Garbage Gaskets: Crank Case Too Tight

Discussion in 'General Questions' started by SEGACDX, Sep 4, 2016.


    SEGACDX Member

    I hate how finicky the quality of the gaskets are so I always opt for gasket makers because they work better and are cheap. I often have to rebuild,replace bearings or just fix leaks but sometimes it's just not easy.

    My last engine was a great FM80 I got from gas bike years ago worked a charm until the bottom needle broke after almost 5 years of use. Now I have a newer style engine with a much bigger crank compared to the old one.

    I have one problem, the crankcase is to small and crank is to big to turn freely without a stock gasket.
    It will still be tight with it, but with only RTV it's super tight and that's no good making a lot of heat very quickly causing loss of power and ware.

    I have used this for years on my old engine with great results for much longer over the crappy gaskets, it ran cool and had lots of power on all power bands.

    I am wondering if anyone else has run into this problem or knows there to buy a full copper gasket set because I am not getting theses shitty cheap gaskets anymore they last a few months and fall apart.

    Please don't tell me just use the stock replacements I do not want them!

  2. zippinaround

    zippinaround Active Member

    Look on ebay for heat and oil resistant gasket material ,i bought a sheet of it for about 5€ and have made gaskets for 4 engines already its pretty good, has kevlar in it i'll try to find link if your interested.

    SEGACDX Member

    I am very interested, I would be good to make my own gaskets, how do you make yours? as in how do you cut them.
  4. crassius

    crassius Well-Known Member

    there is often extra room, but crank cheeks sometimes rub on bearing housing just because bearing isn't all the way into housing on both sides - look for rub marks and try a thin shim between bearing and crank to move crank cheek away from housing on that side (sometimes where journal is swedged in there is a bit of metal sticking out that can be hammered down flat too
  5. Steve Best

    Steve Best Well-Known Member

    I had the opposite problem. Crank flopped back and forth with 1mm play. I shimmed the crank bearing. Pretty hard to cut crankcase gaskets, quite intricate. Well worth the small cost they charge.
  6. zippinaround

    zippinaround Active Member

    well first i trace it out then drill biggest hole first ,then smaller ones then cut the outline with a scissors some holes are small enough i use a hole punch but the one i have doesnt go very big, the old link i bought mine from is dead will search around a bit and see i know it was from a company in greece so they probably went bankrupt hahaha that is the company i got it from but they are no longer on ebay
    Thats the stuff i got gambit af oil
    Last edited: Sep 5, 2016
  7. butre

    butre Well-Known Member

    I've never seen a stock motor that didn't have at least 1mm of slop. I had one motor with about a quarter inch of slop a while back, no idea how they could possibly have that much variation.
  8. Steve Best

    Steve Best Well-Known Member

    You are making me feel better. I have 3 engines, Grubee 48cc, 66cc and a black 66cc. The unknown 66cc is the loose crank. It also has the tall piston. The Grubees have only a few tenths mm play.
  9. jaguar

    jaguar Well-Known Member

    I would put oil on the case, press it onto the gasket paper, and pull it off leaving the oil on it where you need to cut. Once the outer part is cut then place it onto the crankcase and use an exacto knife to cut out the holes. Then cut off the inner part.

    You can take the crank out and beat on the side of the crank wheel at the crank pin area to bring the wheels closer together (until there is minimum side play for the connecting rod) and then retrue the narrower crank.
  10. zippinaround

    zippinaround Active Member

    i've been thinking could we adapt a mini moto engine crank to fit in they are far smaller and can rev higher especially the balanced racing ones can reach 12000rpm!
  11. jaguar

    jaguar Well-Known Member

    It's easier to drill two holes in your crank wheels to balance the crank.

    SEGACDX Member

    I ended up testing the engine yesterday and my god what a waste of time it was to even fix anything, last time I did this I got a lot of heat so much my engine would be burning hot everywhere on the bottom end. This time I just get a hot and useless engine.

    I will have to get some gasket material and try these methods, thanks for the suggestions.
  13. Frankenstein

    Frankenstein Well-Known Member

    Yeah hot and useless, that's what big daddy likes to hear.

    Erm... Nevermind...

    I did think that idea with hammering the cranks together was a pretty good idea, where does one buy those shims anyhow, I have a few left over from motors that have been cracked open but I don't know where to get them.

    I also saw a motor with some very very bad play, like an 1/8th inch worth of slide between main bearings. It would actually push the thin crankcase seal out which is how the problem was discovered.

    Jag is it me or is it possible to take just about any engine kit and make it greater than great, or is there a specific motor one would buy to make mods to.

    For the most part it looks like they are almost all identical minus the variations for quality control.
    Last edited: Sep 7, 2016
  14. Steve Best

    Steve Best Well-Known Member

    For shims I used regular steel washers drilled to the specific size I needed. You want a close fit on the journal.
    I shimmed the wrist pin bearing as well. I needed a 16mm wide bearing and only had a 12mm, so put a 1.8mm washer on each side. Very important this bearing does not slip too far to the side. By taking a small diameter washer (M8 I think) and drilling it exactly 10mm I got the close fit, thickness and the small outer diameter I needed.

    Yes, I think you can do a lot to improve these motors during a rebuild, without a machine shop.
    This engine I am working on was a well worn generic and quite sluggish with a sloppy crank. Let's see:
    1) trued crank, it was not bad but is even closer now, done with a hammer, tested with a dial indicator.
    2) new seals and 6202 crank bearings (one journal was loose, punched and locktite to retain)
    3) stuffed the crankcase around the bearing retainers and lower transfer port trough
    4) oil flow holes to both crank bearings drilled
    5) matched the cylinder transfer port to the case
    6) new sealed 6202 bearings on the clutch shaft instead of the shielded grease leaking bearings
    7) case halves cylinder surface matched by file and sandpaper (on a smooth surface) before crank installed
    8) Lip taken off the inside edge of the transfer ports and small burrs removed, chamfered edges
    9) new studs and 8.8 grade Allen head bolts installed everywhere
    10) cut gaskets to fit intake and exhaust ports, trimmed case and base gaskets to fit
    11) drilled muffler flange (and gasket at same time actually) 3/4" to fit the exhaust port
    12) installed a crank seal retainer plate behind the stator coil (was missing)
    13) installed a thinner sprocket so lighter 410 chain can be used
    14) cleaned the burrs off the clutch shaft and push bar so it works freely and used waterproof grease
    15) Cut a 3mm squish band out to 47mm on the head at the angle to match the piston
    16) filed and sanded the head and cylinder flat (neither were) and set them up to a .8mm squish

    All of these are significant improvements on what is essentially a stock engine.
  15. Frankenstein

    Frankenstein Well-Known Member

    By the lower port trough you mean the part circled in this image right? draw1.jpg
    And how do you drill oil holes for what bearings?
  16. Steve Best

    Steve Best Well-Known Member

    Yes, those are the transfer port troughs. Here are the other details:

    SEGACDX Member

    Right now I am in the process of making my own gaskets on the cheap, I am using thick paper folder as cheap test gaskets before I order some Felpro.

    I took a measurement of the stock gaskets and they come out to 1/32" so I used 3 layers with one layer with adhesive to keep it all together. I hope for the best but will still be replacing it with good Gasket material, I guess I just wanted to see if I could and to get in some gasket making experience in there as well. If it works well I can use this method to make dirt cheap gaskets in a pinch.
  18. zippinaround

    zippinaround Active Member

    A friend of mine said he used flexoid gasket material its oil and water resistant but not high temperature said it worked fine and is very cheap 1$ a sheet or something and comes in various thicknesses.
  19. Steve Best

    Steve Best Well-Known Member

    Paper and cardboard work well for base and carb gaskets on 2 strokes.
    Temperatures are not that on the intake and case due to the cooling effect of the air/fuel mixture.
    The main thing you need is sufficient softness for surface defects and resistance to fuel and moderate heat.
    You can test the effectiveness of your gaskets (or sealant) by pressurizing the case (plug the intake and exhaust) to 5-7psi (use a bike pump only, or you will blow out your crank seals) and checking for leaks.


    SEGACDX Member

    I did end up making good gaskets with my paper folders but it is still not good enough for my whiny baby of an engine so I ordered some Fel-pro sheets in a set of 4 types for $11.74 on amazon. I will use the 3/64" or 1/32" or may even try out the thicker 1/16" and 1/8" for other things. I've looked into crank types and have found I am not the only one to notice the difference between the ZAE-50 and FM-80 cranks.

    I find it very annoying that the ZAE-50 Crank is not only bigger then the older FM-80 but the crank case is only slightly bigger but not enough to have good clearance.

    Even when using a 1/32" stock gasket it still rubs a bit causing heat, powerless and wear on the engine.

    All I expect is the newer engines made now to be as good as the FM-80 but I still cannot believe this is even a problem in the first place. You could install the crankcase with only RTV and it would hold up so well I would never need to worry about leaks for a long time.

    I could have just got a lemon but I have more then one crankcase with the same problems so this could just be a overlooked problem.

    Anyways I am going to try to cut some gaskets and get my worthless engine working properly.
    Here is the thread and an image from it that show how much bigger the ZAE-50 Left and FM-80 Right really are.

    Last edited: Sep 15, 2016