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03-25-2020, 02:55 PM #1
OMC V4 Cylinders out of round ????
Started a rebuild of a 140 OMC V4
The motor ran for a bout 3 or 4 min then blew out the possible crank / intake seems
Prior to this the motor was honed (It was bought as a seized motor)
Looking into the cylinders today i saw that 2 of them had an almost polished area on them just above the inlet port. This motor only ran for a matter of mins
What may have caused this ??? It was only 2 on the same bank almost at the same point, could it be the rings catching ????
Both pistons show no sign of damage nor do the rings (All pistons and rings are brand new)
Once i blew the photos up i also found a ding in the plating will this grow as the engine breaks in ???
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03-25-2020, 05:49 PM #2
From what i see the cylinder surface looks really bad. I see no crosshatch diamond pattern at all which is a result improper hone stroke, theres chatter marks and what looks like left over tool marks from the bore job. The ports have no chamfer at all and the polished area is usually from the bore being oversize. Was the honing done with a rigid hone ? it could just be oversize in the port area possible from too much time with a miniball or flex hone in the center of the bore.... Sorry what i see..
Last edited by H2OPERF; 03-25-2020 at 05:57 PM.
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powerabout, spybot thanked for this postracer liked this post
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03-25-2020, 06:25 PM #3
The hone job should have a flattened diamond pattern similar to this.
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spybot thanked for this post
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03-26-2020, 05:30 AM #4
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03-26-2020, 07:12 AM #5Screaming And Flying!
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03-26-2020, 07:36 AM #6
Do as he said but ur gonna probably need to find another shop, Is it standard bore? or os already? by the time you clean up that bore it will be oversize and it most likely is oversize already from the looks of the polished area, i see this on race motors with extra piston clearances and yours looks stock so your not going to build up enough heat to need that. I could be wrong since were just looking at pics but you likely will have to go next oversize and start over to get a good bore that will last.
Last edited by H2OPERF; 03-26-2020 at 08:26 AM.
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03-26-2020, 08:59 AM #7
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03-26-2020, 09:31 AM #8
Damn andy them cyls are not honed bro,they would chew up a set of rings in minutes.Post #3 is what your looking for. I thought you had all 4 cyls bored and honed ? if you can even feel a finger nail grab on the hone its junk.If all the cyls have no ridge on the top a good hone will clean it up.Those motors are loose from the factory so a couple thou over aint no big deal.Ive seen 3-4-5-6-7 thou undersize factory omc pistons new out of the box and have never had a problem with them.Or your going to need all 4 bored and new pistons.Too bad ya live in Scotland brother I could bore them for ya and get ya some pistons cheap but shipping would be pretty bad.
I may be slow but im ahead of you. *hit's only ankle deep but you went in head first.
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03-26-2020, 01:37 PM #9
Hi Ken was just about to send you a pm bro. The hone job i was ripped off by time. It was ment to be a freshen up and the guy said that was all it needed
Will try and find another shop near me. Will be hard at the present time as we are on lock down for at least 3 weeks.
Is the chip in the nickasel going to be a problem ??
Regarding the pistons i can arrange shipping i had one sent from Canada by DHL it cost £50 but i had to get it. So if you have access to 4 buddy i will take them.
Back to the bad hone would it be OK to use a 3 leg rigid hone, the type that goes on a electric drill or is that just going to make the matter worse ????
It is a tough one. I stay in the middle of no where
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03-26-2020, 02:15 PM #10I may be slow but im ahead of you. *hit's only ankle deep but you went in head first.
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03-26-2020, 02:37 PM #11
No plating on ur cylinders they are cast iron bores , one thing if you have to go next over make sure the guy knows he has to under cut the aluminum at the bottom of the bore... the pistons go past the cast sleeve and if you dotn cut the alumium back it will cause issues
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spybot thanked for this postpowerabout liked this post
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03-26-2020, 04:27 PM #12
Funny how some blocks bore and don't touch the alum to the bottom floor and some do? also it depends on how big ya bore it as we know wiseco makes .064 pistons and ive seen shops not get the bore centered and I will leave an edge on one side of the alum on the bottom floor,it don't take much but when ya put it together and trun it and one piston skirt bottoms out and locks it up that's when wrenches start flying hahaha .
I may be slow but im ahead of you. *hit's only ankle deep but you went in head first.
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03-27-2020, 02:14 AM #13Screaming And Flying!
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03-27-2020, 02:17 AM #14Screaming And Flying!
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03-27-2020, 08:50 AM #15
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