Boatmad.com


Reply
 
Thread Tools Display Modes
 
Old 11-07-2012, 10:40 PM   #1
Registered User
 
paddy the phantom's Avatar
 
Country: Ireland
Boat name: Lilly the Pink
Boat make: Phantom 21
Engines: XR2 200

Join Date: Aug 2010
Posts: 82
merc 2.5 issues

Hi Folks,

First of all sorry for the long post!!!!
Looking for some help if anyone has any ideas. I recently rebuilt a 2.5 200 merc carb,running wh 46 with mains jetted on 90s ,poppet removed ,thermostats removed,oil cooler removed and oil block off kit used ,left plastic oil pump on crank , restrictors in heads ,1 piece exhaust divider ,new water impeller ,with a set of forged wizard pistons ,balanced lightened rods and wrist pins and sps bolts from JSRE ,full set of seals, big ends, rings,heads clipped to 34cc ,dual stage boysen 4 petal reeds.The machine shop worked the sleeves to 8 thou over ,nice and round , Running an electric fuel pump through the mechanical oem at 5psi with no restrictions in hose .Exhaust and front half are standard .
Set timing at 25 degrees.

Fuel at 32:1 on a blend of oil , compression all within 2-3 ibs of each cylinder starting from 145-148ibs ,Engine run for 9 hours at 1 hour at a time ,then full cool down . Brought her out and ran it in slow,she was a little tight low down under 3k rpms ,with a quick run up to 5k rpm for a couple of seconds ,number 2 detonated and locked up,head temp was very hot 170 plus within seconds

Rebuilt engine again with a cheaper new forged Wiesco piston ,until I found the problem ,rebuilt all carbs,checked all the floats and reset them ,cleaned and checked needles ,seats and gaskets , increased main jets to .98,removed electric fuel pump and ran stock pump,changed fuel for new petrol.
Ran the engine again very,very slowly 1500rpm,2000rpm,2,500 etc up to 4500rpm over 4 hours ,again number 2 detonated .
Spent 2 hours setting the engine timing,but this time at 23 degrees.

On both occasions the exhaust port side of the piston is melting ,still retaining the rings,it is definatley getting enough fuel based on the how wet the cyclinders are .

Now for the third attempt,using a used cast Art piston this time ,changing carbs around putting top set of carbs in middle feeding cyclinder 3 and 4 ,and middle set of carbs feeding cyclinder 1 and 2,also changing head gaskets and putting stock 41cc heads on to lower compression with a colder plug .
And reset the timing to 20 maybe,havent run it yet ,hopefully next week.

If any one has any further suggestions i would be very grateful at this stage,starting to lose patience with this.

Thanks very much.
__________________

__________________
Paddy the Phantom
paddy the phantom is offline   Reply With Quote
Old 11-07-2012, 11:01 PM   #2
Registered User
 
Country: england
Location: the grim north
Occupation: robot
Cruising area: tyne

Join Date: Nov 2004
Location: the grim north
Posts: 905
Do you not need more piston clearance on a steel bore motor when running forged pistons .due to the fact it does not dispesre heat like the ni-com race engines.
__________________

__________________
Speed costs weight so what do we cut off first
sinkunit0 is offline   Reply With Quote
Old 11-07-2012, 11:52 PM   #3
Registered User
 
maz928's Avatar
 
Country: England
Location: Poole
Interests: Boats/cars
Boat make: Boss 21/Argentinian HotBoat
Engines: Mercury 2.5 Offshore
Cruising area: Poole/Solent

Join Date: Jul 2007
Location: Poole
Posts: 292
I would check out the stator,check timming not only on number 1 cylinder
but all six as you may find number 2 is over advancing.
Ive had this a few times on merc stators and now always check all six cylinders.Once you've marked the flywheel its really quick to check each cylinder.
maz928 is offline   Reply With Quote
Old 12-07-2012, 02:03 PM   #4
Registered User
 
paddy the phantom's Avatar
 
Country: Ireland
Boat name: Lilly the Pink
Boat make: Phantom 21
Engines: XR2 200

Join Date: Aug 2010
Posts: 82
Merc issues

Thanks Mate,

Agreed was thinking this myself ,got some good advice on the forged piston clearance required from JSRE ,Hutchy and a few other all agreed a min of 8 thou and ring gap over 18thou. was thinking with Irelands tropical climate the water temp could be causing some cold seizing .
The only saving grace at this stage is the cyclinder has been honed out twice so its closer to 9 thou plus over,it was sloppy at 8 thou,9 thou plus is a little scary when cold!


Thanks for the advice.
__________________
Paddy the Phantom
paddy the phantom is offline   Reply With Quote
Old 12-07-2012, 02:06 PM   #5
Registered User
 
paddy the phantom's Avatar
 
Country: Ireland
Boat name: Lilly the Pink
Boat make: Phantom 21
Engines: XR2 200

Join Date: Aug 2010
Posts: 82
stator

Quote:
Originally Posted by maz928 View Post
I would check out the stator,check timming not only on number 1 cylinder
but all six as you may find number 2 is over advancing.
Ive had this a few times on merc stators and now always check all six cylinders.Once you've marked the flywheel its really quick to check each cylinder.
Thanks a million for this,this is were my money is ! I reckon it has to be the timing advanced ,I will be the first thing to be checked before its run this time on all cylinders,Jay Smith made the same comment ,or double firing.

Thanks very much
__________________
Paddy the Phantom
paddy the phantom is offline   Reply With Quote
Reply

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
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Powered by vBadvanced CMPS v3.2.3

All times are GMT +1. The time now is 04:42 PM.


Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2019, vBulletin Solutions, Inc.
×