Author Topic: 18 hp oppy fresh rebuild issue  (Read 8941 times)

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Offline SINNER67

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18 hp oppy fresh rebuild issue
« on: December 06, 2015, 09:35:20 pm »
Hello all.  First post,  but I've been turning to you for reading material for a while now.
So tonight I buttoned up my motor and tried to start it and the starter won't turn it. It's even hard turning with a breaker bar on the flywheel nut.

The motor is a briggs 18 hp opposed twin 422707

Here's the story. ..
I decided to tear the motor apart after mowing the lawn for fifteen minutes then it dies.  I noticed oil leaking from the lower cylinder head bolts, and lead me to think blown head gasket mixed with rings letting to much oil past the piston.

So I took the motor out of the mower.  Pulled the heads off.  Took the crankcase cover off. Pulled the pistons, declared the cylinder walls.  New rings, filed valve ends to proper clearance,  put all back together and noticed it's got a lot more rotating resistance even with the heads still off.

It seems like the extra resistance happened when I put the rod caps on, while rotating the crank slightly to torque the cap bolts it was difficult (from new rings on cross hatch cylinder).
Then when the caps were torqued to 180 in. lb. it got a little more resistance.  I put black all purpose grease on the rod crank journals as assembly lube.

I'm sure I left something out for diagnosticing.

Does this sound fairly normal for the added rotating resistance,  or did I screw the pooch somehow?  :bash: :bash:






Offline redline

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Re: 18 hp oppy fresh rebuild issue
« Reply #1 on: December 07, 2015, 07:37:46 am »
Did you mark the caps so they went back on the same rod?
Ed King

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Offline SINNER67

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Re: 18 hp oppy fresh rebuild issue
« Reply #2 on: December 07, 2015, 08:39:08 am »
I did not mark them. But I did take one out at a time and  put the bolts and cap back on the rod.
There could be a chance that I flipped a cap 180°, if it's possible. 

I also used plastigauge and got .0015" but it was like 35 degrees in my garage when I did.

I don't know what stock specs are on the clearance of the rod bearing.  I did read that rooster likes .003"-.005" on a race prepped  oppy

Offline PJG56

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Re: 18 hp oppy fresh rebuild issue
« Reply #3 on: December 07, 2015, 05:50:57 pm »
Rod caps most likely backwards
Paul Guptill  (oppy) #238modX
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Offline SINNER67

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Re: 18 hp oppy fresh rebuild issue
« Reply #4 on: December 07, 2015, 11:28:52 pm »
Ok. So I can leave the heads on and just take the crankcase  cover off.

Now is there a good way too tell if the caps are backward?
Maybe some cast marks that are supposed to line up,  or do I need to aquire a bore gauge doodads, and spin it in the journal to check round versus oval?
Or any other suggestions

Thank you all for the replies.  I'm glad the grass isn't growing anymore this year. 


Offline chavez

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Re: 18 hp oppy fresh rebuild issue
« Reply #5 on: December 08, 2015, 12:38:17 am »
Honestly, your best results are going to include getting your rods/pistons and crank out on the bench so you can take some measurements.  If you don't have the tools, ask around or find a machine shop if they'll do it for you.  You need to have either id snap gauges, or id bore mic to measure the bore of your rods.  Od mic to measure each journal of your crank throws, not only for od, but for out-of-round.   While you are at it might not hurt to check if your crank is bent.  Your posting seems to indicate this may be beyond your experience, so I'd suggest someone that's familiar with these tools and checks to do them for you and explain along the way.
Travis Callaway

Offline westcoast racer

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Re: 18 hp oppy fresh rebuild issue
« Reply #6 on: December 10, 2015, 05:31:29 pm »
Did you check the ring cap before putting them on the pistons?  Did you put the pistons back in the same location with the rod facing the right direction?
Dan Borba

Offline SINNER67

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Re: 18 hp oppy fresh rebuild issue
« Reply #7 on: December 10, 2015, 11:06:39 pm »
I did check the ring gap on one ring for one piston. I had a touch of impatient  laziness. The ring gap was .011... but I should have checked all four compression  rings.  I did put the pistons in the correct cylinder and did not turn them upside down.  The pistons have an arrow indent that points up.  And I labeled upper and lower. 

I have not gotten into the motor again to check the rod caps yet.  I'm hoping this weekend I will have time.

I wonder if the friction of the new rings against a fresh cross hatch is what I have.  I only put 30 weight on the rings and cylinder for reassembly, and I knew it wouldn't stick around too long.

I might have turned a cap around. Mixed with new rings,  and worn starter.

If I pull the heads will I need new head gaskets?  Or will they reseat again

Offline Jim Knutson

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Re: 18 hp oppy fresh rebuild issue
« Reply #8 on: December 11, 2015, 12:04:44 am »
If they are the old metal clad gaskets, they will reseal if in good shape.....graphoil gaskets are garbage before you even use them, and wont reseal!....lol.
If you quit when you're behind, you will never win.

Offline PJG56

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Re: 18 hp oppy fresh rebuild issue
« Reply #9 on: December 11, 2015, 06:27:29 am »
If head gaskets tear a little,put a little atv sealer on head gaskets and reuse
Paul Guptill  (oppy) #238modX
2012 slmra mowstock champion(builder/owner)

2013 slmra mowdified champion(builder/owner)
2013 ARMA national champion Mod-X(builder/owner)
2014 ARMA national champion Mod-X(builder/owner)
2014 All American Champion Mod-X/CP(builder/owner)
2014All American Champion FXT (engine builder)
2014 All American 2nd place SP(builder/owner)
2015 All American 2nd place BP (builder/owner)
2016 OutlawTriple Crown FXT Champion (engine builder)

Offline SINNER67

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Re: 18 hp oppy fresh rebuild issue
« Reply #10 on: December 13, 2015, 01:01:25 pm »
Ohhhh k. I made time for the old crapsman yesterday and this morning.

I definitely had the rod caps on backward.  I flipped them and noticed a small scribe mark that I put there when I took it all apart.

I advise that when you put a motor back totogether, you should leave beer out of the equation... :uhh:

So I got the motor back in, left all the belts and such off for now. Starter is junk, I pulled it apart and put some grease on the top bushing.  It should better,  but still shot.

So I wrapped a rope around the lower pulley and gave it all I had. The motor spun nice,  I got maybe a revolution and a half. No spark... pulled  spark plugs and grounded one, turned the starter over,  motor spun nice with no compression and produced a very faint weak spark.
I then pulled the top shroud and check the coil gap with business card, and sanded it all shiny.   Then checked spark again, still weak.

So next on the list is a starter and coil. Grr   :mad:

Offline BIG AL 202

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Re: 18 hp oppy fresh rebuild issue
« Reply #11 on: December 14, 2015, 08:59:16 am »
NO BEER, CLEAN AREA, AND I LIKE TO BUILD BY MYSELF SO I DON'T FORGET AND NO DISTRACTIONS! 
ALWAYS VOTE FOR ED!   FONGS BROTHER FROM ANOTHER MOTHER!

Offline rotten ron

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Re: 18 hp oppy fresh rebuild issue
« Reply #12 on: December 25, 2015, 06:16:05 pm »
You should be able to drink beer and work on an engine,I did it for years but not now,I haven't done that for 15 years,more beer for others

Offline BIG AL 202

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Re: 18 hp oppy fresh rebuild issue
« Reply #13 on: December 26, 2015, 09:55:08 am »
You should be able to drink beer and work on an engine,I did it for years but not now,I haven't done that for 15 years,more beer for others
MORE BEER FOR BERT!
ALWAYS VOTE FOR ED!   FONGS BROTHER FROM ANOTHER MOTHER!

Offline SINNER67

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Re: 18 hp oppy fresh rebuild issue
« Reply #14 on: December 28, 2015, 08:23:24 pm »
Oh yeah. .. I thought the beer wouldn't be an issue.  But it seems to erase parts of my memory.

Anyways.  I threw a new coil and starter in it,  and she fired right up.  Smoked like crazy for a while,  then didn't smoke at all. Shut er down and changed the oil.
I ran it for about twenty minutes. Made me a happy camper