rebuild 90

[johnson89]

rebuild 90 ...never could get pic's to load,,,see how this works out.....this is # 3 piston,,,motor would still run....it is in about 200 parts now,and block is at machine shop....all 4 cyls have to be bored,was told the other 3 were out of specs...also got to find a head

 

[emdsapmgr]

It's also advisable to determine the reason for the failure. Hopefully before you get the new block ready for start-up. I'd start by doing an autopsy on the carb that feeds the damaged cyl. Possible the high speed jet feeding that throat is restricted, causing this lean condition.

 

[johnson89]

yes the high speed jet is perfect....that the first thing I took out...have not taken the rest of the carb. apart yet....I checked spark before I took it apart....only thing that happen was top ring broke,and put a very small scar on cyl. wall...does not look like it ever got hot,piston is clean even on the back side look's like the other pistons...only thing I notice so far was the back plate for the exhaust,the 3 bolts that were right next too this cyl.were all just hand tight,while the other bolts took a wrench to get off....

 

[emdsapmgr]

Sure looks like that piston got hot. Appears to be a lot of cyl liner scuffing in the picture. That's a lean condition. Piston rings don't usually break up for no reason. Either the cylinder was running lean on fuel or without any lubrication. Was this engine running on a VRO or on a diet of 50-1 premix fuel? Difficult to see if the other rubber water diverter is in it's correct position. If it's out of position, possible that cyl overheated from lack of cooling water flow.

 

[johnson89]

all of the rubber diverter look great....took apart all of the carbs. and every jet was clean,the carb.s were spotless.....still looking for a reason....the water pump had a steady stream

 

[glenn property of pam]

possible air leak leading to a lean condition

 

[johnson89]

the only thing I notice loose was the exhaust cover on back of motor,3 bolts down near # 3 cyl.were finger tight..i guess they worked loose after 20 plus years,unless the 1st owner maybe had done something...never did hear and alarm,I did check it about a year ago and was working at that time,will check again when I get it back together

 

[Faztbullet]

Check to see it top ring locating pin is in ring land , if missing that allows ring to rotate and catch in port and break. If this is the case the cooling system has not been maintained or has been hotttt a couple of times!!! I noticed thats not a OEM gasket as it left blue residue on block.(OEM is black). You can take a demel and clean up high spots in head and magnet to see if ring pieces have been removed as the dents will fill with carbon over time.

 

[emdsapmgr]

How about the midrange jet. Was it clear also?