1988 Scag w/ Kaw FC420v-BS02 and slight knock but runs great!

Okay, so I have finished my 1988 Scag mower restore...

Before...




After...






now, I finally got a chance to tear into the engine to find out what that knock is. With some research I'm almost wondering if its the counterbalance making the noise. It's not terribly loud and it seems common for the counterbalance bearings/ bushings to wear to the point of allowing it to make noise.

Is there a way to check the counterbalance for wear? WITHOUT Tearing it apart and mic-ing clearances?

Okay, so I tore the engine apart and have MICed everything that I could that could be the issue of the knocking.

Piston Pin Hole is over on specs with visible signs of wear and the connecting rod large bore is as well. Everything else is within specs per the manual.

Now, I a;ready found a new Piston and have that on the way and I'm looking for a new connecting rod #13251-2063..

Anyone have any leads for one shipped for <$60???

Also, is there a cross reference list for the connecting rod to see if other rods will fit correctly to open up the range of potentially available rods?

Thanks.

Mastiffman said:

Good day fellas!

I have a Kaw FC420V that needs a rod which I'm getting ready to replace and I'm curious if I can use a Rod from any FC420V or does it have match the last 4 revision(?) letters of the model. In this case BS02.

I can't seem to find any used ones on the bay. I would rather not drop a full $65+ on a new Rod if not a full rebuild of the engine. Just going to replace the Rod if the crank journal is fine as well as de-carbon it and do a valve and gov/carb adjust (Surges at idle).

Thanks in advance.

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Hi! I would question your diagnosis. If you have an engine that has had a slight knock for several years and it was a rod knock, it wouldn't have made it this far. By chance, do you run Regular unleaded fuel? That engine design along with low grade fuel will create an excessive amount of carbon build-up in the cylinder head and ultimately it sounds like the rod is ready to go, but in reality, the cylinder head just needs to be de-carboned and replace the gaskets.
I would look at that before I would pull the engine for a complete teardown that it may not even need. If I am correct, start buying better grade fuel.

Good Luck!

Thanks for the reply.

Too late! lol

I am familiar with carbon deposit build up and yes for a 1988 engine, this one wasn't too bad inside compared to some of the Onan's that I've dealt with in the past.

I did tear everything down to the block, puled the crank and all. I had to know what was out of spec and what wasn't. I found that everything that could be making a knock (Counterbalance and connecting rods, piston, wrist pin, connecting rod and crank) was well within proper operating spec and nothing right on the verge of needing to be replaced. The cranks piston pin (Rod journal) was completly round as well. EXCEPT, the large bore of the connecting rod... It is supposed to no more than 1.6169" and was 1.6175" running the length of the right (top to bottom) and was 1.6155" 1.6160" side to side. So that bore was oval shaped. A tell tale sign of Rod Knock... And out of spec.

The small bore was right on the cusp of needing to be replaced @ .8685"-.8690" The piston pin was in great shape and perfectly round the length of it @ .8665". BUT the pistons wrist pin holes were over the Max .8676" @ .8690"-8.695"...

So between the large bore on the Con-Rod and the Horrible piston pin holes, that's where the knock was coming from. I have a new piston and rod coming and will most likely hone the cylinder and put new rings in as well.

Okay,

SO I have the new parts ready to go. Piston, Rod and Rings.

I'm going to be honing the cylinder today and hopefully start reassembly.

Any Tips?

Mastiffman said:

Okay,

SO I have the new parts ready to go. Piston, Rod and Rings.

I'm going to be honing the cylinder today and hopefully start reassembly.

Any Tips?

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I have to hand it to you, you have done an awesome job restoring this unit. It looks magnificent! Engine wise, I wish I had more techs that would take the time to spec out the components like you did. That is the right way. I am still blown-away that the rod was oval for that long and didn't fail. That's one for the record book.
I think you are more than capable of rebuilding this engine to better than new. Not sure what tips I could give unless you're never honed a bore before, but I have a feeling you're pretty experienced. Do you have access to the torque specs? If there is anything I could assist you with, let me know. I have full access to the service manuals, etc.

I hope you plan on posting picks of the completed unit. I know my friends at Scag would be impressed as well.

Thanks a Ton for the compliment and encouragement. That means a lot to me.

I put a lot of hours into this restore and I'm just about done... This was my first honing believe it or not. So I have one under my belt now. Won't be the last. I do a lot of reading, watching videos and looking at repair manuals, becoming familiar with the parts and seeing just how available potential replacement parts are before any disassembly. I have rebuilt an old 1970 Onan Generator engine. So this didn't seem to hard. Just a bit different in design. There was no way that I wasn't going to MIC everything that I could to find that knock. This is the first of a few noises within my small fleet of machines that I'm going to be taking care of.

I Got the engine back together late last night with a small bottle of assembly lube, some rags, parts cleaner and some 9mil gloves. I set a goal of honing and getting it rebuilt for the day and didn't want to go to bed until I did everything that I could. Today I've sprayed my last two parts. The PTO pulley's underneath. I had to weld a crack in the bottom of the exhaust manifild that was spitting carbon on the old paint finish so that was a must to fix. Got that fix and mounted the engine on the engine deck. Finished with the initial throttle, choke and carb settings. I need to fix a couple of raw rubs in the wiring harness, get a few 2.5" mounting bolts for the new (used) oil filter bracket an oil filter, oil, lube everything up an the last touch I'm going to pickup today... DECALS...

I couldn't find the pull starter decal anywhere so I carefully removed the three decals and ID tag from the cowl and designed my own decals for the top of the cowl and pull starter on my computer software and I go to pick those up in a few! Hoping to get it started before the night is over.

More Pics...



















More to come later...

P.S. I also have tear down and repair pics if anyone would like to see how bad the deck really was... Put it this way, The only reason I spent half of the build time with repairing it was because I couldn't find an other one. But she's solid as a rock now. New bearings and bushings and all. I took the spindle completely apart as well a the drive wheels and their pulley's and the levers that move them. It's all tight again like new. It's going to be hard to sell this thing, if I can bring myself to do it.

Okay,

So I'm fully stumped. I literally mic'd everything that I could initially and second and third time now. This engine has a new piston head, rings, con-rod, counterbalance link rods and everything else literally MIC's well within allowed tolerances...

Initially I honed the cylinder, put new piston, con-rod and rings together with the old wrist pin as it was perfectly round the length of it and within spec. I added an oil filter adapter which I initially blew out with carb cleaner and compressed air and used Fram PH4967 as that's what I found for a cross reference online to the original Kawasaki filter. It was recommended by a local small engine rebuilder that I use Valv. F1 high zinc 20w/50 for all small air cooled engines. Put it back together and there was still a knock noise. Pulled it apart and realized that I MIC'd the small bore of the Link Rods wrong and they were actually over by .002". So I replaced those thinking that would be the end all issue.

Back together with the same oil and filter. Runs great BUT Knocking starts about 30 seconds into running STILL. Sounds like a Rod Knock!? I pulled the entire engine apart minus pulling the piston, again this morning and MIC'd the crank journal and connecting rod large bore after torqued and I'm no more than .001" clearance between rod and crank. Checked the bearing per manual recommendations, the cam journals and bearings and the weight pin hole and pin as well as blew out the oil passages on the crank and checked to make sure the Rod Oil passage was clear. All is Good...

I purchased an oil pressure gauge from O'reilly's and I'm getting 45+ PSI at the top access hole of the filter adapter.

Where the heck is/could this knock coming from? I didn't check the axial measurement as I didn't change anything related to it.

Could it be a combo of the oil filter and high Zinc 20w/50???

I'm stumped... I thought about taking the oil filter adapter completely off and running the 20w/50 in there or straight 30w and see what that does. But when I disassembled the engine the rod journal was dripping with oil.

Mastiffman said:

Okay,

So I'm fully stumped. I literally mic'd everything that I could initially and second and third time now. This engine has a new piston head, rings, con-rod, counterbalance link rods and everything else literally MIC's well within allowed tolerances...

Initially I honed the cylinder, put new piston, con-rod and rings together with the old wrist pin as it was perfectly round the length of it and within spec. I added an oil filter adapter which I initially blew out with carb cleaner and compressed air and used Fram PH4967 as that's what I found for a cross reference online to the original Kawasaki filter. It was recommended by a local small engine rebuilder that I use Valv. F1 high zinc 20w/50 for all small air cooled engines. Put it back together and there was still a knock noise. Pulled it apart and realized that I MIC'd the small bore of the Link Rods wrong and they were actually over by .002". So I replaced those thinking that would be the end all issue.

Back together with the same oil and filter. Runs great BUT Knocking starts about 30 seconds into running STILL. Sounds like a Rod Knock!? I pulled the entire engine apart minus pulling the piston, again this morning and MIC'd the crank journal and connecting rod large bore after torqued and I'm no more than .001" clearance between rod and crank. Checked the bearing per manual recommendations, the cam journals and bearings and the weight pin hole and pin as well as blew out the oil passages on the crank and checked to make sure the Rod Oil passage was clear. All is Good...

I purchased an oil pressure gauge from O'reilly's and I'm getting 45+ PSI at the top access hole of the filter adapter.

Where the heck is/could this knock coming from? I didn't check the axial measurement as I didn't change anything related to it.

Could it be a combo of the oil filter and high Zinc 20w/50???

I'm stumped... I thought about taking the oil filter adapter completely off and running the 20w/50 in there or straight 30w and see what that does. But when I disassembled the engine the rod journal was dripping with oil.

Click to expand...

I know you have more patience than me. Are you running the engine with the pulley and clutch installed?

Honda Tech said:

I know you have more patience than me. Are you running the engine with the pulley and clutch installed?

Click to expand...

Ha ha. Thanks. My wife calls me "obsessed"! lol

No pulley yet. I wanted to make sure that it was running well before fully hooking it up. It's definitely inside the engine.