Predator 420 Hard To Pull, Sputtering

[SquidBonez]

I just built a stage 1+ (stage 1 kit but with billet parts, stock cam) Predator 420 hemi and I can't get it to start in order to break it in. The pull cord jerks back in my hand and damn near rips my arm off occasionally. It will sometimes sputter and spit puffs of smoke out of the exhaust and also backfired out of the carb once. Made sure I was getting spark and adjusted my valve lash correctly. Coil is gapped correctly. However, this is only an issue when the spark plug is in; motor turns over just fine without it. Makes me think it's a compression issue. I thought it was just the fault of the 50lb springs originally but no. Any ideas?

 

[SquidBonez]

Checked the cam alignment. As you can see they are aligned (since the gears are helical it looks slightly misaligned but they aren't). Should also mention I have a timing advance key, but I installed it correctly. Might go back to the stock key to see if it makes a difference.

 

[madprofessor]

Go to the search bar and type in "How much pullrope are you using?" It's down at the bottom of the page that comes up.
Pay special attention to where I had been doing 3' pulls, and that's where it always snatched back, at the end of the pull. I was using 36" of a 51" rope. The snatchback is the plug firing the mixture in advance of the piston reaching TDC, but the rope pull isn't long enough to keep it from stopping short of TDC. Hence the explosion turns the motor backwards.

 

[SquidBonez]

Go to the search bar and type in "How much pullrope are you using?" It's down at the bottom of the page that comes up.
Pay special attention to where I had been doing 3' pulls, and that's where it always snatched back, at the end of the pull. I was using 36" of a 51" rope. The snatchback is the plug firing the mixture in advance of the piston reaching TDC, but the rope pull isn't long enough to keep it from stopping short of TDC. Hence the explosion turns the motor backwards.

So retarding the timing and/or going back to the stock key might fix this problem then? Sad part is I have no idea where my stock key went. Gotta wait on a new one...

 

[madprofessor]

Nope, timing is always advanced, has to be to run right. My current kart got a billet racing flywheel that comes at 28 degrees advance, and I'm running a #6 (7.2 degrees) advance key to boot for a total 35.2 degrees advance.
The point of the pullrope thread was to explain the importance of having a long enough pull, to have the motor spinning fast enough and continuing it's revolutions long enough so that it isn't almost stopped when the pug fires. Without that follow-through of the pullrope, the explosion when the plug fires will push the piston backward if that's the easiest direction for it to go.
If you force the motor to spin the right direction to well past TDC via a longer pull on the rope, then the explosion will continue to push the piston in the right direction. It's the stopping of the pull right at the point the plug fires that makes it run backward, snatching your fingers out of joint. Measure how much rope comes out when you pull, then pull it all the way out and measure how much more there is for you to pull if you just take a step back for a longer pull.
Read the entire pullrope thread.

 

[Denny]

Make sure the decompression stuff is still intact and moving freely on the cam. Make sure valve lash is set right. Rotate engine to compression stroke. Slide rope back into recoil all the way. Pull slowly, engaging the pawls. Once done pull sharply with all your might.

 

[SquidBonez]

Make sure the decompression stuff is still intact and moving freely on the cam. Make sure valve lash is set right. Rotate engine to compression stroke. Slide rope back into recoil all the way. Pull slowly, engaging the pawls. Once done pull sharply with all your might.

Cam is brand new, decompression works just fine

 

[SquidBonez]

Nope, timing is always advanced, has to be to run right. My current kart got a billet racing flywheel that comes at 28 degrees advance, and I'm running a #6 (7.2 degrees) advance key to boot for a total 35.2 degrees advance.
The point of the pullrope thread was to explain the importance of having a long enough pull, to have the motor spinning fast enough and continuing it's revolutions long enough so that it isn't almost stopped when the pug fires. Without that follow-through of the pullrope, the explosion when the plug fires will push the piston backward if that's the easiest direction for it to go.
If you force the motor to spin the right direction to well past TDC via a longer pull on the rope, then the explosion will continue to push the piston in the right direction. It's the stopping of the pull right at the point the plug fires that makes it run backward, snatching your fingers out of joint. Measure how much rope comes out when you pull, then pull it all the way out and measure how much more there is for you to pull if you just take a step back for a longer pull.
Read the entire pullrope thread.

I know the timing is always advanced, I'm just wondering if it would help to go back to the stock key (which would lessen/retard the timing). Also re-checked my valve lash, set it to 0.002" on the compression stroke. Will report back with results.

 

[madprofessor]

At one point I had a #9 (10.8 degrees) advance key on my 28 degree flywheel, was a reading it upside-down thing that they sent it to me thinking it was a #6 key. For some testing I took it back out and put the stock no-extra-advance OEM key back in, and it didn't make one little iota of difference in the testing being done.

 

[SquidBonez]

UPDATE: got the engine running

All I did was go back to the stock key and reset my lash (on the compression stroke) to 0.002. Still sorta difficult to pull start but it runs now. Let it run for 20 or so minutes and then opened it up to check for any clearance issues. All good inside. Only thing of note was that the plug was completely black when I checked it (keep in mind this was a brand new plug). A richer pilot/low speed jet came with my stage 1 kit so I'm just going to go back to the stock jet. Picture below:

My only question right now regaurds how the engine sounds. Sounds kinda clacky to me. I hope it's not rod knock. Brand new connecting rod/bearings but does it sound alright to you guys? Keep in mind it's sitting on a workbench so it could be something else clacking. I also made sure to double check the rod bearings and re-torque the rod bolts. They seemed fine as did the crank.

 

[madprofessor]

Sound of engine at that distance and position has exhaust covering up any internal sound, try recording it from beside the engine. What it does sound like as recorded sounds pretty natural.
You say brand new cam and such, and needs a break-in. What are you using for oil? Nawt fer nuttin', but I'm a die-hard believer in "Royal Purple Break-in Oil" from my local auto parts house (I like O'Reilly's). They don't even stock it in the store, order it for me every time, about $11 per qt., and I keep using it for any oil change.

 

[SquidBonez]

Sound of engine at that distance and position has exhaust covering up any internal sound, try recording it from beside the engine. What it does sound like as recorded sounds pretty natural.
You say brand new cam and such, and needs a break-in. What are you using for oil? Nawt fer nuttin', but I'm a die-hard believer in "Royal Purple Break-in Oil" from my local auto parts house (I like O'Reilly's). They don't even stock it in the store, order it for me every time, about $11 per qt., and I keep using it for any oil change.

I've been using 1 quart of Royal Purple 10w30 synthetic. As for the noise I can record another video once I run it again. I might just be getting paranoid. Building the engine is always the most nerve-racking part of a build for me.

I noticed a bit of "play" at both TDC and BDC. Not like side to side play, but when I spun the motor over I would feel a sudden lack of resistance at TDC/BDC. That's why I checked the rod bearings and crank (both looked fine, bearings are seated properly). That's what got me paranoid. Might be worth ordering some new bearings just to be safe.

 

[madprofessor]

I noticed a bit of "play" at both TDC and BDC.

You're even worrying me now too. Never heard of anybody trying to run a motor with the rod bearings loose on the crank journal. Please explain a different way what you mean by play at both ends of the rod travel. I get it that the rod can't slip side to side. That only leaves.......................
(1): a rod bearings' I.D. being larger than the crank journal's O.D., or................
(2): the piston's wrist pin journals' I.D. being larger than the wrist pin's O.D.,....................

 

[SquidBonez]

You're even worrying me now too. Never heard of anybody trying to run a motor with the rod bearings loose on the crank journal. Please explain a different way what you mean by play at both ends of the rod travel. I get it that the rod can't slip side to side. That only leaves.......................
(1): a rod bearings' I.D. being larger than the crank journal's O.D., or................
(2): the piston's wrist pin journals' I.D. being larger than the wrist pin's O.D.,....................

Yeah since I made that last post I've determined I was getting a bit of rod knock. I knew something was up, just hard to hear it in the video. Luckily I only ran the engine for 20 minutes and didn't go over idle. Checked the crank for damage and it is undamaged. The bearings look a little marked up; I'm thinking some metal shavings might have gotten in there from when I clearanced the engine block. Even after torquing the rod bolts a bit over what they call for I still get this slight amount of play. Side to side play is one thing, but at TDC I get a tiny amount of up and down play. Still unacceptable despite being small. I don't think it's the piston because I pulled the piston to install the rod and it had no play on the wristpin. I have new rod bearings on the way and won't run the engine until I install them. Could this have been part of the reason why my engine was hard to pull over?

 

[Denny]

Did you plastigauge the bearings and crank to check the clearances?

 

[SquidBonez]

Did you plastigauge the bearings and crank to check the clearances?

Oh crap I forgot to get plastigauge. What do I do if the plastigauge shows I have too much clearance? What's even the fix for that besides new bearings? As you can tell I'm still learning how to build engines.

 

[madprofessor]

Every auto parts store will sell you a plastigauge, just be sure to get the one that has the range of width markings on it you need.
Only extreme slop of the crank journal could cause you to get a into binding situation, the only reason it would be harder to roll over.
Harbor Freight techs can't even come up with a part number for the item #39 Crankshaft Assy. for the hemi or non-hemi 420, and BMI only lists a crankshaft for Honda GX390 and Clone for $56.
If you need a new crank, best of luck to you on getting a correct match. I'm unsure of how well Predator parts cross to clones.

 

[SquidBonez]

Every auto parts store will sell you a plastigauge, just be sure to get the one that has the range of width markings on it you need.
Only extreme slop of the crank journal could cause you to get a into binding situation, the only reason it would be harder to roll over.
Harbor Freight techs can't even come up with a part number for the item #39 Crankshaft Assy. for the hemi or non-hemi 420, and BMI only lists a crankshaft for Honda GX390 and Clone for $56.
If you need a new crank, best of luck to you on getting a correct match. I'm unsure of how well Predator parts cross to clones.

I don't think I'm going to be needing a new crank. Although if I did I've seen them for sale online.

 

[SquidBonez]

Update: So glad I checked the bearings. They're shot. When I pulled the rod cap off there was literally an aluminum shaving sitting on the crank. Crank is undamaged and clean. Rod itself is fine. The bearings meanwhile...


I think residual metal shavings from clearancing the block combined with turning the motor with no oil while checking said clearance caused it. New bearings are on the way.

 

[madprofessor]

I can't see how those bearings would have had you feeling slop at TDC or BDC, but OH, DUDE!!!!! Go buy a lottery ticket right away, because your lucky star shined on you that the crank journal's undamaged. Those poor bearings are scarred up worse than my bod or my psyche!