[Fot] Weird Race Weekend Question

Tue Nov 26 07:28:38 MST 2019

 That's about normal, why in the sam hell are you using that heavy ass double chain set up?? Come on man get it together.

    On Tuesday, November 26, 2019, 08:29:26 AM EST, Robert Lang via Fot <fot at autox.team.net> wrote:  

  Hi - They usually "jump" a tooth on overrun, or at least that's my experience. Or it can happen on a backfire... I had a Pontiac with a V8 back in the day. The exhaust pipe broke before the muffler, so it had a really kool rumble sound. I used to take it out at night and drive exit ramps at "stupid speed" and then downshift the auto trans one gear to get the koolest sound... not to mention "power-off oversteer".  Drift City. After one of these excursions, the engine became very hard to start. I took the car off the road and sold it to a friend. About a month later, he called me up all pissed off and wanting his $600 back because he had to fix the timing chain.
Never sold a car to a friend or associate ever again.
;-)
But in addition to the new chain and tensioner, take a close look at that crank gear and make sure the "troughs" don't have a burr or the points aren't sharp, either would indicate wear and you don't want that.
I don't recall a spec for play in the chain, but you want "as little as possible". If you can get the cam gear onto the cam easily with the chain threaded, that's too loose.

C ya,Bob Lang

    On Tuesday, November 26, 2019, 7:54:29 AM EST, Mathieu W. Huovinen <maddhatt69 at aol.com> wrote:  

Bob and FOT,

I'm beginning to suspect a combination of a weak chain tensioner and an engine harmonic that may have caused it. Attached a pic of the play in the timing chain..about 1/2". Is that too much? If so, Ted, I'll be contacting you shortly. Chain is about two years old, maybe 6 weekend s of racing on it. New chain tensioner from Moss should be here today and I'm interested in seeing the difference in spring arch between the original single chain tensioner and the new TR6 double chain tensioner. Stay tuned!

Mathieu 
On Monday, November 25, 2019 Robert Lang <robertlangtr6 at yahoo.com> wrote:
 Hi - I've seen this before. Mostly on American V8's but the principle is the same... It's almost always a loose chain or worn teeth on the crank gear. If the  crank gear has really sharp teeth, the gear is probably worn. Note that this is really easy to overlook. And I've had this problem with TR6 engines a couple of times. Especially if you sourced the inexpensive gears. Seems like the hardening of the metal is wrong on some of the parts out there.

That said, the numbers look like you jumped more than one tooth. If the "jump" occurred on the crank end one tooth is about 17 degrees (360/21 teeth). Your mention of 150ish for your lobe center sound more like more than 34 degrees or retard, the progression would be (roughly) 104 - good, 121 - not good, 138 - bad, 155 - really bad, etc. Note that I have seen engines run with more than 30 degrees of retard, but they ran very poorly!
I'd double check your crank gear for wear... actually, I'd just replace it along with the tensioner. Note that the current chain tensioners seem to be not as good as the OEM ones as the new ones wear fairly rapidly.
On the plus side, at least you didn't bend a valve in the process.
C ya,Bob Lang339-927-4489

    On Sunday, November 24, 2019, 10:38:49 PM EST, Mathieu W. Huovinen via Fot <fot at autox.team.net> wrote:  

 Fellas,
Sounds like we have the bearing cap strap issue resolved...who is up for another mystery? Has anyone ever has their timing chain skip a tooth??
Final race on Saturday at the Turlkey Bowl this weekend at Summit Point. Triumph Spitfire..1296 engine. Double roller chain set. Car was running well all weekend, was out twice earlier that day. We leave false grid for the to set up for the first lap and I begin to accelerate. All of a sudden the car just dies and I coast off the track even before turn one. On the side of the track I couldn't start the car. In my mind I'm thinking my perrtonix distributor just took a shit. Got towed in and all I'm thinking in pertronix. I swap in a points distributor and nothing. Perhaps my coil? Swap in a new coil. Nothing. Plugs perhaps? Swap in a good set of NGKs. Nothing. Not even a cough out of the engine. By this time I had run down the battery from trying to start it so much. At this point I was jumping the racecar battery from my Tundra truck battery thinking perhaps a weak spark from a shot battery. Nothing. Was getting plenty of fuel because the plugs were wet. I even pulled and cleaned all the jets out of the Weber 45 DCOE just to make sure I was getting correct fuel. Fuel. Air. Spark. COMPRESSION. This next day (this morning) I did a compression test at the track. 80/70/70/70. What the heck? Thats not a blown head gasket..the cam HAS to be out of timing. I spent the majority of the 5 hour drive home trying to figure it out. Got home, car off trailer, straight to work. Pulled radiator, pulley, timing chain cover. No damage. Find TDC and put on my degree wheel. Pulled rockers and set dial indicator on #1 intake. Tuned engine over to where cam sheet says where #1 centerline is- 104 degrees after TDC while watching dial indicator. Went past 104 and dial was still climbing. Made it to to about 150ish degrees past TDC til indicator started to drop back down so I know I had went right past the peak of the lobe. Pulled chain off carefully and rotated camshaft until I found peak of lobe and moved crank back to 104 and set the chain back on...about one tooth  Put rockers back on and checked compression on #1. 160 PSI. That's as far as I got before my wife came down to yell art me. It was already 2130 at this point. More tomorrow as I put it back together. 
Thoughts? Ideas? Can the timing chain "float" at high revs? Thank-you in advance for any input!
V/r,
Mathieu Huovinen_______________________________________________
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