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Discussion Starter #1 (Edited)
After having broken one engine by starting after a backfire and having the tensioner fail, resulting in bent valves, etc., when mine backfired today, knocking the plenum and hoses loose, I don't want to start it until I have checked the tensioner. I have never taken it off before and will appreciate any help on removing and inspecting it. This is a 1984 GTV-6. Thank you, alfaron[email protected]
 

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First, let me say smart move not trying to restart the engine after a massive backfire.
More specific info about your engine would probably be helpful (year, last time valves/cams/timing chain adjustments were done, carbs vs spica, non-stock modifications if any...).
I don't beleive you actually want to remove the tensioner but adjust it.

I am sure there are several conditions that could cause backfiring and hopefully some other bbers will pipe up and supply some addtional info or correct me if i am wrong:eek:.

I recently dug into my 2.0liter spica engine (1973) and can suggest the following steps based off of my engine (almost identical to other seventies 2liters)
If you suspect the timing chain (i am assuming your car has a chain not a belt) needs adjustment you need to check to see if the timing chain has excessive slack.

Remove the valve cover and see if the timing chain deflects no more than approximately 1/8 to 1/4 inch (3 to 6mm).

This step above is a quick and simple check. If there is significant deflection you need to proceed with caution and follow the steps for both timing chain tension adjustment AND camshaft timing alignment.
Cams not being timed properly can cause backfiring or worse as i'm sure you know. A loose timing chain can cause the cams to be out of alignment.

You should be able to find on the board here steps for both timing chain and camshaft adjustment.

Just word of caution: if the chain needs adjustment, make sure the camshafts are close to proper alignment before making adjustments to the timing chain tension. Cams way out of alignment can easily cause major engine damage.

Tightening the chain is fairly simple but you MUST make sure your camshafts are aligned properly before attempting to start the car.
Tighten the chain first, Time the cams second.

Tightening the chain on my engine was fairly straight forward.
Remove valve cover, loosen but do NOT remove timing chain tensioner BOLT on front of engine block (?14mm?). With transmission in fourth gear, rock car foward and back until chain picks up tension. Tighten bolt (don't over due it). I don't have a torque setting but tight, not outrageous or anything as you can damage the tensioner. My timing chain tensioner took a little while to 'pop' out but once it loosened up it was easy to notice how well it would take up the slack in the chain.

Once the timing chain tension is correct with bolt retightened you should rocked the car back and forth a bit, while in 4th gear, to double check and make sure it really is tight.
You then need to check your camshaft timing.
(again, there are definitely full and detailed descriptions on the board for how to do this)
With the number one piston at top dead center, (both valves should be closed and number four cylinder valves open, a dial indicator is VERY helpful for this), timing mark on crank pointing to P, and distributor rotor pointing to the Number One spark plug
both camshafts, intake and exhaust, cam lobes for the number one cylinder should be pointing out (away from the center of the engine) and the timing mark on both camshafts should line up with marks on caps.

Adjusting the cams is not terribly difficult but you definitely want to read up on it before attempting and the camshaft tool is definitely worth the 15 bucks or so it costs (iap, centerline...).
Again, Make sure your cams are properly aligned before attempting to start the engine.

Hope this helps.
 

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Discussion Starter #3
timing belt tensioner

Thanks for the reply. My error in not noting that this is a 2.5 litre v6, GTV6, 1984 vintage. Thank you though for the trply. Ron Johnston
 

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This happened to me after a mechanic set the timing up wrong.


probably timing needs adjusting. You shouldnt be able to twist the belt through more than about 30 degrees travel if the tension is right whilst not running. take the cover off and visually inspect. make sure belt has not slipped a tooth.and tensioner is correct (if its a mechanical tensioner there will be no issue, but the hydraulic ones fail every 20,000 or so, look for excessive oil) if ok, Remove the plug leads and plugs ( to eliminate compression) and turn over on crank nut a few revolutions to see all is free. if ok, turn over on the starter a few revolutions. if all still ok , set n01 cylinder, check timing marks on pulley are correct, hook it all up fire her up,and set the timing up.
 

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I don't know if this applies to you, but a big cause of backfire and blown plenum on startup is caused by pressing the gas pedal when starting the car. Old habits die hard, and it took me a few plenum blow-offs before I learnt how to start my GTV.
 

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Hmmm. Bummer. Your work is cut-out for you. This is no quick "visual" sort of thing - Unless you like to gamble. First, I'd say get a shop manual or CardisC for this model (or Milano). They're indispensible.

I agree that most likely your timing is off, or advance disconnected or something (coolant sensor), perhaps aux air device not functioning right (all these can make you too rich for too long). Normally what I'm going to say isn't all necessary - if you know your car and feel confident about certain things.

Reason I say that your work is cut out is because to be 100% sure your #1 is at TDC, you'll need to remove the spark plugs, valve covers and timing belt covers - which means you'll need to remove a bunch of stuff on top of the engine too. Once removed, turn the engine over till the timing mark on the crank is aligned, the dizzy is pointing to #1 cyl, and the scribes are aligned on the cam/s. THEN check your belt and tensioner. Reset them properly. Put it all back and start her up.
 

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Excerpt from Shop manual

This will explain why you have to remove your valve covers. If you're certain they're right (recent belt replacement done right) then you really don't have to. Belts usually only jump 1 or 2 teeth. However, if you just bought it and it's never run right, then I advise it removing the covers. Also, it's possible that you could be 180* off and your crank timing mark and distributor will be aligned. Anyhow, here's a pic. Hope it helps.
75-01-088-86.jpg
 

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Just a tip: Check your ignition (cap, rotor, wires) for old age with regard to the backfire. This is the most common cause, IMO. I have seen this firsthand. The plug wires are a prime suspect. an intermitant short will blow the plenum off, no doubt. Its worth thinking about. Good luck with the belt timing!! :)
 
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