[Fot] Weird Race Weekend Question

Mon Nov 25 05:14:06 MST 2019

Gents,
I do have an adjustable cam gear and it was tight. Double roller, cam gear, and crank gear all sourced from Jigsaw Racking UK about two years ago. Maybe 5 weekends worth of use. I did reuse the chain tensioner that was in the timing chain cover (unknown use- likely stock from the early 70s) and I will admit it is the tensioner for a single chain- it also seems pretty worn. I am ordering a double chain tensioner from Moss this a.m. and see how it differs and will swap them out. Thanks for the responses!
Mathieu

-----Original Message-----
From: Robert Lang <robertlangtr6 at yahoo.com>
To: fot <fot at autox.team.net>; Mathieu W. Huovinen <maddhatt69 at aol.com>
Sent: Mon, Nov 25, 2019 6:21 am
Subject: Re: [Fot] Weird Race Weekend Question

 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_______________________________________________
fot at autox.team.net

http://www.fot-racing.com

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