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post #1 of 21 (permalink) Old 12-26-2019 Thread Starter
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Case Gaskets?

I tore down my oldest motor for mock up reasons and was surprised to find a gasket in between the center cases. Not what I'm used to ... but I'm learning.

So do you guys replace these? Can you buy them somewhere? Make your own? How about doing without them altogether? Me and Yamabond are old friends.
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post #2 of 21 (permalink) Old 12-26-2019
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The gasket in between the case halves controls the end play you can buy gasket material in different thicknesses from the auto parts store and make them or you can buy them die cut from eBay

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post #3 of 21 (permalink) Old 12-26-2019
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Re: Case Gaskets?

Quote:
Originally Posted by pntrbl View Post
I tore down my oldest motor for mock up reasons and was surprised to find a gasket in between the center cases. Not what I'm used to ... but I'm learning.

So do you guys replace these? Can you buy them somewhere? Make your own? How about doing without them altogether? Me and Yamabond are old friends.
I mainly do the gasketless sealing method..

I also use MotoSeal...It's just as good if not better than Hondabond/Yamabond

Removing the gasket helps reduce some internal crankcase volume to enhance velocity..

If you take a whole gasket and cut out the crankcase area then ball it up that's how much internal crankcase volume is reduced..

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Last edited by CAM2; 12-26-2019 at 07:36 AM.
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post #4 of 21 (permalink) Old 12-26-2019 Thread Starter
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Re: Case Gaskets?

Thanx for what I'm sure will be an ongoing education. It seems the correct answer to my question is "all of the above!"

I'll do some endplay investigating first, but if there's room I'll leave the gaskets out.

I got more questions about about pumper carbs too. No experience other than 5 horse Briggs flatheads from back in the day and they seem to have come a long way since then.

With no float bowl do they need a petcock?

Does the return line need to enter the tank from above the fuel level? I've got pictures in my head of gas draining back the other way.

And Thanx again guys. I got a ton of experience on larger 2 strokes but that don't seem to be applicable here.

Last edited by pntrbl; 12-26-2019 at 12:09 PM.
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post #5 of 21 (permalink) Old 12-26-2019
Re: Case Gaskets?

Well, for one, you don't need a gas shutoff, but, all my pumper carb bikes have one. Why, if you pull the line to drain the tank, gas runs all over w/o one. Myself, like to leave about .015" end play on crank. .0075" each side. Use a feeler gauge to see how much you have then go from there.

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post #6 of 21 (permalink) Old 12-26-2019 Thread Starter
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Re: Case Gaskets?

Thanx EPR. I got a bung welded in the tank for a really cool old skool brass petcock. It's a keeper.

What I haven't got is a bung for the return line and I'm not sure where to put it.
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post #7 of 21 (permalink) Old 12-26-2019
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the return line can be anything even going into its own self 🙂
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post #8 of 21 (permalink) Old 12-26-2019 Thread Starter
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Re: Case Gaskets?

That raised my eyebrows! And it's good news too. I had a helluva time building the tank and I wasn't looking forward to messin' with that anymore.

Because of the fuel filter in the picture I'm assuming the lower hose is the incoming?
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post #9 of 21 (permalink) Old 12-26-2019 Thread Starter
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Re: Case Gaskets?

Just in case of painful lessons along the way I started checking crank clearance on my old motor. Cleaned the gasket surfaces 1st and then checked the depth to the bearing in both halves. They added up to 1.226, minus 1.188 for the crank, which leaves .038 clearance. Without a gasket? That seemed kinda big, so, not trusting my methodology, I repeated the process. Same thing.

Next, with nuttin' to lose, I screwed it together! The crank landed with .020 on one side and .018 on the other. .038. This pair of cases definitely don't need a gasket.

The only question now is am I gonna throw one half down on my little mill and start flycutting it. Would that be worthwhile?
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Re: Case Gaskets?

Quote:
Originally Posted by pntrbl View Post
Just in case of painful lessons along the way I started checking crank clearance on my old motor. Cleaned the gasket surfaces 1st and then checked the depth to the bearing in both halves. They added up to 1.226, minus 1.188 for the crank, which leaves .038 clearance. Without a gasket? That seemed kinda big, so, not trusting my methodology, I repeated the process. Same thing.

Next, with nuttin' to lose, I screwed it together! The crank landed with .020 on one side and .018 on the other. .038. This pair of cases definitely don't need a gasket.

The only question now is am I gonna throw one half down on my little mill and start flycutting it. Would that be worthwhile?
Tight tolerances and tool based engines don't mesh together too well besides these engines have a wicked thermal expansion rate....

Depending on whether you see the task of flycutting the case halves over shimming the bearings as being worthwhile in a volume reducing way I say just simply blueprinting what you have will work splendidly for your type of build...

Theres something to remember about modding these toolbased engines when running on pumpgas....Going too high on compression puts a lot of heat stress and pressure stress on the crank and crank bearings especially if you use a rocket key set advanced to enhance bottomend takeoff power..These factors are what makes a small single cylinder engine that's very sensitive when tuned to ambient outdoor temps meaning you'll be tweaking the carb a lot more than you'd desire especially if you start out on a journey starting from brisk morning temps and ending in moderately warm temps..…..

On my heavily modded stand-up scooters and cags I literally had a jewelers screwdriver stuck in the end hole of my throttle grips...…..LOL

You want to blueprint,polish port and balance your build with a squishband of .040" - .045" plus add 30-32 ounces of weight to your flywheel to enhance the juggernaut effect to give the bike an effortless feel with no engine lag when traversing uphill climbs with those larger sized bike rims...

For the muffler...….The faster you get rid of the gasses the better your engine will breathe and chug...…….

You don't need a extravagant exhaust pipe on a tool based engine.....It may look cool but will only add unnecessary weight plus rob time mounting it and limit spaces you cant get burnt unless you pipe wrap it...

A gutted box muffler with overly huge outlet will do more than well ...A similar method works great on chainsaw conversion engines....……

We didn't run no stinkin airfilters on them either...……….LOL



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post #11 of 21 (permalink) Old 12-26-2019 Thread Starter
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Re: Case Gaskets?

The painful and somewhat embarrassing lessons have begun. Everything I did made sense. 2 + 2 does equal 4. All was well and adding up like it's supposed to... until I went to give the crank a spin. The **** thing won't hardly move! And all I gotta do is loosen the screws and it's a loose goose.

Methinks it needs a gasket.

I dunno where all my precision instrumentation went wrong, but when the crankshaft's all bound up I know it went wrong somewhere.
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the most i whould do is blue and then lap the case halves on a glass table if you feal like it.

check the bearings that they are all the way seated in the case halves.

if you still have zero endplay you will need gaskets.

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Last edited by MrKitty; 12-26-2019 at 10:15 PM.
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Re: Case Gaskets?

Quote:
Originally Posted by pntrbl View Post
The painful and somewhat embarrassing lessons have begun. Everything I did made sense. 2 + 2 does equal 4. All was well and adding up like it's supposed to... until I went to give the crank a spin. The **** thing won't hardly move! And all I gotta do is loosen the screws and it's a loose goose.

Methinks it needs a gasket.

I dunno where all my precision instrumentation went wrong, but when the crankshaft's all bound up I know it went wrong somewhere.
Just pop out the bearings and set them a tad deeper using a Dremel or use thinner profile deep groove crankcase bearings....……..

The diminished crankcase volume is a golden thing to have in the world of building small cc two strokers...…

Another thing that comes to mind is the crankshaft itself...Afterall it is Chinese made…

An un-true crank wont sideload naturally and wont spin without binding...

Check the thing for trueness using VEE blocks and a dial indicator....

I guarantee youll see less than favorable runout results between the two halves causing the crankcase bearings to bind...

Theres even more binding with case seals installed too….

The fix is basically done by whacking the less-than-favorable un-true counterweight with a hammer to get it back to being true....LOL

I'd also tack weld the crank weights to the crankpin so it doesn't happen again...…….

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Last edited by CAM2; 12-27-2019 at 10:02 AM.
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Re: Case Gaskets?

Put a case gasket and put it back together, see what it does. DDM, Daves Discount Motors has .004" thick Zenoah 15mm ID crank shims. My question is, if you use a soft sealer, when you tighten the case bolts down how do you know when the case halves have to same space all around?? Only on a cyld base do I use Yamabond or what ever. I use crank shims if needed, and I spray all my gaskets with Permatex high temp copper head gasket spray, really sticky and gives good heat transfer. Everyone has there own way.

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post #15 of 21 (permalink) Old 12-27-2019 Thread Starter
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Re: Case Gaskets?

Figured out I was mis-reading my depth indicator yesterday. Instead of a satin finish it's a shiny thing and that makes it hard to see the lines in all that glare. I busted out with the magnifying glass today and got that straightened out. The case is 1.176 between the bearings so with a wider crank at 1.187 it's gonna bind.


I took a look at the crank too like CAM suggested and I think I may have tweaked the crank when I sucked the cases down over it. It was 1.187 at the pin and .007 shorter on the other side. Like it got squeezed? A wedge with a calibrated hammer fixed that and it was all good on the V-blocks. Under a thou.


With some .018 business card stuck in there to simulate a gasket it went together just fine. All's well. No bind. It just needs a gasket.


Still having trouble measuring the assembled clearance with a feeler gauge tho. It's like my hand gets in the way of the light and I can't see if I'm pokin' it in the right spot. I'll keep workin' on it.


Having all that under my belt I started looking at the 3rd port motor I'm planning on using. For some reason it has an extra 5 thou of clearance in one of the case halves. And a skinny crank! Together they worked out to having .002 of clearance and whaddaya know? That one bolted up without a gasket simulator and spins freely too



Something else I noticed is my fat crank has .009 of sideplay at the rod bearing. That's easy to measure with a feeler gauge. Meanwhile, Mr. Skinny has .019! These things are all over the map.


I'm gonna wait until I get some deep groove bearings pressed in to see where I'm at, but if I have to I could squeeze that skinny crank another 10 thou. It just means making stops that are .010 shorter and a push on the press. We'll see.



Obviously I'm gonna have to stumble thru this myself, but the benefit of all of the experience you guys bring to bear is a huge help. Thank You.
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Re: Case Gaskets?

Quote:
Originally Posted by pntrbl View Post
Figured out I was mis-reading my depth indicator yesterday. Instead of a satin finish it's a shiny thing and that makes it hard to see the lines in all that glare. I busted out with the magnifying glass today and got that straightened out. The case is 1.176 between the bearings so with a wider crank at 1.187 it's gonna bind.


I took a look at the crank too like CAM suggested and I think I may have tweaked the crank when I sucked the cases down over it. It was 1.187 at the pin and .007 shorter on the other side. Like it got squeezed? A wedge with a calibrated hammer fixed that and it was all good on the V-blocks. Under a thou.


With some .018 business card stuck in there to simulate a gasket it went together just fine. All's well. No bind. It just needs a gasket.


Still having trouble measuring the assembled clearance with a feeler gauge tho. It's like my hand gets in the way of the light and I can't see if I'm pokin' it in the right spot. I'll keep workin' on it.


Having all that under my belt I started looking at the 3rd port motor I'm planning on using. For some reason it has an extra 5 thou of clearance in one of the case halves. And a skinny crank! Together they worked out to having .002 of clearance and whaddaya know? That one bolted up without a gasket simulator and spins freely too



Something else I noticed is my fat crank has .009 of sideplay at the rod bearing. That's easy to measure with a feeler gauge. Meanwhile, Mr. Skinny has .019! These things are all over the map.


I'm gonna wait until I get some deep groove bearings pressed in to see where I'm at, but if I have to I could squeeze that skinny crank another 10 thou. It just means making stops that are .010 shorter and a push on the press. We'll see.



Obviously I'm gonna have to stumble thru this myself, but the benefit of all of the experience you guys bring to bear is a huge help. Thank You.
Don't forget that the bearing pockets can be made deeper in both casehalves if needed too...Setting the bearings an extra thousandth or two on each side will help out a lot....

Im sure you heard it before but....Theres like 10-12 different engine manufacturers so there will be a who slew of differences as you rip into different engines....

I once ripped apart 7 different engines and out of all 7 took bits and pieces from each and made an engine that was quite impressive for a well planned for but slapped together engine...….LOL


I even bought one straight up...It was 40cc and the kid who was selling it advertised it as a 40mph pocketbike….I asked him to show me how it hits 40mph....He had a 7/55 gearing on it aswell as a stock 40cc engine with just the stinger cut off and low n behold it did indeed hit the 40mph mark..

Best part was I got it for only $25 bucks too...He wanted $40…..LOL



I know the brands of the engines and the types of cylinders to start out with too but these days its hard to know who sells them anymore so its alot easier to buy 2-3 $80 stock engines from 3 different sellers then rip them all down sum up the parts as far as weights n balances also ports in degrees,squishbands, parts weights, crankcase volumes etc and build a really nice one.....LOL

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Last edited by CAM2; 12-27-2019 at 08:52 PM.
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Re: Case Gaskets?

If you fly cut the inner case halves, I would take the same amount off each side like .010" ( .25mm ), which will take off .020" total, .038" minus .020" is .018" clearance.

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Re: Case Gaskets?

Quote:
Originally Posted by pntrbl View Post
Figured out I was mis-reading my depth indicator yesterday. Instead of a satin finish it's a shiny thing and that makes it hard to see the lines in all that glare. I busted out with the magnifying glass today and got that straightened out. The case is 1.176 between the bearings so with a wider crank at 1.187 it's gonna bind.


I took a look at the crank too like CAM suggested and I think I may have tweaked the crank when I sucked the cases down over it. It was 1.187 at the pin and .007 shorter on the other side. Like it got squeezed? A wedge with a calibrated hammer fixed that and it was all good on the V-blocks. Under a thou.


With some .018 business card stuck in there to simulate a gasket it went together just fine. All's well. No bind. It just needs a gasket.


Still having trouble measuring the assembled clearance with a feeler gauge tho. It's like my hand gets in the way of the light and I can't see if I'm pokin' it in the right spot. I'll keep workin' on it.


Having all that under my belt I started looking at the 3rd port motor I'm planning on using. For some reason it has an extra 5 thou of clearance in one of the case halves. And a skinny crank! Together they worked out to having .002 of clearance and whaddaya know? That one bolted up without a gasket simulator and spins freely too



Something else I noticed is my fat crank has .009 of sideplay at the rod bearing. That's easy to measure with a feeler gauge. Meanwhile, Mr. Skinny has .019! These things are all over the map.


I'm gonna wait until I get some deep groove bearings pressed in to see where I'm at, but if I have to I could squeeze that skinny crank another 10 thou. It just means making stops that are .010 shorter and a push on the press. We'll see.



Obviously I'm gonna have to stumble thru this myself, but the benefit of all of the experience you guys bring to bear is a huge help. Thank You.

What you call a stumble through is a good start for a novice but theres actually a process to follow to building a proper 2 stroke engine.....One part is to never utilize a full circle crank into and reed inducted engine where the mix has to pass through the crankcase and be interferred by the crank rod...You reduce the fuel you might aswell as reduce the cc's too and go with a 36mm piston and cylinder from a NB350 2 stroke engine to compensate for the loss in properly atomized air/fuel mix needed to make power.......

Its kind of like determining the right aftermarket camshaft and carburetor for a hotrod build....

Whats funny is when you start to build a 2 stroker you start with the crank...You check its trueness aswell as its balance with its counterparts chosen to be used with the crank as an untrue crank will be falsely balanced if not trued-up first..30% of the harsh engine vibes produced are actually from untrue cranks...…..

Even the counterweights on the crank can be modified too......This is my turbo crank mod...…



I doubt that you bent the crank tightening the casehalves as they are really fragile and would've cracked or warped the casehalves or left a defined mark on both casehalves also to mention the casehalves would of been forced together in such a fashion it would've been noticed quite easily that something wasn't right unless there was some other stimulation involved curving proper judgement...LOL.

Even EPR with his bombproof billet casehalves couldn't bend his crank and couldn't get it to force the gap closed either and he definitely left marks inside the jug halves too...……..

90% of the cranks Ive come across in my building of over 120 Chinese engines in the last 10+ years as a member here had to be trued-up before balancing...

Some cranks even had to be trashed and replaced...........LOL

Another point to touch upon is the slight waiverances of differences in strokes too...…

An IE40 crank should be matched up with a 40mm piston 10mm pin

An IE44 crank should be matched up with a 10mm pin 44mm piston

An IE44HD crank should be matched with a 44mm 12mm pin piston

If you put 5 different IE40 , IE44 or IE44hd cranks on the scale and weigh the 5 of each 5 cranks for each classification will be different weights but look the same..

Same goes for the weights between the rings , wristpins and wristpin bearings too...





Sometimes you can get some parts that weigh more or less and that can play into interesting engine combos with ultra light fully balanced rotational assemblies capable of revving over 14k rpm's...

After you match up the parts then true them up and balance them that's where the amount of piston material should be removed to lighten the piston to bring the engine into the proper balance factor...

Then you blueprint the assembly to reduce turbulence polish key parts to enhance throttle response and port/widen key areas also add extra boost port channels to enhance more power...…….

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Last edited by CAM2; 12-29-2019 at 01:37 PM.
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post #19 of 21 (permalink) Old 12-29-2019 Thread Starter
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Re: Case Gaskets?

I'm listening CAM. My skinny crank has 44-6 cast in the rod and a 12mm wrist pin. Would that be an HD?


My wider crank has LX, whatever that means, and 12mm pin too.


How do you balance BTW? Do I get to build a balancing stand?
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