sealing engine cases

[taber hodaka]

I use yamabond to seal my engine cases and I have a question for all you wizzards out there. What do you use to get the old sealer off when you split the cases besides a razor blade?-------------Clarence

[Bullfrog]

That is exactly why I don't use Yamabond (or any of the solvent-cement types of sealers) -- they are so dang hard to remove.

For years and years I simply used silicone sealant (yes I know it softens - but it can't go anywhere in the case seam after it softens and it still seals) partly because it can be rubbed off with your thumb when rebuild time comes around. More modern folks have convinced me that anaerobic sealants are the proper thing to use now. They apparently are designed to withstand petrochemicals . . . and still remove with a good thumb rub when the time comes.

Uh, . . . oh, . . . I'm sorry, but I don't know how to remove the Yamabond.

Ed

[BrianZ]

Lacquer thinner does a good job of removing Yamabond or Permatex Motoseal (same thing).

Years ago I used to work on old Triumphs and BSAs. I was told not to use silicone because if you happen to get too much on the cases (I know, just don't use too much), a piece can break off and plug an oil passage and ruin the engine. For this reason I started using Yamabond (or Motoseal), and have stuck with it ever since.

Brian

[hodakamax]

Clarence--This is kinda funny--As soon as your post arrived I was sitting within 20 feet of an Ace 100 with the cases split--I quickly grabbed a rag and some lacquer thinner and confirmed the answer is "lacquer thinner". Seriously, thats all I ever used (along with the blade) thru the years. I used an outboard motor sealer in the past and later to some Permatex product and now the Honda version of Yamabond. All seem to succumb to lacquer thinner. Whatever works is probably the answer--carb/brake cleaner is another option.

Maxie

[taber hodaka]

Thanks to you all, I hate to admit but some time early last year I rebuilt a combat Wombat engine. The cases were together and in a ziplock well I couldn't remember sealing the cases so guess what, it didn't come back apart very easy and it was sealed very well. I cleaned it up with a razor blade what a slow process. I keep a log on what I have done to an engine but I didn't mention sealing. I will probably go to what Ed is using. I had always used a light film of silicone in the past. Several locals that use yamabond are also having trouble removing it, I will share using laquer thinner with them. -----------------Clarence

[dcooke007]

I use carb cleaner and a razor blade held 90 degrees to the surface being scraped most of the time. Lacquer thinner works well also.

I have found a brush that has proved very useful for cleaning parts and removing sealer. If removing old sealer it works better with a cleaner / solvent. In the old days firearms were blued by a rusting process and still used in some high end guns today. The process forms a layer of very fine red rust on the parts surface and when the surface rust is removed with 0000 steel wool or a carding brush the surface rust is removed and the blued finish is uncovered. The brush has to be very fine of course or it would damage the new rust blued finish. This brush works very well for cleaning, removing rust and wont damage the aluminum. A light touch is required so you do not damage the brush. A full size wire brush and a tooth brush size is available. The tooth brush size would be correct for cleaning the sealant residue and the larger brush can be used for larger cleaning tasks that wont damage metal parts when used properly. I don't do rust bluing but always have these brushes on hand. Here is a link for the tooth brush size and you can search carding brush in Brownell's web sight for the full size brush. Come to think of it there is also a carding brush for your bench grinder. Currently they are out of stock. Just check back from time to time if interested.

http://www.brownells.com/gunsmith-tools ... d6732.aspx
Danny Cooke

[Dale]

Acetone on a Q-tip removes Yamabond easily. Just be careful using Acetone...

[Zyx]

All solvents require care in use. I have never used silicone to seal an engine case or a transmission case because it doesn't last. Right Stuff is an exception but I still would not use it to seal motorcycle cases. Yamabond or equivalent is made for that job, and I would rather use what is appropriate to the job than use something that is easy to remove.

As for the bluing process, bluing is an oxidizing process, but not a red rust process. You have to introduce particular acids to the process to get the blue color. In this case, selenious acid and phosphoric acid. The red rust process results in browning, not bluing. Most weapons up through the middle of the 1800's were browned, which process can be accelerated with uric acid (yes, just pee on it and leave it sit). Then remove the rust with fine steel wool, gently, then oil thoroughly. I have used both processes in making guns. Both are tedious to get right, bluing being the easier process to get right if you have a hot dip tank. Totally off topic I suppose, but we do take varied roads to get to old age.

[thrownchain]

Another thought here, when using any sealer on the cases, use very little, a skim coat is plenty, same if using it to tack on gaskets. I've had to dis-assemble motors where way to much was used and raised hell with oil passages. seized motors are no fun.

[Firehawkmph]

If I have the motor down to bare cases, I throw the cases in the glass beader and it cleans right up without hurting anything.

[hodakahagg]

My 2 cent's
permatex aviation form-a-gasket 3D item#80017 or 2B,2C also known as high tac by us old guys.a little goes a long way.cleans up with acetone.

[Zyx]

FWIW, lacquer thinner is acetone.

Yamabond 4, Hondabond 4, same stuff. Aviation Form-A-Gasket in liquid form, very close. K&W Copper Coat, very close. They all work roughly the same, but Yamabond and Hondabond are made for sealing two stroke engine cases. The reason it is hard to remove is the reason it works so well.

[junker2k]

I have used Gasgacinch for ever. The only gasket in any of my motors is the metal head gasket. It goes on easy, sets fast and cleans up very easy. I tried yamabond crap once and never again, it is just to hard to get off. Give Gasgacinch a try you will love it!
Jack K

[Zyx]

The cylinder base gasket is part of the deck height calculation. Removing it can lead to piston/head contact unless otherwise accounted for.

[junker2k]

The cylinder base gasket is part of the deck height calculation. Removing it can lead to piston/head contact unless otherwise accounted for.

Not much chance of the being a problem at 8.5 / 1 or even at 12/1 compression. When I worked at the motorcycle shop in Walla Walla way back when, we did hundreds of them this way. A big plus of doing it this way is that you don't match the gasket to the ports and it's very easy to clean up.
Jack K

[Zyx]

Depends entirely on the brand and built-in clearances of the engine you are referring to. Compression ratio is irrelevant in determining head clearance. It is simply a result of changing head clearance. Both my Hodaka engines will top out the piston within thousandths of an inch of metal to metal, even with a base gasket and even when staying within factory compression ranges. There is little room for error, at least with the ones I have.

Not to mention that dimensions change with temperature, and clearances change over the rpm band. Throw in a bit of debris, even carbon, and you can hit the piston on something it should not otherwise touch. There is a base gasket for a reason, and eliminating it raises compression, but does so without any science behind it. Raising compression raises demand for octane, increases loads on bearings and rings, raises internal temperatures, often requires changing ignition timing and spark plug heat range, and can, but most often does not, lead to holing a piston.

So, yes you can use sealant instead of a base gasket. You can even leave out the head gasket. But before you do, you might want to put it together as intended, with torqued head bolts, and verify piston clearance and head volume. I wasn't saying it can't be done, but I would say that what we used to do as younger folks is probably neither here nor there unless we were part of a racing team making closely calculated changes to engineering. Leaving out parts without calculating the changes is risky at the least. I was a mechanic for Honda and Yamaha in the 70's and service manager for a Honda dealer for two years during that time. I would NEVER have left out a base gasket on a customer machine if it came with one because of the potential for catastrophe.

Besides, with gasoline as it is these days, high compression is really hard to support. Real gasoline went out of production in this country 30 years ago. Better these days to err on the lower side of compression than overhaul a top end every other month.

[hodakamax]

Nice tech piece AZ. Not only that, removing the base gasket changes the piston port timing by that much. Closing the exhaust port early adds even more compression--It all adds up. Good job.

Max

[hodakamax]

Hey AZ--A little more on raising and lowering the cylinder. When brainstorming how to make a two-stroke go faster one thinks of raising port height--why not just raise the cylinder? Of course the piston will never reach the top causing loss of compression. Despite all this about the time 125 Hodakas came out a competitor we raced against thought this was the way to go. He manufactured and sold a base spacer that looked to be about 1/8 inch thick. He recommended milling the head and reshaping the squish area. Of course it didn't work--to get enough compression the head would probably have extend into the cylinder! Interesting you must admit but not practical. Further proof of concept was it was even easier to beat his 125 on our 100s. Thought you might enjoy this story from the past.

Sitting here watching it snow--

Max

[Zyx]

I would agree, even without testing, that merely spacing the cylinder at the base would have no net positive effect. Far more is involved in changing power by altering port height than merely raising the port. By spacing the cylinder, all ports are raised both at their top and their bottom. Plus the loss of compression, which is hard to recoup. Often, I would widen ports without substantially raising them, or raise only certain ports, but not all, or raise one more than another. Can't do any of that by spacing the cylinder at the base.

A lot of time and theory goes into proper port design. I don't pretend to understand all the ins and outs. Most often I would follow someone else's lead, such as the tech tips from Harry Taylor. About the only hop up I designed from scratch was an expansion pipe back when my Hodaka was a 100cc. It worked, but at a price. I was aiming at raising the output and the point in the rpm range where power was made. Did that alright. Made it so pipey that I couldn't ride in the woods due to loss of low end.

Small changes to intake, transfer, and exhaust timing can have large and sometimes unexpected results. Since it is hard to put back metal cut from a cylinder, I approached porting with caution and followed Hodaka tech tips as closely as I could. There is a lot if power lurking inside a Hodaka, but at the end of the day, they are all small displacement bikes. You can't make radical hp without sacrificing something else to get it. Usually torque and/or longevity.

I found that simply blue printing the cylinder was best if you were looking for all you could get without butchering the power band. That, and stuffing the lower end were things that worked, cost little, and did not hurt the life span of the engine. Rather than try to turn a modest 100cc bike into a fire breathing 125 MX machine, it is simpler to go buy one. But maybe not as much fun depending on your age and financial position. A lot of what I did, I did because I could not afford to go buy a bigger bike. So I worked with what I had, same as most others hereabouts.