slipping timing issue

W

W5R

New member
I have an open animal that I ran all last season without a single issue, but after making some changes over the winter, I having an issue I simply cannot fix no matter what and would like some opinions here. This is a stroker animal, flathead crank, 2.776 bore Havoc dome piston, somewhere around 12.5 compression if my math is right. When I first got the engine back together after the rebuild, first night out with it the flywheel slipped time because I had forgot to lap it to the crank when I set the timing. Ever since it slipped that first time, I have not been able to get this flywheel to hold time at all. Sometimes it will run 30 laps or more before it slips, and sometimes it will slip as soon as you start it up, let it run a few minutes and shut it off. I have lapped it to the crank for over an hour several times, being sure to clean the lapping compound off the crank very well and completely, both with just brake parts cleaner, and with soapy water and brake parts cleaner both, nothing seems to make it hold time.

Now, after lapping it this last time I noticed that I have lapped it so much that the back of the flywheel is actually rubbing against the block support behind my flywheel, which Is the fastermotors block support...so apparently I have literally worn the flywheel taper out from lapping it so much and simply can't lap it anymore, the flywheel is now junk, basically. What id like to know, is it possible that all that lapping has also worn the crank taper down too much as well, and I will now need to put a new crank in the engine along with the new flywheel? I'd also like to know, is it possible to have the compression high enough on these engines that it gets to the point where the compression is causing the flywheel to keep slipping time when the engine is shut off or when I let off the throttle at high rpm? I have never heard of compression affecting the flywheels ability to hold time, but what has me wondering that is because the only changes I have made to this engine since last season have been the bigger bore with the dome piston, and the change in timing, since I took a couple degree's timing out of the engine after adding that much compression. The dome on the piston is milled to .070" instead of the .125" it came at new, using a .050" copper head gasket, with no contact between the piston and the head or piston and the valves at all, I have enough clearance even at 9000+ rpm. Engine is an absolute beast when it holds time without slipping, but it is costing me money and races everytime it slips, and Is getting annoying. I'm at my wits end as far as what is causing this thing to keep slipping time like this, and really need to figure out what is causing it and get it sorted out. I just don't want to put a new flywheel on it and that flywheel start slipping also and possibly ruin another flywheel, or my crank.

If anyone has any Ideas what can be causing this issue please let me know, don't be afraid to throw some ideas out there if you think you might know the cause, or have had this issue before and worked it out! Got a huge open race in less than a month and I have got to get this figured out....
 
If you are running a key, check the height of the key and make sure it is not higher than the keyway slot. If you are not running a key, measure the large diameter of the taper (where it is contacting the flywheel) and make sure it has not wallowed out the flywheel when it came loose. If this has happened, you are better off just getting a new flywheel with a new straight taper. As far as the compression issue, yes the higher the compression, the more difficult it is to turn over at the start. Sometimes the engine will 'sneeze' while trying to start it and this is the time it usually slips the flywheel. The only solution for that is to reduce the spark lead or use a 'kill' switch to allow the engine to be spun at a higher RPM before you allow the ignition to fire. Anyway, just a couple of things that have burnt us in the past. Good luck.......
 
I would be looking to see if you have a hairline crack in the flywheel. Dye penetrant inspection will reveal cracks that are invisible to the human eye. Any good machine shop has the proper chemicals to accomplish the testing. Typical cracks will develop where 90 degree machining has been accomplished (like the key area on the flywheel). This could happen even though you are not using a key in the slot.

Years ago, we had a rear hub fail (cracked completely around the hub, and the wheel/tire and 1/2 the hub went flying). We took every one of our other hubs from this manufacturer and had them tested. Lo and behold, every one had developed cracks to different degrees. The manufacturer (who sponsored my grandson) changed his manufacturing process to remove the 90 degree hub problem by going to a radius cut instead.
 
01ron said:
I would be looking to see if you have a hairline crack in the flywheel. Dye penetrant inspection will reveal cracks that are invisible to the human eye. Any good machine shop has the proper chemicals to accomplish the testing. Typical cracks will develop where 90 degree machining has been accomplished (like the key area on the flywheel). This could happen even though you are not using a key in the slot.
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Wish I had thought of that, a very good point.

The trouble, the expense, the lost lap times, is it worth it?
 
If the crank was damaged from the lapping, you should be able to see/feel the difference between the lapped area and the original crank journal. If it was damaged, you could probably feel it with your fingernail or any straight edge.
 
Try the ring test. Suspend the flywheel by a string and tap it with a wrench. If it makes a dull thud noise be very suspicious. If it rings like a bell that's s good sign. Compare with another good / new part. A Talcum powder test is also a good indicator of a crack.
Neither of these are fool proof tests but have worked very well for me and others for a very long time.
 
On another post, he started he was using a Briggs PVL flywheel. Not sure if this is the same engine but it looks to be from his description. And no key since he is using a flathead crank with an animal engine/ignition. Keyways are not in the correct place for this configuration.
 
tecbigdog said:
If you are running a key, check the height of the key and make sure it is not higher than the keyway slot. If you are not running a key, measure the large diameter of the taper (where it is contacting the flywheel) and make sure it has not wallowed out the flywheel when it came loose. If this has happened, you are better off just getting a new flywheel with a new straight taper. As far as the compression issue, yes the higher the compression, the more difficult it is to turn over at the start. Sometimes the engine will 'sneeze' while trying to start it and this is the time it usually slips the flywheel. The only solution for that is to reduce the spark lead or use a 'kill' switch to allow the engine to be spun at a higher RPM before you allow the ignition to fire. Anyway, just a couple of things that have burnt us in the past. Good luck.......
Click to expand...

Keyways in the flathead crank and animal flywheel are nowhere close to lining up so they cannot be used, have to lap the flywheel to set timing.

Have checked and double checked the flywheel for hairline cracks with dye, no cracks anywhere but the taper itself does look a little rough on the back side closest to the block. I have a new flywheel that I picked up today, am going to try the new one and hopefully that fixes the issue. I have never seen a stew hub flywheel wear out before, that is a new one for me guys. This is a Briggs pvl flywheel, raptor flathead crank. Have tried everything from 65 lb ft torque to 100lb ft torque Jimbo, nothing has held. The 100lb held longer than the lower torque numbers did, but still slipped after about 30 hard laps on the track. Engine is an absolute beast when it holds time, I really need to get this issue fixed, several big RWYB races coming up soon in my area and I need my engine to perform right! I have a feeling a new flywheel will fix this issue
 
Sorry I missed the part about what brand of flywheel it is. Actually, if it's a Briggs PVL wheel I doubt that it is cracked but since someone else brought it up I thought I'd add the info about some simple test methods. However, I'll also say that there are more sophisticated and better / safer test methods.
Realize that an exploding flywheel can be lethal
 
What are the better methods? Im always interested in learning something new Jimbo, im still learning these animals everyday. I've never seen a steel hub on a flywheel wear out before, i didnt even know that was possible but after lapping it over and over and over, the back of the flywheel is almost sitting against my block support, so i have no choice but to ditch that flywheel and put a new one on it. I am guessing all the lapping has made the taper on the flywheel so big that it can no longer mate to the crank good enough to hold, does that make sense to you, or is that normal? How can i tell if the crank taper is worn beyond spec from the lapping? Thats what i am worried about at this point is that the crank taper is worn out like the flywheel was. Im hoping the new flywheel fixes this issue, if not i have a new crank i can put in it if i have to, but am hoping not to have to go that route because then ill have to buy new rod bearings for the crank as well, i have a set of the .005 undersized rod bearings in it now since the crank is a seasoned crank and was worn a little, so i needed those bearings to get the proper rod clearance.
 
Roofer Dude said:
Pretty simple to cut a key way where you need it ..... or should I say Broach a key way .
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I know it is simple, but the key is not what holds the flywheel in place, the key is just there for reference, the taper is what locks the flywheel in place and holds it there. And for that reason, i see no point in spending the extra money to have a keyway broached in the crank when i can set the timing wherever i want it with a timing light, and lock it down with red loctite and torque it. Builders have been doing this for years without key's, if they thought they were needed they would be cutting keyways and using them, i trust their opinions and experience.
 
Jimbo said:
Try the ring test. Suspend the flywheel by a string and tap it with a wrench. If it makes a dull thud noise be very suspicious. If it rings like a bell that's s good sign. Compare with another good / new part. A Talcum powder test is also a good indicator of a crack.
Neither of these are fool proof tests but have worked very well for me and others for a very long time.
Click to expand...

Jimbo, what is the ring test telling you, if it rings or makes a dull thud? That isnt making much sense to me but im just not understanding what the test tells you though
 
W5R said:
I know it is simple, but the key is not what holds the flywheel in place, the key is just there for reference, the taper is what locks the flywheel in place and holds it there. And for that reason, i see no point in spending the extra money to have a keyway broached in the crank when i can set the timing wherever i want it with a timing light, and lock it down with red loctite and torque it. Builders have been doing this for years without key's, if they thought they were needed they would be cutting keyways and using them, i trust their opinions and experience.
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That is obviously not working for you , I think Jim broaches flywheel for $25 ... cheaper than flywheel or crank...... just a thought .
 
Roofer Dude said:
That is obviously not working for you , I think Jim broaches flywheel for $25 ... cheaper than flywheel or crank...... just a thought .
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It held all last season without an issue or a single slip. Engine had to come apart to sleeve the block, I didn't get it lapped good enough or torqued good enough when I rushed putting the engine back together to make the first race of the season, which is what caused it to slip the first time, my fault completely. Since that happened, it has not held time no matter what I have done, until I realized that the taper on the flywheel has worn so much that the flywheel now almost sits against the block support on the block. I am not going to have a keyway cut in the crank in attempt to fix an issue that I know is the flywheel, that makes no sense to me when the key is not what holds the flywheel in place.

Are you trying to say the key is what keeps the flywheel from slipping? Sure it may be just $25 to have a keyway cut, but you are leaving out the shipping cost there and back, which is another $25-30 if not more for a heavy crank. Ill replace the flywheel, and if that doesn't fix it, ill replace the crank also. I am not relying on a thin piece of metal to hold a flywheel in place at 9500+ rpm on an open engine, sorry. I only paid $50 for a new PVL flywheel...that seems pretty reasonable to me to fix the issue the right way
 
W5R said:
Jimbo, what is the ring test telling you, if it rings or makes a dull thud? That isnt making much sense to me but im just not understanding what the test tells you though
Click to expand...

Ring testing an iron part will help verify that there are not cracks present. Really not applicable to aluminum... But we do a lot of ring testing on our parts at work (foundry) that are prone to cracking through our process. In the past one crankshaft per hour was ring tested at Briggs and Stratton foundry to verify ductility.
 
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