Briggs Pressure Lube Opposed Twin Cleanup

I figured I'd make a new thread for the tear down of my 18hp oppy to keep the MTD thread a little less busy.

Got it part way torn down and removed the valves, rods, and pistons:



Lapped the valves into the seats, they didn't turn out too bad. Then I had to grind the stems a bit to get the clearances within spec.



Picture of my sweet homemade spring compressor in action:



Hahaha.

One thing I found was some real rough looking rod bearing surfaces, which is quite odd:





The crank journals have some streaks but no marks or anything:



Not sure why the rods are like that, almost looks like oil starvation or something. Pretty rough looking, but there aren't any real bad grooves or any missing material, so I'm gonna clean them up with some 800 and 1000 grit. Should be able to smooth em' out again without wrecking the clearances. I'm gonna polish up the crank journals as well.

More updates to come!

Rod bearings do look a little scorched. Not so bad that you couldn't re-send it again it looks like?

The rod bearing surface, how ruff they are, looks old to me. I would suggest to remount the caps, and use the finest grit sandpaper you got without oil first, and rub the bearing surface once or twice. To see if there are any high spots. Don't worry about the low spots because they fill with oil and become level with the rest of the surface that is in good condition. Chances are, there are no high spots because they wore down already on the crank, and would be better off to leave alone. Which explains the crank's rod journal marks. But definitely polish the crank rod journals with the shoe lace trick.

Yeah I was gonna try the shoelace trick with my 1000 grit sandpaper on the crank journals, shouldn't take much as there aren't any actual marks on the crank.

I think the rod bearings will clean up easy enough, I'll see how that goes next week hopefully.

Doesnt look much worse than my 20hp. I took some worn out strip of sand paper... it doesnt really take any material off, but it polishes pretty well... I put that to my 20hp crank.

Some racing mower forum, they talk about opening up the hole in the crank for the oil, and chamfering the opening to let oil in there easier. I believe they also put a hole in the cap aswell.

They said the upper rods would tend to starve for oil in racing applications.

Maybe someday Ill get that 20 back together and see if I wrecked it or not.

Haha, yeah I remember that engine. Don't forget you're supposed to do a horizontal conversion on that one!!

Yeah I've seen a few different oil mods done on these to help the rod bearings, probably works pretty good. This engine should be fine though since it's a pressure lube model. It delivers oil right to the rods through the crank.

Oh right you got one of those fancy units...


Yeah, Ill get around to it sooner or later...

Yessir, getting pretty high tech!

I'll be waiting for that conversion to be finished, haha.

Haven't gotten to the rod bearings yet, been fighting with trying to fix a chainsaw the last little bit  But today I took a minute to pull the bottom cover off and check things out.

Both lower crank bearing surfaces looked great, which is a relief. So then I decided to dissassemble the oil pump and check it all out:









Everything looks pretty good! All the surfaces have a beautiful finish, no galling or pitting or anything. No play in the rotor shaft either.

I don't have the ability to check the rotor clearances nor do I think I could locate the specs, but judging by the lack of wear, I'n thinking it should be okay.

Gonna flush everything out of the oiling system real good before reassembly, so it should be like new when it's all put back together!

Okay, so I finally took the time today to clean up the rod bearing surfaces.



As you can see, they turned out pretty nice!





Despite the low spots, they have a real nice finish! Perfect smooth feel with no catches or anything.

I feel pretty confident that I can run these without any issues.

Looks like they cleaned up nice. How do the rings look? They need replaced or look good?

Well they could probably stand to be replaced really, but I'll probably just run them. I've had pretty good luck re-using piston rings, even though it's kind of a no-no, haha.

Rod bearing surfaces look real good. Those scratches will fill with oil and be level, no worries. Re-using rings a no no, first time I heard that one. Take a file to them on every surface knocking down any high spots, then chamfer all the edges so they don't dig into the cylinder walls or pistons. End gap usually won't matter to much as long as the phasing is done right. I usually phase mine 180 from each other, instead of the 120 degree. To give the escaping gasses the hardest time and the longest time to get into the crank case. I then pack the compression ring grooves on the pistons with lithium grease so it burns and makes carbon faster behind the rings for better and quicker sealing of the rings. Yes, it will smoke like a freight train on first startup but goes away after a while when it warms up good. All that carbon you scrape out on the piston behind the rings does have a purpose being there of helping to seal the piston rings because the rings themselves in not a perfect seal to begin with.

Thanks prancstaman. Yeah I always stagger the compression rings 180 apart as well, had pretty good luck with it.

I actually cleaned up the outside of the pistons real well with a brass brush, some 1000 grit, and some brake clean earlier today. They turned out quite nice and I was able to get rid of a couple marks that were on them. Once I pick up some more intake cleaner I'll de-carbon the piston crowns and they should pretty much be done.

Okay we got pretty much a bare block now:



Gave both cylinders a good honing, and they didn't turn out too bad.



Then I got around to the final part of cleaning the pistons, which was just cleaning the carbon off the crowns:



They came out real nice!



They should be good now. I tried the rods on the crankshaft as well, and they seem to fit well. No excessive clearnaces and they have that nice swing on the crank. I think they'll work good.

After that was a block cleanup:



She's nice and clean now! Flushed out all the oil passages as well.

Then the last thing I did was re-install the crank and cam and get the timing set:



Had to deal with two broken bolts before I could go any further. Got one out today, but the other one is still being a bugger so I'll have to keep at it for a bit.

After that we can continue re-assembly!

Ah yeah, I see the bolt. In the exhaust right?

Yeah that's the one I got out today, it wasn't too bad of a job luckily.

Busted bolts are a pain. The just get in the way at the worst times. I just got a Peerless 820 with a busted off bolt for the brakes... Gonna try the double nut trick.

Looking good!

Busted bolts can be depressing. I had on in my 14hp OHV Tec head. Ended up drilling it out, then tapping the hole for a size bigger bolt.

Ive had really good luck with welding nuts to whats left of the bolt, I think its the crazy heat from the welder that does it. sometimes it takes 1 try sometimes it takes 10 but i havent had it fail yet. have had to just keep tacking on the remained of the bolt to get it above grade so that I can weld a nut to it. worked great on my 5.3 chevy heads

Yeah I've done that trick before and you're right it definitely works good. I have it part way drilled out right now though, so if heat and an easy-out won't do it I'll probably have to drill and tap for the next size. Oh well, can't win 'em all. Haha.

I've got a bead on some opposed engines that I'm supposed to pick up this weekend, one is supposed to be a pressure lube too. I see in your pics that the oil pump actually looks pretty beefy on these. The only oil pumps I have seen on mower engines before is the tecumseh ones that use a plastic housing with a metal plunger in it. This setup looks a lot better.

If you ever want to check your rod clearances, go to an auto parts store and ask for a plastigage. It's a strip of hard plastic kinda stuff that comes in a paper. You put a piece of it across the bearing and snug the bolts up, then you measure how wide the plastic is with the marks on the paper package. They come in different size ranges. I think they recommend .003 clearance for splash lube engines. I would think you'll be fine though with the oil pump. Looks like they cleaned up good.

On the one I built for the gtr 4 zero, I actually took the rings off to clean rust off of them and then put them back on. I was working on a pretty extreme budget... But it worked out, didn't break any that I know of.

Ooo, you'll have to post some pictures of that oppy haul once you get it!

I was thinking about picking up some plastigauge to check the rods, being that I don't have a micrometer. I could still do it now really. I'd actually rather do it when everything was in the block, just so it's sitting in it's spot. Also yeah the rotor oil pump is a pretty neat setup. Real cool to see how the whole system works.

Well I've finally been making some headway on the reassembly of this engine lately:



Got the pistons/rods and the flywheel installed and all torqued up.



The base was just stuck in place in that picture, but tonight I actually got it bolted on and sealed up. Got a new lower crank seal for it too:



New crank seal put in and and oil pump reassembled:



Not too bad! Man it'll be nice to finally have it running again, haha. Getting the head gaskets somtime this week, and after that I should need any more parts.