Go Back   DIY Go Kart Forum > Building Plans And Advice > Engines & Clutches

Notices

Closed Thread
 
Thread Tools Display Modes
  #1  
Old 06-04-2012, 03:15 AM
landuse's Avatar
landuse landuse is offline
Moderator
 
Join Date: Nov 2010
Location: Pietermaritzburg, South Africa
Posts: 17,465
Thanks: 2,192
Thanked 3,499 Times in 2,855 Posts
Default My first engine teardown/rebuild

Hi all. As most of you know (I think), I have never torn into an engine to try and rebuild it.

I have a Yamaha MZ175 5.5HP engine that I have started tearing into. It has never wanted to start since I got it, so I want to clean it up, open it up and check everything as well. This is going to be a learning experience for me, so all the help you can give will be appreciated. The person I bought it from kept it in the garage near the dogs, so there is a lot of dog hair all over the engine.

The carb on the engine is a problem. The main jet in the bowl has stripped the bowls threads, so fuel just runs out there. The engine has spark, as well as compression, so those factors are OK.

I will probably need new gaskets for everything. I will try make cereal box gaskets as a first try, and if they don't work I will get proper gaskets. I took the cover that says OHV off to have a look at the rockers (please forgive me if I don't know the proper names of stuff). Is there supposed to be a gasket for this cover as well?

What I have done already is basically fist take things apart and crack open the engine. The internals look OK to my untrained eye (nothing has exploded), but I suppose we will see as we go along. I still have to take the flywheel off. It has loads of surface rust, but I will sort that out as I go along.

I am hoping that this can maybe become a general help thread for other noobs that are cracking into an engine for the first time

I am posting a whole bunch of pics of what I have done already. You can see the governor internals, which I will probably leave as they are, as well as all the other interesting things in the block

Please could people also tell me what essential tools are needed for this type of teardown. Please give the essentials, and not just the nice to have tools. I know I will need a torque wrench, but I am not too sure of what else.
Attached Thumbnails
02062012964.jpg   02062012967.jpg  

02062012966.jpg   02062012968.jpg  

03062012974.jpg   03062012975.jpg  

03062012976.jpg   03062012977.jpg  

03062012979.jpg   03062012980.jpg  


Last edited by landuse; 08-20-2012 at 05:56 AM.
  #2  
Old 06-04-2012, 04:24 AM
OzFab's Avatar
OzFab OzFab is offline
Senior Member
 
Join Date: Nov 2011
Location: Warwick Qld, Australia
Posts: 15,619
Thanks: 1,135
Thanked 3,399 Times in 2,676 Posts
Smile

Good on you for finally taking the plunge; you won't regret it.

You'll need a decent set of sockets to go with the torque wrench. You will also need feeler guages to reset the rockers & a ring compressor (if you intend to go "all the way").

Cereal box gaskets should work for most gaskets but there are exceptions: head gasket (obviously) & side cover (this has to be a specific thickness so the crank doesn't bind or ends up sloppy). Carby gasket too, maybe.

The fact that you have compression is a good thing but, don't let it fool you. If the bore is scored you will still have compression but it will be doing damage; you'll be able to tell when you get to the real internals (no, you haven't yet)

As far as everything else goes: yes, everything looks great; that engine hasn't done much work at all.

Back to basics: IMO your carby has been your problem all along.
An engine only needs 3 things to make it work: compression, spark (you have them) & fuel (that you don't have). You mentioned that you carby is damaged: if you can repair it, great. If not, start looking for a replacement.

Good luck with it, keep us posted & if you need any help, let me know
__________________
2013 Build-off Winner - http://www.diygokarts.com/vb/showthread.php?t=21076
  #3  
Old 06-04-2012, 05:15 AM
Doc Sprocket's Avatar
Doc Sprocket Doc Sprocket is offline
*********
 
Join Date: Jun 2009
Location: Ontario, Canada
Posts: 15,677
Thanks: 723
Thanked 2,205 Times in 1,693 Posts
Default

It does sound like the carb body is shot. You shouldn't have too much trouble finding a replacement, it looks like another GX knockoff. Too bad you're so far away (I have a spare).

You may actually get away with the cereal box gasket for the side cover. Try it. One, it'll be good practice. Two, it may end up being an acceptable thickness. Since you don't have a means of measuring crankshaft endplay, put the gasket in and torque the bolts to spec. With the spark plug out, see if you can turn the crank freely by hand, and see if the crank moves in and out any appreciable distance. Should not be much if any.

I've been making my own gaskets for years. I strongly recommend you get yourself a set of leather punches for this. They are hollow steel punches with a sharp edge, and are brilliant for punching out the bolt holes in your gaskets. Perhaps after work I will post a pic of mine.

Back to torquing bolts- any chance you have a service manual? If you don't we will examine your engine further- you can probably use the honda GX160 manual to get your specs. Cheers!
__________________
Treat it as you would an aircraft frame and you should have no problems. -Name Withheld
The Manual- "Just the manufacturer's opinion of how to put this together."- Tim "The Tool Man" Taylor
Put down the wrench, and come out with your hands up!- Me!
Wrench, Wheel, Wreck, Repeat...
  #4  
Old 06-04-2012, 06:52 AM
landuse's Avatar
landuse landuse is offline
Moderator
 
Join Date: Nov 2010
Location: Pietermaritzburg, South Africa
Posts: 17,465
Thanks: 2,192
Thanked 3,499 Times in 2,855 Posts
Default

Quote:
Originally Posted by Fabroman View Post
You'll need a decent set of sockets to go with the torque wrench. You will also need feeler guages to reset the rockers & a ring compressor (if you intend to go "all the way").

As far as everything else goes: yes, everything looks great; that engine hasn't done much work at all.

Back to basics: IMO your carby has been your problem all along.
An engine only needs 3 things to make it work: compression, spark (you have them) & fuel (that you don't have). You mentioned that you carby is damaged: if you can repair it, great. If not, start looking for a replacement.
Thanks Fabroman. I am hopefully going to be getting a torque wrench soon, and I do have a decent set of sockets. I am also going to get a feeler gauge soon.

I am glad you agree with me that nothing looks too bad in there, but I still have to get to the REAL internals

Quote:
Originally Posted by toystory_4wd View Post
It does sound like the carb body is shot. You shouldn't have too much trouble finding a replacement, it looks like another GX knockoff. Too bad you're so far away (I have a spare).

You may actually get away with the cereal box gasket for the side cover. Try it. One, it'll be good practice. Two, it may end up being an acceptable thickness. Since you don't have a means of measuring crankshaft endplay, put the gasket in and torque the bolts to spec. With the spark plug out, see if you can turn the crank freely by hand, and see if the crank moves in and out any appreciable distance. Should not be much if any.

I strongly recommend you get yourself a set of leather punches for this. They are hollow steel punches with a sharp edge, and are brilliant for punching out the bolt holes in your gaskets. Perhaps after work I will post a pic of mine.

Back to torquing bolts- any chance you have a service manual? If you don't we will examine your engine further- you can probably use the honda GX160 manual to get your specs. Cheers!
Thanks Toystory. I have a feeling that the carb is going to cost me a packet. They are hard to get here for cheap. I will see if I can maybe just get a second-hand bowl and jet. The jet looks like it has also been bent (it must have taken a huge hit).

I know what you are talking about when you say leather punch. My father use to use one all the time.

Regarding a shop manual...I was going to ask if anyone was able to point me in the direction of one. I have googled myself to death.

If you say that a GX160 should be the same. Would the specs attached for the GX160 be about right?
Another question now. Where do I go from here?? What do I remove next?? Keep in mind I don't have a torque wrench or feeler gauge yet
Attached Thumbnails
torque_specs.jpg  
  #5  
Old 06-04-2012, 11:44 AM
OzFab's Avatar
OzFab OzFab is offline
Senior Member
 
Join Date: Nov 2011
Location: Warwick Qld, Australia
Posts: 15,619
Thanks: 1,135
Thanked 3,399 Times in 2,676 Posts
Default

Quote:
Originally Posted by toystory_4wd View Post
You may actually get away with the cereal box gasket for the side cover. Try it. One, it'll be good practice. Two, it may end up being an acceptable thickness.
Hey, I didn't say it wouldn't work, just that it might not be 100%

Quote:
Originally Posted by landuse View Post
Another question now. Where do I go from here?? What do I remove next?? Keep in mind I don't have a torque wrench or feeler gauge yet
Next thing to do is remove the head & check the bore.
You won't need a torque wrench or feeler guages until you start putting it back together so go for it!
__________________
2013 Build-off Winner - http://www.diygokarts.com/vb/showthread.php?t=21076
  #6  
Old 06-04-2012, 01:29 PM
landuse's Avatar
landuse landuse is offline
Moderator
 
Join Date: Nov 2010
Location: Pietermaritzburg, South Africa
Posts: 17,465
Thanks: 2,192
Thanked 3,499 Times in 2,855 Posts
Default

Do I have to remove the rockers, and whatever is underneath, before I take the head off?
  #7  
Old 06-04-2012, 01:54 PM
B man's Avatar
B man B man is offline
Tecumseh FTW!
 
Join Date: Jan 2011
Location: Oliver springs,Tn
Posts: 2,490
Thanks: 32
Thanked 98 Times in 93 Posts
Default

Cool. its a Yamaha. didn't know they made Go kart Engines.
__________________
If it doesn't work......well then its gonna!
  #8  
Old 06-04-2012, 03:50 PM
Doc Sprocket's Avatar
Doc Sprocket Doc Sprocket is offline
*********
 
Join Date: Jun 2009
Location: Ontario, Canada
Posts: 15,677
Thanks: 723
Thanked 2,205 Times in 1,693 Posts
Default

Landuse- I think you'll be safe with those torque values. Lemme do some digging around for a manual, I'll see what I can do.
__________________
Treat it as you would an aircraft frame and you should have no problems. -Name Withheld
The Manual- "Just the manufacturer's opinion of how to put this together."- Tim "The Tool Man" Taylor
Put down the wrench, and come out with your hands up!- Me!
Wrench, Wheel, Wreck, Repeat...
  #9  
Old 06-05-2012, 12:55 AM
landuse's Avatar
landuse landuse is offline
Moderator
 
Join Date: Nov 2010
Location: Pietermaritzburg, South Africa
Posts: 17,465
Thanks: 2,192
Thanked 3,499 Times in 2,855 Posts
Default

Quote:
Originally Posted by landuse View Post
Do I have to remove the rockers, and whatever is underneath, before I take the head off?
I just want to make sure of my sequence of teardown. Should I take the rockers off/out first

Quote:
Originally Posted by toystory_4wd View Post
Landuse- I think you'll be safe with those torque values. Lemme do some digging around for a manual, I'll see what I can do.
Thanks Toystory. I have been googling myself to death trying to find something. There is not a whole lot on these engines. Maybe someone else can google better than I can
  #10  
Old 06-05-2012, 06:48 AM
r_chez_08's Avatar
r_chez_08 r_chez_08 is offline
Should be in the shop...
 
Join Date: Jan 2009
Location: Cornwall, UK
Posts: 4,827
Thanks: 182
Thanked 313 Times in 308 Posts
Default

Yes landuse!!!
You have ratio rockers- I wondered which motor the gx200 stamped performance ratio rockers came from, now I know!
You should not need to remove the rockers from the head, just roll the engine over to TDC (top dead centre) and undo the bolts holding the head on.

I have a genuine gx160 carby and some clone ones that may fit, measure the distance between the two mounting studs and I will tell you. You would have to pay me for this carb though if you wanted it

Good luck buddy, get yourself a torque wrench (I reccomend a 3/8" one, because 1/2" is too big for lots of things and 1/4" is too small for lots of things)
Also, I recommend you get a gasket set. Up to you. Yes there should be a rubber or cork gasket under the rocker cover
__________________
My process of thought:
Anyone can drive a fast car, few can drive a car fast.
  #11  
Old 06-05-2012, 07:11 AM
fowler's Avatar
fowler fowler is offline
Senior Member
 
Join Date: Nov 2009
Location: Bullsbrook West Aus
Posts: 5,463
Thanks: 71
Thanked 506 Times in 441 Posts
Default

National tool warehouse. com

Have good prices on tools

For those interested Precision Instruments are very good for a good price
They are the ones snap on slaps there name on and triples the price
__________________
That's not an oil leak
It's horsepower sweat
The Following User Says Thank You to fowler For This Useful Post:
landuse (06-05-2012)
  #12  
Old 06-05-2012, 07:23 AM
landuse's Avatar
landuse landuse is offline
Moderator
 
Join Date: Nov 2010
Location: Pietermaritzburg, South Africa
Posts: 17,465
Thanks: 2,192
Thanked 3,499 Times in 2,855 Posts
Default

Quote:
Originally Posted by r_chez_08 View Post
Yes landuse!!!
You have ratio rockers- I wondered which motor the gx200 stamped performance ratio rockers came from, now I know!
You should not need to remove the rockers from the head, just roll the engine over to TDC (top dead centre) and undo the bolts holding the head on.

I have a genuine gx160 carby and some clone ones that may fit, measure the distance between the two mounting studs and I will tell you. You would have to pay me for this carb though if you wanted it

Good luck buddy, get yourself a torque wrench (I reccomend a 3/8" one, because 1/2" is too big for lots of things and 1/4" is too small for lots of things)
Also, I recommend you get a gasket set. Up to you. Yes there should be a rubber or cork gasket under the rocker cover
Thanks R_chez. So I leave the rockers as they are, get the piston to TDC, and then undo the head bolts. You say that there should be a gasket under the rocker cover. I had better get one. It looks like the guy who had the engine before me just used silicone sealant. I had to peel it off.

I will post some pics when I get the head off. Will anything fall out when I take the head off. There are things like pushrods and lifters in there, I know that.
  #13  
Old 06-05-2012, 08:37 AM
landuse's Avatar
landuse landuse is offline
Moderator
 
Join Date: Nov 2010
Location: Pietermaritzburg, South Africa
Posts: 17,465
Thanks: 2,192
Thanked 3,499 Times in 2,855 Posts
Default

I also found these torque values on AGK's website. Which ones do you think are best?
Attached Thumbnails
torque.jpg  
  #14  
Old 06-05-2012, 08:49 AM
r_chez_08's Avatar
r_chez_08 r_chez_08 is offline
Should be in the shop...
 
Join Date: Jan 2009
Location: Cornwall, UK
Posts: 4,827
Thanks: 182
Thanked 313 Times in 308 Posts
Default

Yeah I would say those torque values should be close. Nothing should fall out when you take the head off. Be careful if you wish to reuse the head gasket- they may be hard to come by.
What you can also do to approximate torque values is use a torque wrench to undo the bolts, and slowly increase the torque on the micrometer scale until the bolt breaks loose without the wrench clicking. This may be off though depending if the previous owner had the motor apart and did not use a torque wrench for reassembly.

Btw- the spacing on the gx160 carbs is approx. 42mm
__________________
My process of thought:
Anyone can drive a fast car, few can drive a car fast.
  #15  
Old 06-05-2012, 08:51 AM
fowler's Avatar
fowler fowler is offline
Senior Member
 
Join Date: Nov 2009
Location: Bullsbrook West Aus
Posts: 5,463
Thanks: 71
Thanked 506 Times in 441 Posts
Default

most torque wrenchs get damaged by undoing a bolt?
__________________
That's not an oil leak
It's horsepower sweat
  #16  
Old 06-05-2012, 08:57 AM
landuse's Avatar
landuse landuse is offline
Moderator
 
Join Date: Nov 2010
Location: Pietermaritzburg, South Africa
Posts: 17,465
Thanks: 2,192
Thanked 3,499 Times in 2,855 Posts
Default

Quote:
Originally Posted by r_chez_08 View Post
Yeah I would say those torque values should be close.
I have posted 2 sets of torque values. One from a GX manual, and the other from AFG's website. Which one looks the best.

AFG says 17 for the head bolt, and the manual says 24. There are some others also different.

How big are these differences in reality?
  #17  
Old 06-05-2012, 09:18 AM
r_chez_08's Avatar
r_chez_08 r_chez_08 is offline
Should be in the shop...
 
Join Date: Jan 2009
Location: Cornwall, UK
Posts: 4,827
Thanks: 182
Thanked 313 Times in 308 Posts
Default

I would go for the gx manual. If you can find your yamaha manual, great, because this is definently not a clone. Maybe inspired by a Honda but not the same.
I reckon the motor may not have done a lot of work. The previous owner probably tried to clean the carb after putting dirty fuel in it, and in the process stripped the thread. Then left it because they couldn't be bothered/ didn't know how to fix it.

IMO, I would completely strip down the motor, and learn as much as you can in the process. Then reassemble, replacing anything worn or damaged, cleaning everything and applying oil or assembly grease to any surfaces that touch. Depending on the age, you may want to replace the piston rings while you are in the motor.
If you cannot find the manual, just use a gx160 manual. The specs cannot be far out for torque and clearances.
__________________
My process of thought:
Anyone can drive a fast car, few can drive a car fast.
The Following User Says Thank You to r_chez_08 For This Useful Post:
landuse (06-05-2012)
  #18  
Old 06-05-2012, 09:57 AM
Brandon1023's Avatar
Brandon1023 Brandon1023 is offline
needs an oil change
 
Join Date: Nov 2011
Location: Miami, Florida, Dade County 305
Posts: 419
Thanks: 24
Thanked 14 Times in 13 Posts
Default

I think you can get away with skimping on certain bolts. Probably not the best advice to be preaching, but I fix a couple mowers a week and I don't worry about the torque ratings as much as I should. Anyway, the bolts on say.. the shroud, don't need to be stressed as much as the bolts on the cylinder head, for example. I've yet to see a problem which constitutes removing the head.

As for the other bolts, I just give them a good snug tightening. Obviously, there's a medium somewhere. You don't want the bolt to twist and unscrew with engine vibration, and on the other hand, you don't want the bolt to strip the thread in the hole, or on the bolt itself.

Also something I know for certain is that you need to be careful when it comes to the crankcase gasket. If it's too thin or too thick, the crankshaft will be off balance and engine harmonics (dangerous vibration disturbances within the engine) can render your engine completely trashed. If not balanced, the crankshaft and twist as much as 5 degrees per power cycle. This is a lot when you think about a solid, forged crankshaft which seems as though nothing can break it. Just some thought.
  #19  
Old 06-05-2012, 11:29 AM
OzFab's Avatar
OzFab OzFab is offline
Senior Member
 
Join Date: Nov 2011
Location: Warwick Qld, Australia
Posts: 15,619
Thanks: 1,135
Thanked 3,399 Times in 2,676 Posts
Default

Wow, you're getting quite a following.

That's all very useful information, did you get it all?

Yes, there will be pushrods below the head but they shouldn't fall out unless you're working upside down (lol).

Silicone or silastic is often used to replace cork gaskets, after all, the only thing they do is keep the oil inside the engine.

What are your torque values in: Nm or ft/lb? There will only be one or two places where torque setting will be critical (big end for instance), too loose & the bolts/nuts will work looser, too tight & you may get some binding.

Remember, if you're not sure, look it up or ask; there are no silly questions
__________________
2013 Build-off Winner - http://www.diygokarts.com/vb/showthread.php?t=21076
  #20  
Old 06-05-2012, 12:53 PM
r_chez_08's Avatar
r_chez_08 r_chez_08 is offline
Should be in the shop...
 
Join Date: Jan 2009
Location: Cornwall, UK
Posts: 4,827
Thanks: 182
Thanked 313 Times in 308 Posts
Default

I would reccomend torquing any bolt going into an aluminium thread. I have stripped two on my gx160 shroud, I didn't even do them up that tight. I need to helicoil or keensert them now.

However, the only ones that are critical are the rod bolts and flywheel nut, as these can cause severe failure. I would also torque the side cover bolts because if you undertorque them they are likely to loosen and oil will leak. If you don't notice you can stuff the engine.
__________________
My process of thought:
Anyone can drive a fast car, few can drive a car fast.
Closed Thread

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off



All times are GMT -6. The time now is 07:13 PM.