Finally got the Mack Mag built!

[Kpi890]

Picture 1 is that pitting, that speckled appearance? If so that could be from running lean or high compression I think.. The scratches on the crush ring could be a source of a leak or maybe they're not enough to cause a leak.. Can you feel them when you run your fingernail over them? If so you can spin the head on very fine wet n dry paper on glass to make concentric rings of scratches instead.

Picture 2 is the wet left side from a leak or did the oil just run over there after you loosened/ removed it? It's the stock aluminium gasket so I already hate it (prejudice lol) what is the squish gap measurement with this 0.7mm gasket? Do you have a spare, or any of the copper head gaskets?

Picture 3 are the rings in good order and correctly positioned with the gap over the locating pun in the piston? Are there any of those suspicious speckles on the piston?

Picture 4 is there any trace of the blackened oil in the crankcase or is that just a bit of scorching on the base gaskets.

I would like to see the top of the cylinder too. Also you could check inside the mag cover and the clutch cover to see if any fuel is present (from a crank seal leak) just in case.

1. The speckling wiped clean and was smooth underneath.
2. The wet left side was indeed I believe a leak and I replaced the aluminum gasket with 2 stock aluminum gaskets in an attempt to see what it does with a slightly lower compression.
3. The rings seem to be in good working order and there aren’t any speckles on the piston I could find. What would the speckles mean if there were?
4. There was some darker oil down in the crankcase, I wouldn’t call it blackened but it looked like the color of honey.

I replaced everything back on the bike with the two aluminum head gaskets just to see what it would do with lowering the compression. The bike started up just fine now but is still acting up on the throttle side of things. When I give it some throttle it’s acting like there’s an air leak but I cannot for the life of me find anything. I used a propane torch, not lit, while the bike was idling and pointed it at every crack and seal around the intake manifold and my intake tubing and all around the carb. The engine didn’t change pace at all until I put the torch near the air filter and then it bogged and died as normal when I check with propane. I pulled the magneto cover and it’s clean as a whistle in there no gas or any residue of anything.

 

[Kpi890]

And here’s some pictures of the clutch cover pulled, found some small pieces of what looks like rubber inside the bottom? Sometimes when I park the bike in the garage after running for a while I can sometimes smell either burning rubber or just hot rubber. I never see smoke but always just thought it was the spark plug boot heating up.

 

[FurryOnTheInside]

1. The speckling wiped clean and was smooth underneath.
2. The wet left side was indeed I believe a leak and I replaced the aluminum gasket with 2 stock aluminum gaskets in an attempt to see what it does with a slightly lower compression.
3. The rings seem to be in good working order and there aren’t any speckles on the piston I could find. What would the speckles mean if there were?
4. There was some darker oil down in the crankcase, I wouldn’t call it blackened but it looked like the color of honey.

I replaced everything back on the bike with the two aluminum head gaskets just to see what it would do with lowering the compression. The bike started up just fine now but is still acting up on the throttle side of things. When I give it some throttle it’s acting like there’s an air leak but I cannot for the life of me find anything. I used a propane torch, not lit, while the bike was idling and pointed it at every crack and seal around the intake manifold and my intake tubing and all around the carb. The engine didn’t change pace at all until I put the torch near the air filter and then it bogged and died as normal when I check with propane. I pulled the magneto cover and it’s clean as a whistle in there no gas or any residue of anything.

Two stock gaskets

And here’s some pictures of the clutch cover pulled, found some small pieces of what looks like rubber inside the bottom? Sometimes when I park the bike in the garage after running for a while I can sometimes smell either burning rubber or just hot rubber. I never see smoke but always just thought it was the spark plug boot heating up. View attachment 82489View attachment 82490View attachment 82491View attachment 82492View attachment 82493

I wonder what colour clutch pads are in your engine. Those are probably (hopefully!) just the pieces from the edges of the pads where they are a bit roughly stamped.
I noticed that smell too. I think the smell is from the stock exhaust gasket.. When I removed my exhaust the gasket came apart and the rubber(?) stuff was crumbly.

An extra 0.7mm stock gasket is a pretty big change. More than 1.21cc. The ideal squish gap is said to be 0.8mm. I don't really think too high compression was the problem anyway but without the figures... Anyway I guess it's okay to try it and see what you think.

Pitting in the middle of the piston crown would, to my understanding, mean detonation from too much heat (from lean a/f) and high pressure (spark firing too early or pre-ignition (hot debris in the exposed plug threads or the plug hole threads etc))

 

[Kpi890]

Two stock gaskets

I wonder what colour clutch pads are in your engine. Those are probably (hopefully!) just the pieces from the edges of the pads where they are a bit roughly stamped.
I noticed that smell too. I think the smell is from the stock exhaust gasket.. When I removed my exhaust the gasket came apart and the rubber(?) stuff was crumbly.

An extra 0.7mm stock gasket is a pretty big change. More than 1.21cc. The ideal squish gap is said to be 0.8mm. I don't really think too high compression was the problem anyway but without the figures... Anyway I guess it's okay to try it and see what you think.

Pitting in the middle of the piston crown would, to my understanding, mean detonation from too much heat (from lean a/f) and high pressure (spark firing too early or pre-ignition (hot debris in the exposed plug threads or the plug hole threads etc))

Well for now I’m going to leave the double head gaskets on there since my engine is still hot and yes it Definitely makes a difference in power compared to what it was. The head does seem to run cooler though but can’t be sure. I may just have to make a video so you can understand the throttle situation, it only bogs down once I have let go of the throttle and pull the clutch and then attempt to accelerate again. I have noticed if I don’t pull the clutch and just use the brakes to slow down enough to where the engine won’t stall and throttle it the response is great. It almost feels like with the clutch enabled it is allowing, what feels like a rich mixture, to clear out whereas if I pull the clutch I almost have to rev the engine slightly before dropping it to have the throttle response I’m after. Does that make sense? Scenario: I’m rolling down the street WOT and ahead is a stop sign so I pull the clutch ahead of time and use my brakes to slow down. Doing the normal California stop I do I don’t really ever stop completely so while still rolling I drop the clutch while simultaneously hitting the throttle. It bogs right there. Whereas if I don’t pull the clutch and just roll slowly and then hit the gas again the throttle response is much better. Oh and here’s a few pics of the bike currently so you can get a better idea of the entire setup!

 

[FurryOnTheInside]

Well for now I’m going to leave the double head gaskets on there since my engine is still hot and yes it Definitely makes a difference in power compared to what it was. The head does seem to run cooler though but can’t be sure. I may just have to make a video so you can understand the throttle situation, it only bogs down once I have let go of the throttle and pull the clutch and then attempt to accelerate again. I have noticed if I don’t pull the clutch and just use the brakes to slow down enough to where the engine won’t stall and throttle it the response is great. It almost feels like with the clutch enabled it is allowing, what feels like a rich mixture, to clear out whereas if I pull the clutch I almost have to rev the engine slightly before dropping it to have the throttle response I’m after. Does that make sense? Scenario: I’m rolling down the street WOT and ahead is a stop sign so I pull the clutch ahead of time and use my brakes to slow down. Doing the normal California stop I do I don’t really ever stop completely so while still rolling I drop the clutch while simultaneously hitting the throttle. It bogs right there. Whereas if I don’t pull the clutch and just roll slowly and then hit the gas again the throttle response is much better. Oh and here’s a few pics of the bike currently so you can get a better idea of the entire setup! View attachment 82496View attachment 82497

I am imagining that scenario and I think that when you pull the clutch and shut off the throttle the RPM slows to idle speed, but when you don't pull the clutch the RPM is kept higher than idle speed because the wheel is still cranking the engine.
It's really just that you're building up the revs from a lower point.

I experience the same thing when I restart from a low speed vs a high speed restart (I don't idle, I have deliberately set idle too low so I can use throttle and clutch to "low idle kill"), not literally a bog just that the two stroke engine doesn't start to make power until a certain RPM when it gets some flow going, enertia of the a/f or whatever magic it is that makes an engine with no valves work. A four stroke engine can start making torque sooner because of the valves but our two strokes need to be flowing.
It never bothered me that it isn't pulling very well until the RPM climbs, I pedal anyway so it doesn't take long to get up to speed.

So I guess maybe just set the idle higher. Maybe slip the clutch rather than drop it sometimes too.

 

[Kpi890]

I am imagining that scenario and I think that when you pull the clutch and shut off the throttle the RPM slows to idle speed, but when you don't pull the clutch the RPM is kept higher than idle speed because the wheel is still cranking the engine.
It's really just that you're building up the revs from a lower point.

I experience the same thing when I restart from a low speed vs a high speed restart (I don't idle, I have deliberately set idle too low so I can use throttle and clutch to "low idle kill"), not literally a bog just that the two stroke engine doesn't start to make power until a certain RPM when it gets some flow going, enertia of the a/f or whatever magic it is that makes an engine with no valves work. A four stroke engine can start making torque sooner because of the valves but our two strokes need to be flowing.
It never bothered me that it isn't pulling very well until the RPM climbs, I pedal anyway so it doesn't take long to get up to speed.

So I guess maybe just set the idle higher. Maybe slip the clutch rather than drop it sometimes too.

Wow. I am starting to realize you’re absolutely correct on that. I guess I just got so caught up in this build being perfect. That makes sense now and here I was thinking crap my throttle response should be instant lol. At this point I have confirmed I have no air leaks on the intake, exhaust, or any compression leaks. With the two head gaskets and a #61 jet it’s currently idling and running as I believe it should! This RT carb is slowly becoming a favorite in my book, the engine starts immediately and without any choke, idles amazing, and the ramp up in rpm’s is very steady, and for only $18! There is still the tiny fact that my JB weld inside my one stripped intake stud did not hold lol. It’s not leaking or anything but when I back the nut off sometimes I can see the stud move just a bit so hopefully I can figure out a better adhesive or something to keep it in there. Furry, I cannot thank you enough for your knowledge, patience, and help along the way with this situation. I truly appreciate it sir!

 

[FurryOnTheInside]

Wow. I am starting to realize you’re absolutely correct on that. I guess I just got so caught up in this build being perfect. That makes sense now and here I was thinking crap my throttle response should be instant lol. At this point I have confirmed I have no air leaks on the intake, exhaust, or any compression leaks. With the two head gaskets and a #61 jet it’s currently idling and running as I believe it should! This RT carb is slowly becoming a favorite in my book, the engine starts immediately and without any choke, idles amazing, and the ramp up in rpm’s is very steady, and for only $18! There is still the tiny fact that my JB weld inside my one stripped intake stud did not hold lol. It’s not leaking or anything but when I back the nut off sometimes I can see the stud move just a bit so hopefully I can figure out a better adhesive or something to keep it in there. Furry, I cannot thank you enough for your knowledge, patience, and help along the way with this situation. I truly appreciate it sir!

No worries, I'm glad to have something to read and reply to when I sit down for a coffee or when there's adverts on the TV
I'm very glad that you are happier with your bike too.

 

[Kpi890]

No worries, I'm glad to have something to read and reply to when I sit down for a coffee or when there's adverts on the TV
I'm very glad that you are happier with your bike too.

I absolutely love building these bikes, but man oh man when your run into something and can’t toubleshoot it right away it’s like going down the rabbit hole. Now on to the next part I can buy to increase the performance and/or style of this build! Any suggestions?

 

[FurryOnTheInside]

I absolutely love building these bikes, but man oh man when your run into something and can’t toubleshoot it right away it’s like going down the rabbit hole. Now on to the next part I can buy to increase the performance and/or style of this build! Any suggestions?

Muffler? Better brakes? 40T / 41T sprocket?

 

[Kpi890]

Muffler? Better brakes? 40T / 41T sprocket?

Muffler you aint kiddin! This pipe is like a screamin banshee. It’s not in the photo above but I have a hotdog muffler temporarily on there right now and it does help to cut noise down, but not sure how it affects performance, any mufflers you’d suggest? I do have a 36T sprocket I haven’t opened yet for this bike maybe I’ll see what that can do this weekend. I have front disc brakes and rear caliper brakes due to the sprocket, are there better brakes I could be using?