SuprSlow50 Posted February 24, 2011 Report Share Posted February 24, 2011 Ok, so I bought a Banshee a month or two ago, with the mods listed in my sig. I was told that it was a 421 Cub built by Dan Hull @ A&S, with a full drag port, and it was originally setup for alcohol with 39mm pwks. The guy I bought it from swapped the 39mm alky carbs out with 35mm pwk gas carbs from his buddies 421 cub (supposively built at same time by Dan Hull) before I came and picked it up. It was suppose to have 165psi (which seems low for an alky motor to me, but correct me if I am wrong). I pulled the vf3's out and there is still casting inside the intake so I am guessing this is not a drag ported cub, I did verify the pistons are 573m06800, and the stroke is 58mm. Just did the compression test and came up with 140-135psi, for the left and right cylinders respectively, and the squish was right at .0425" and I tried to measure the base gasket and came up with .018" and it doesnt look like there is any gasket inbetween the head and cylinder, but looks like Yamabond. What should I do, replace the rings and get an aftermarket head? One thing I haven't done that I really should do is a leakdown test, and I am sure I will hear that from all of you. But other than that, what would you guys reccommend?? Quote Link to comment Share on other sites More sharing options...
dirtydownunder Posted February 24, 2011 Report Share Posted February 24, 2011 most power from porting is done on the exhaust and transfers, but you would think they would at least clean up the cast flaws in the intake, but you never know, if you take your head off you'll see if it has or not. if your head had been re chambered, id just take it off when you do and cc the combustion chambers to see where you are at, or just find a cool head with some 21 or so cc domes, depending on what fuel you want to run. .042 is on the tight side for a 4mm, but i dont know how A/S build motors, have you tried calling them and asking about there stock head 421 motors ? ive never done a leak down before, up to you. while its together you can check, or you can just buy some seals, gaskets and rings and rebuild the sucker. if you put a lil bit of oil down the cylinders, does the compression come up ? ( oil will help seal the ring to the bore, if you get a substantial amount difference, your rings are worn. did you try another gauge ? Quote Link to comment Share on other sites More sharing options...
SuprSlow50 Posted February 24, 2011 Author Report Share Posted February 24, 2011 Thanks Dirty.. I wasn't sure how much they port the intake area, that's why I was asking you for pics of your serval setup, but I can tell that nothing has been untouched in the intake port, but I haven't had the cylinders off to check the transfers and exhaust. Is it normal to not see a head gasket and instead see Yamabond coming from inbetween the cylinders and the head? I thought that was odd, and thought you only used a gasket or o-rings with aftermarket heads. I have tried calling A&S when I first bought the Banshee but have not gotten ahold of anyone or received a phone call back, so I just stopped calling awhile ago. I guess I will def. have to throw some oil in the cylinders and do a wet compression test tonight to find out the condition of the rings. I used both a Snap-on compression testor and a generic Auto Zone tester and came up with the same compression in each cylinder. I will post the results as soon as I get them. Quote Link to comment Share on other sites More sharing options...
sleeper06 Posted February 24, 2011 Report Share Posted February 24, 2011 IMO 42 squish is to tight for a cub,I like to be around .0050,if the motor was set up for asphault 165psi could have been the goal for the build.High compression isnt everything in racing.No head gasket is sketchy tho.I also have a drag ported 421 cub from fast racing the intakes and transfers are untouched and still have all casting marks the port heights have been altered but looks stock after fresh nik Quote Link to comment Share on other sites More sharing options...
gst_r Posted February 24, 2011 Report Share Posted February 24, 2011 Just as info my builder mod the stock head to use o-ring on it...so no gasket just o-rings around the chamber area... Quote Link to comment Share on other sites More sharing options...
SuprSlow50 Posted February 24, 2011 Author Report Share Posted February 24, 2011 Just as info my builder mod the stock head to use o-ring on it...so no gasket just o-rings around the chamber area... I was wondering if that was done to my stock head, but I have never heard of it being done before. And yes, this bike was originally built (again, from what I was told) to be an asphault drag bike on alky with 165psi compression. When I do a wet compression test tonight, if I find that the compression raises back to where it should be or close to it (165psi), would it be time to replace the rings seeing as it is down nearly 30psi? Quote Link to comment Share on other sites More sharing options...
SuprSlow50 Posted February 25, 2011 Author Report Share Posted February 25, 2011 Ok, so I just got done doing another compression test with a little oil in the cylinders and it went from 140psi and 135psi to 158psi and 149psi. Now then question is should I put new rings in it right away, or can I wait awhile? Also, is it ok to just re-ring it or should I replace the pistons too? I'm thinking that when I have the head off I should check the piston to wall clearance and use that as a determining factor as to whether or not I have to replace the pistons?? Thanks for all the help and info guys. Quote Link to comment Share on other sites More sharing options...
sleeper06 Posted February 25, 2011 Report Share Posted February 25, 2011 100% use the clearance as a dtermining factor,also make sure there straight n round if your bore isnt perfect your rings wont seal and will flutter Quote Link to comment Share on other sites More sharing options...
SuprSlow50 Posted February 25, 2011 Author Report Share Posted February 25, 2011 What should the clearance be? Do you think it is necessary to replace the rings and tear it down now? Quote Link to comment Share on other sites More sharing options...
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