate radial tension on the rings. N/A engines can use ring sizes the same as the bore size. Blown motors should always use a 0.005" oversize ring for proper blown motor radial ring tensions. That means 0.005" oversize up through about 0.003 to 0.004" oversize. I generally go to a 0.010: ring for bore sizes of 0.004" larger cup to 0.007 " larger. After the 0.007" o/s build I sell or sleeve the block to bring it back to standard — I am after the ring tension. At 0.008" there is no 0.015" oversize ring package so the block (for me) has outlived its usefulness at that point.

    The 0.045" PTW for a race only engine is probably OK. My personal preference is 0.003" or smaller of you have the right cam shape on the piston skirts. There is a company called Line-2-Line. They manufacture abradable coatings. that are used in a variety of industries. At one point Whipple used them for their rotors. The upshot of the coatings is they wear down to the optimum shape for the coated object. In the case of pistons that is the optimum cam shape for the skirt. At that point they stop wearing.

    The process costs about $300 or $330 (don't remember which anymore but it really works. Put its on the skitrts of your pistons, go with the close fit option they have and the pistons will go in with 0.002" or maybe a little less PTW. After you run the engine for a day or so the skirt coating will abrade away until the skirt makes fun contact with the cylinder wall. At that point it will stop and you will have the optimum PTW clearance and also the optimum skirt cam in the piston for your engine.

    You can refresh this at each rebuild as often as you want until the piston collapses so badly you wouldn't want to use it anymore. The fit, performance and silence of the short block assembly is nothing short of stunning. Ring life is extended because the piston rock is minimized and all manner of good karma comes to rest on your engine build.

    Here is their website => Line-2-Line Coatings



    Ed


    p.s. Between the Quick Seat and the Line-2-Line stuff you'll Never see those scuff marks again. Almost forgot don't forget to replace the rings and check the ring lands in the pistons to make sure they are still serviceable.
    Last edited by eschaider; 11-27-2020 at 08:20 PM. Reason: Added Postscript

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    Senior Member Array painlessauto's Avatar
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    Ed,

    I did use total seal quickseat when building the engine. I agree with you, it is excellent stuff. This is my second engine I've had to rebuild due to cylinder wall issues. As you can imagine I want it perfect this time around. 3rd times the charm, right?

    In regards to the ptw clearances... I was thinking of setting the clearance to whatever gibtec suggests. Odering the piston skirts bare and having line2line coat the skirts to tighten them up. I drive by them daily, they are 5 minutes from my house which is a plus.

    My brother has a set of Gibtec pistons in his 5.4 4v build with an iron block. They suggested .005" ptw which he did. I assume they will most likely suggest the same for my pistons.

    Should I tighten up the ptw to aeound .003" and use line2line or should I set it looser and use line2line?

    Thanks,
    Matt

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  6. #4

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    Line-2-Line has two different coating thicknesses they can offer. Us e the one that gives the tightest initial PTW and it will wear in to the optimal PTW setting for you by just driving the car. My bet is Gibtec will spec the PTW for a 4.6 at either 4 or 4.5 thousandths. The Line-2-Line coating will reduce this to probably .003 or less and give you a very good experience. Gibtec has evolved the skirt cam on the pistons over the years and it is better than ever right now. That said the Line-2-Line approach will improve on the as machined condition.

    With respect to the cylinder wall scuffing, if your ring gaps were not at large as they are I would suggest the rings were butting but at 0.025 /0.028 they are definitely not butting. Even though you use the Quick Seat be sure to adequately oil the ring lands and the rings prior to assembly. Whit what you are doing and the techniques you are using I am quite surprised to se the cylinder scuffing you are experiencing. Although I would bet dollars to doughnuts that it is ring based scuffing, it doesn't hurt to inspect the rings to see if you find corresponding ring race scuffing the lines up with the cylinder scuffing.

    Somehow those cylinders protective oil film either broke down or never existed at the scuff points. Either way you want to avoid a repeat performance. Make sure the Quick Seat changes color when you put it in. If it doesn't, then you need to clean the cylinder and take a second swipe at it.



    Ed

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    Ed,

    The total seal quickseat left a green hue on the cylinder walls, they were clean. The gaps were definitely .025"/.028"

    One thing I did not do is oil the rings. That very well may be my issue. I appreciate the insight

    Matt

  8. #6

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    That green color is what you want to see, Matt. You absolutely need to oil the ring faces and the ring lands. The cylinder wall scuffing is from the dry ring face. A dry ring in a dry land will also erode the land and ruin the pistons, Be sure the lands and rings are lubed on the new pistons and you should be A-OK on this round.


    Ed

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    Took a look at my pistons today. Cylinders 2 & 4 had top ring land damage.

  10. #8

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    That is looking like a lean condition, heat related failure, Matt. Did you buy eight or ten pistons when you built it? If you didn't buy ten take a look at Gibtec's for the replacements. If you did buy ten pull out the spares to replace the dead soldiers. If you go to Gibtec's, for the rebuild, while they can make an identical piston to your originals at any time, even down to the gram, it is more cost effective to order the spares when you first place the order. One off runs later, become more expensive because a single piston has to support all the set up costs.


    Ed


    p.s. Don't forget that the size increments on Gibtec's are not 0.010" and 0.020". Gibtec will make the pistons in 0.001" increments. That will substantially extend your block's useful life.

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    I'll be running Gibtec pistons this time around. I just measured all the bores in my replacement block. The largest cylinder is 0.0016" over the standard 3.552" bore size.

    What size pistons should I run? I'm not sure how torque played affect cylinder sizes.

  12. #10

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    Hone the block the minimum to get clean straight bores, Matt. As soon as there are no more shadows on the liner from low spots you are done — stop! Before you begin find the largest hole and hone it until it just cleans up. What ever that bore is that will be the bore that determines your piston diameter. Size all other bores to the same diameter and then tell Nick what that bore size is and have him make pistons for that bore. Nick usually recommends a 0.004" to 0.0045" PTW clearance so if you have a tuning or cooling system problem and the engine overheats you have a little more wiggle room. If you maintain the engine at a 180˚/190˚F operating temperature you are more than safe at 0.0035 PTW. If you can consistently keep at or below 180˚F then 0.003" PTW will work nicely.

    Tell Nick you would like to run a tight PTW and a cool (170˚F) engine for a tighter PTW. I would talk to Nick about having Gibtec provide the pistons with the Line-2-Line (<= clickable) coatings or just send the pistons out after you get them. The Line-2-Line turn around is less than a week.

    The Line-2-Line coating is a special abradable coating that will wear to the optimal clearance and stop wearing! When you look at their site you will see twin screw rotors. They did the coatings for Whipple on the second or third generation rotors. After the rotor runs in the coating abrades away where it needs to and doesn't;t where it does not need to, providing the optimal shape / contour for the rotor. I suspect but do not know that these coatings were helpful in later design rotors Whipple brought out.

    What I do know is if you get their tight fit finish it goes in at 0.002" or a whisker less and wears in to the optimal skirt cam in a matter of a few days. When you take the engine apart you will see the most stunningly uniform skirt loading across the entire skirt face — really impressive! An extra added attraction is the fact with the reduced PTW clearance the rings seat and seal better because they are not being wiped about the wrist pin centerline as much because of the reduced PTW clearance. When Line-2-Line did my pistons I think it was around $300 and in my opinion well worth it.

    What the Line-2-Line guys do, for almost anything, borders on magic! You will like them.


    Ed

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