| Author | Topic |
|---|
Location:
The Central Coast
Registered:
October 2002
|
|
Re: Advice on what i should do here.
|
Wed, 23 October 2002 03:16
 
|
 |
There is two types of piston crack that I have some info on from a book I got from a German piston manufacturer: Kolbenschmidt.
~~~~~~~~~~~~~~~~~~~~~~~
1. Piston fractures due to contact between piston crown and cylinder head.
Assessment
The hard impacts between the piston crown and cylinder head cause such sever piston vibration that cracks develop extremely rapidly, preferentially in the skirt region. In the case of pistons with an oil control ring below the piston pin, this nearly always results in skirt breakage in the region of the lower oil ring groove.
Possible causes
1. The clearance between the piston crown and cylinder head at the top dead centre was too small. Caution: pisonts with diameter of about 120mm grow towards the cylinder head in operation by some tenths mm due to the differing thermal expansion of the moving parts and the cylinder block.
2.The cylinder head gasket must ahve the specified thickness.
3.Connecting rod bearings which have excessive clearnace or are worn out, especially in conncetion with over-revving when running downhill
2.Piston fractures in the pin boss.
Assesment
Boss cracks occur due to overload and are favoured by shortage of oil in the pin bearing. A pin boss crack which was initiated by overload then continues to spread under normal loading and finally leads to cleavage of the piston.
Possible causes
1.Combustion irregularities, especially hard combustion due to ignition delay
2.Excessive or inappropriate use of starting aids for cold starting
3. The cylinder has filled with water or guel whilst the engine was not operated (water or fuel lock.)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
So yeah, if the piston is cracked, yes you're right, the motor is stuffed.
One thing to remember, if you're going to fix the motor, you don't want the same problem happening twice, so check oil and make sure you're carby's choke system is working properly to supply fuel at cold start. Anything other than that, it's a combination of buildups and stresses over the years, combining with bad luck.
If you don't have the money, don't spend more than what is necessary. Just fix the 7AFE for now, wait until you aren't so far in debt and do a conversion in a couple of years time when you can ACTUALLY afford it.
[Updated on: Wed, 23 October 2002 03:16]
|
|
|
| | Subject | Poster | Date |
|---|
 |
Advice on what i should do here.
|
HyEnA^ | Tue, 22 October 2002 13:16 |
|
Re: Advice on what i should do here.
|
Remedy | Tue, 22 October 2002 23:19 |
|
Re: Advice on what i should do here.
|
HyEnA^ | Wed, 23 October 2002 00:22 |
|
Re: Advice on what i should do here.
|
Sprocket | Wed, 23 October 2002 02:40 |
|
Re: Advice on what i should do here.
|
HyEnA^ | Wed, 23 October 2002 02:51 |
|
Re: Advice on what i should do here.
|
Sprocket | Wed, 23 October 2002 04:39 |
|
Re: Advice on what i should do here.
|
Sprocket | Wed, 23 October 2002 03:16 |
|
Re: Advice on what i should do here.
|
HyEnA^ | Wed, 23 October 2002 04:18 |
|
Re: Advice on what i should do here.
|
Sprocket | Wed, 23 October 2002 04:24 |
|
Re: Advice on what i should do here.
|
AE82TwinCam | Wed, 23 October 2002 04:36 |
|
Re: Advice on what i should do here.
|
HyEnA^ | Wed, 23 October 2002 06:34 |
|
Re: Advice on what i should do here.
|
HyEnA^ | Thu, 24 October 2002 04:30 |
|
Re: Advice on what i should do here.
|
Sprocket | Thu, 24 October 2002 04:38 |
|
Re: Advice on what i should do here.
|
HyEnA^ | Sat, 26 October 2002 00:25 |
|
Re: Advice on what i should do here.
|
Sprocket | Sun, 27 October 2002 23:54 |
