| Author |
Message |
    
Damir Kralj
New member
Username: dk79
Post Number: 2
Registered: 06-2009
| | Posted on Wednesday, June 24, 2009 - 07:36 am: | 
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Hello !
After various strange issues with this engine i decided to inspect the internals , so yesterday upon removing the reed block i noticed that the piston in the 2-nd cylinder is fitted the wrong way around (as an whole assembly ,with the conrod ..) -> with the UP mark facing towards the driveshaft instead of the flywheel ..
List of strange behaviour was as follows :
1 Hard starting from cold
2 Rough idle
3 Vibrations/shaking at idle and low rmp
4 Very hard re-starting warm engine
5 Excessive exhaust smoke
6 Hesitating when accelerating from low rmp
Now , can i blame this wrongly fitted piston for all these stuff ?! as everything else on the engine was in good working order (ignition components , carburetor etc.)
Thanks !
Damir |
Fastjeff
Senior Member
Username: fastjeff
Post Number: 6096
Registered: 09-2003
| | Posted on Wednesday, June 24, 2009 - 11:01 am: |
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That'll do it. That's a looper with flat top pistons or the motor would have locked up.
Jeff |
Graham Lamb
Senior Member
Username: galamb
Post Number: 5452
Registered: 05-2007
| | Posted on Wednesday, June 24, 2009 - 11:05 am: |
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While it's not a good thing that you have an upside down piston, I don't think you can blame it solely for all the issues you note.
The motor is a standard cross flow design. The piston is basically a "flat top" so "one side" is not interfering with a intake or exhaust port.
But hey, maybe it is just the piston causing everything.
You need to split the powerhead and turn it around regardless (just because it's wrong). If issues remain, address them when you have it all back together correctly. |
Damir Kralj
Member
Username: dk79
Post Number: 4
Registered: 06-2009
| | Posted on Wednesday, June 24, 2009 - 11:50 am: |
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Hi !
Well , yes the piston crowns are flat but i noticed that each piston has some kind of ports on the piston skirt ( two ports on each side separated into two sections .. so 4 ports/passages on each piston precisely !) and also cuts on the lower ends of the piston skirt , and , if i understand this , this ports/cuts on the piston must be matched "mirror image" with the cylinder bore ports and if the piston is turned with the UP towards the driveshaft these thins dont quite match up .. and , by rough examination with opened exhaust cover looks like the ends of piston rings where rubbing onto the exhaust port area as well which looks/sound like bad news as well... will tear the powerhead apart tonight and inspect more throughly but i do not fancy using this powerhead again !
Anyway , i have a spare one from early '80 merc 25 which had blue decals (mine has brown) and this powerhead was in good working order so will just re-fresh it a little bit and bolt it on as an replacement .
Thanks for info Jeff/Graham !
Regards
Damir |
Fastjeff
Senior Member
Username: fastjeff
Post Number: 6104
Registered: 09-2003
| | Posted on Wednesday, June 24, 2009 - 03:19 pm: |
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.."The motor is a standard cross flow design. The piston is basically a "flat top" so "one side" is not interfering with a intake or exhaust port. "
I think the Great One got his loopers and crossflow designs confused.
Jeff |
Damir Kralj
Member
Username: dk79
Post Number: 5
Registered: 06-2009
| | Posted on Wednesday, June 24, 2009 - 04:15 pm: |
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If it was crossflow design it'll have domed pistons right ?
Anyways , heres a few pic of the pistons and engine block :
Piston
http://www.uploadhouse.com/viewfile.php?id=4194497
http://www.uploadhouse.com/viewfile.php?id=4194498
http://www.uploadhouse.com/viewfile.php?id=4194499
Block
http://www.uploadhouse.com/viewfile.php?id=4194504
http://www.uploadhouse.com/viewfile.php?id=4194506 |
Damir Kralj
Member
Username: dk79
Post Number: 6
Registered: 06-2009
| | Posted on Wednesday, June 24, 2009 - 04:16 pm: |
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Jeff , what do you reckon should i replace this piston or just clean it ?! :
http://www.uploadhouse.com/viewfile.php?id=4194512
http://www.uploadhouse.com/viewfile.php?id=4194513
.. as it haves some strange gray spots on the skirt .. but it's not scored ..
Thanks !
Damir |
Fastjeff
Senior Member
Username: fastjeff
Post Number: 6110
Registered: 09-2003
| | Posted on Wednesday, June 24, 2009 - 07:26 pm: |
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Just clean it up.
Do those holes above the piston pin go thru?
Jeff |
Damir Kralj
Member
Username: dk79
Post Number: 7
Registered: 06-2009
| | Posted on Thursday, June 25, 2009 - 11:27 am: |
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No , it just looks like that ! this the holes above the pins didn't break trough the piston skirt on the other side .. also , i've tried to rock/move/push the piston pins an they're solid/tight fit so that's fine as well ..
Thanks for help Jeff !
Regards
Damir |
Graham Lamb
Senior Member
Username: galamb
Post Number: 5463
Registered: 05-2007
| | Posted on Friday, June 26, 2009 - 01:47 am: |
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Yes, Jeff, did get them confused - was thinking flat top and domed and half domed pistons while answering also an email about an early 90's Force at the same time (explaining that CFI was just a cool sticker that meant it used "old" cross flow design which really wasted gas).
Getting too old to try and do two things at once  |
Fastjeff
Senior Member
Username: fastjeff
Post Number: 6131
Registered: 09-2003
| | Posted on Friday, June 26, 2009 - 03:58 am: |
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You still do them better than most other people!
Jeff |
