engine overhaul: how clean is clean?

Discussion in 'Diesel Engines' started by CDK, Mar 9, 2012.

  1. CDK
    Joined: Aug 2007
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    CDK retired engineer

    Because I found nobody within reasonable distance, I decided to undertake the job myself and dissected one of my boat engines.
    Theoretical knowledge I do have, but practical experience next to nothing.

    One of the issues is the mating surface between the alloy head and cast iron block.
    If I were to write an overhaul manual, I would put emphasis on cleanliness, avoiding scratches and not to use sanding paper. Yet the surfaces should be immaculate before the new gasket is installed. But when I pulled the head, half of the gasket remained on either surface. I really had to peel that off, but there still is a lot of hard black lacquer-like stuff clinging to both surfaces.
    The cast block will tolerate some scraping and sanding, but on the soft head whatever I do leaves marks.

    Is there any proper way to do this ?
  2. michael pierzga
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    michael pierzga Senior Member

    Perhaps solvent will soften the compound. Heat may help.

    For delicate mating surfaces that I dont wish to damage I use a plastic scraper.... A piece of plexiglass sharpened to a razor edge with a bench sander. .
  3. Submarine Tom

    Submarine Tom Previous Member

    There is a lot to be said for scraping with a burred edge scraper. It doesn't take much of a burr and can be very tidy. Of course there's always fine sand paper, I prefer wetted, wet/dry.

  4. cor
    Joined: May 2008
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    cor Senior Member

    Auto parts stores here sell spray cans of "gasket remover" that work wonders on those old stuck on gaskets. If you can't find that, try a van of oven cleaner.

  5. WestVanHan
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    WestVanHan Not a Senior Member

    A single edged razor blade-carefully used preferably with a holder- along with soaking in solvent will do.
  6. jehardiman
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    jehardiman Senior Member

    Sounds like someone used a gasket sealent on the head gasket, generally a no-no. solvent and then wire brush to remove most of it.

    Is the new head gasket a composite one? If it is, don't worry about wire brush scratches, they are less than the machine finish roughness expected. You only need perfect surfaces for metal gaskets or steam casings. Blue...scrape...blue...scrape...blue...scrape....
  7. powerabout
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    powerabout Senior Member

    draw file with wet and dry over your file
  8. mydauphin
    Joined: Apr 2007
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    mydauphin Senior Member

    You can always do like 120 grit sandpaper to get stuff out and follow with something like 400. Just do it gently were you need to do and don't sweat, people have done it for years.
  9. Petros
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    Petros Senior Member

    I have done lots of engines, including high performance racing engines. The head gasket surface is one of the most important of the whole engine, it holds the most pressure and must be done properly, all of the old junk must come off.

    If the stuff is really stuck I use a wood chisel with a fine edge, just be very careful not to gouge the surface. I also have a precision steal block with square edges that also works well to slide across the surface to remove most of the old gasket. Small scratches are not a problem, they will clean up in the next step.

    Once the heavy stuff is off you can use a surface plate with 400 grit wet and dry. I like using a piece of granite counter top, you can usually get a scrap for free from a place that makes and installs counter tops. A steel plate with a very flat surface will also work. Use spray adhesive and stick the paper on the slab. Use solvent on the surface and either slide the head back and forth across it by hand, using even pressure, or using it like a large sanding block on a blocked up and level head.

    Keep doing this until all of the old stains and gasket marks are gone, you may have to change the paper several times. Wipe off and clean the surface and sand paper several times, and apply fresh solvent.

    With care you can make a better surface than a machine shop this way. You should also do this on the top surface of the block as well, it will make it very flat. Check that the head is flat with metal straight edge and feeler gauge, should be less than .002" out-of-flat when you are done.

    When you instal the gasket the surfaces should be very clean and the new gasket installed dry. Use solvent and white paper towels on the surfaces, keep wiping until they come off the head and block surface clean. Avoid handling the gasket, the silver color of it is graphite to allow relative movement between the two surfaces since cast iron and aluminum expand at different rates. the more uniform and smooth the surface the longer the bond will hold.

    make sure you also clean the bolts and the bolt holes real good with solvent and a stiff brush (there are small bottle brushes that you can use in the bolt holes). Use some kind of thread lubricant on the head bolt threads like high temp grease or antiseize compound, and under the head of the bolt too (auto parts stores should sell thread lube). And follow the torque tightening sequence in the service manual in several passes, up the torque reached each time until you get to head bolt torque spec. This will prevent damaging the head gasket and create a uniform clamp-up of the head.

    This is how we built up 1000 hp racing engines, and never had one fail.

    The other surfaces that need to be very clean are the cylinder bores, especially after they are honed. Use the same procedure for cleaning the bores, soap and water and than solvent and white paper towels until they come out completely clean. The other critical surfaces are the bearings and journals, and bearing cap bolts. You must use lots of clean motor oil in the bore and bearings of course so you do not damage them on first start up.

    It is best to do this work up off the floor so you do not pick up dust and dirt from the floor. If you do not have an engine stand, a bench and blocks also works.

    doing your own engine repair can be very rewarding and/or very frustrating. So take it carefully and read up on every detail first from your service manual, or from good engine overhaul sites on the internet.

    Good luck.
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  10. gonzo
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    gonzo Senior Member

    Get a can of gasket remover. It softens the old gaskets.
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  11. PAR
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    PAR Yacht Designer/Builder

    I too have rebuilt or built new engines from the ground up. The head's "deck" doesn't have to be especially smooth, unless high output, but it does have to be flat. A new head will often still show the milling marks on it's face, where it was "trued" and the gasket material will easily fill this small imperfections.

    I use a thing commonly called a "wizzer wheel", which is a small disk of Scotch Brite pad like materiel, on a shank. This is chucked in a variable speed angle grinder or other moderate speed tool and it quickly removes stubborn gaskets, without deforming the aluminum head.

    Then again is ubiquitous gasket scraper, which is better then a straight edge razor, though not as sharp. If you use one of these take a fine file to the corners, so you don't dig in.

    Buy a Chiltons or similar repair manual and read up on the standard repair routines. It'll cover all the stuff we take for granted, like how to install a Heli-coil, remove stubborn bolts, torque sequences, etc.
  12. Frosty

    Frosty Previous Member

    You scrape it off then final clean with deisel and 120,. Scratches do not harm anything. As a RR apprentice in the 70's I have done so many of these.

    1000hp will be using copper gaskets or copper fire rings --different than a little VW deisel.

    I was also tought to dress with a file.
  13. CDK
    Joined: Aug 2007
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    CDK retired engineer

    Thank you all for your advice, especially Petros who wrote a concise instruction sheet.

    Using 400 grit on a flat surface would have been my preferred way to clean the head, but the camshaft is still in place and there are always 2 or more valve heads well above the surface. You could argue that an overhaul job isn't complete without dismantling the valve train, but there are various reasons to leave these parts in place, like the need for special tools I do not have access to.
    I checked the bearing clearances with Plastigauge and used some gasoline to check for leaking valves.

    The reasons for the whole procedure are poor starting, low power output and loss of oil pressure when warm. Starting and output issues were caused by defective glow plugs and an enormous injection timing error; the previous owner apparently replaced the timing belt without following procedures. Oil pressure loss was caused by a badly worn sleeve bearing of the intermediate shaft and an unhealthy oil pump.
    These issues I can all correct, albeit with some effort like making dedicated tools to replace the bearings and investing in a $200 dial gauge and adapter I will probably never need again.

    Of course I started by buying the Brooklands Workshop manual for VW diesel vans, which I found to be totally unreliable because it discusses 3 different engines in each section while ignoring specific differences.
    The fact that these are tiny engines compared to Frosty's 1000 HP doesn't make the job easier. VW mass produces small diesels and gas engines that all look alike at first glance but have very few interchangeable parts. Some constructions even depend on the year the engine was built. Lots of special tools are needed for removal and installing, simply because the production volume is large enough to justify them. There even is not a single pulley on the engine a standard puller can be used for.

    I tried oven cleaner, gasoline, diesel and acetone as solvents, used Michael's plexiglass scraper, but finally reverted to a utility knife followed by 400 gr. wet and dry.
    The head surface still doesn't look clean, but maybe clean enough.
  14. CDK
    Joined: Aug 2007
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    CDK retired engineer

    "Engines like that are often rebuilt in place. It's a real pain in the butt, though doable with careful prep and control. Controls would be isolation barriers (usually plastic sheeting) and working with a well cleaned (previously) compartment. "

    PAR, your message doesn't show in the forum screen, just as an email(?)

    I passed that station already. No place to stand next to the engines, arthritis steadily progressing.
    So I disconnected everything, removed the U-joint, unscrewed the engine mounts and ordered a mobile crane. While waiting for the crane with the boat open and the aft deck panels removed, someone noticed my toolbox and took it.... The crisis I guess.

    The engine stands on a small trailer, surrounded by removed parts and jars with bolts and nuts. I made some pictures before a started dismantling, but I need a miracle to get everything back together again.

  15. Boat Design Net Moderator
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