Starting problems

[eheal6520]

Hi Guys
My 2012 S10 with 135k miles on it suddenly would not start. I tried all the suggestions here (fuses, WOT, etc.). Checked the diag codes and only get a 14. Finally took it to the dealer for a look see and they confirmed that I have good spark (put in a new set of plugs) and the injectors are working fine (I had pulled, cleaned and tested them). What they did find is a compression problem, "left cylinder has 115 psi and right cylinder has 65 psi should be 96 psi". I would have left it with them but $3200 in labor just to find the problem is a bit stiff. I have not recreated the compression test so I am trying not to suspect the dramatic, bad rings, cracked piston, etc. I decided to check if one of the valves was stuck open causing the low compression. What I found is the exhaust cam shaft way out of alignment to the tune of 4 links on the cam chain. Unfortunately in the case, my general attitude of "if it ain't broke, don't fix it" appears to have gotten me in to trouble.
What I would like to know is, is the book correct or is there some sort of undocumented update. To my untrained eye it looks like it skipped 4 links. I have read about the cam chain tensioner and since mine is OEM I have ordered a new one. See the pictures below. Any advice would be helpful. Thanks
intake cam gear (fyi the chain is loose on the left because I had removed the tensioner before this picture)

intake cam alignment hole

exhaust cam gear - not like the manual

K alignment gear

Page 5-22 from the manual with the alignment

 

[Sierra1]

I have a Gen II, so the CCT is not an issue. But, IIRC, on the Gen I's the CCT was supposed to be replaced w-a-a-a-ay before 135k mi. It's time to talk to TABASCO.

 

[holligl]

Fortunate if you didn't do more damage skipping links. Order a new CCT, either OEM or a cheaper manual. Guessing you will need to remove one or both cams to get it lined back up per the manual. How long since valves were checked? Once you get it back together they should be checked and adjusted if needed. Unfortunately multiple disassembly/reassembles are likely if adjustment is needed. Take your time and check/double check alignment marks.

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[gv550]

The T12 is an interference engine, meaning the valves will hit the piston if cam timing is wrong. This could cause valves to bend which would result in low compression. You should be able to check this by measuring valve clearance, if a valve is bent the gap will be way beyond the maximum.

 

[Tenman]

I bet it ran like $hIt. Your cct should have been giving you an advanced warning miles ago with a nice rattle on start. Mine started at about 10k. I would've thunk you could hear bent valves making some noise. If you do a valve job yourself this link has some good info on that and lots of tenere maintenance with GOOD pictures. scroll to the bottom and click tenere. https://thetenerist.wordpress.com/

 

[Jlq1969]

If the engine does not start, how did the mechanic measure the compression? ... would he have disconnected the automatic depressor? ... ... and if he had disconnected it, he should have seen the displaced marks. Maybe, I'm missing something ……
I see the marks, the intake would be fine… ..but the exhaust cam is advanced with respect to the mark of manual, and if the chain were to skip (due to tensioner failure)… the Cam should be late. (if he is late, he has almost made a full turn, more than four teeth


Did you, at some point, turn the bike back with a gear engaged and the engine off??

 

[Sierra1]

The T12 is an interference engine, meaning the valves will hit the piston if cam timing is wrong. . . .

I've always heard that with an interference engine, when the timing goes. . . . it cost more to repair the motor than it's worth. Is this one different?

 

[eheal6520]

I have a Gen II, so the CCT is not an issue. But, IIRC, on the Gen I's the CCT was supposed to be replaced w-a-a-a-ay before 135k mi. It's time to talk to TABASCO.

My bike has been noisy since I bought her in 2012, I always thought this was a result of having solid lifters. When she would not start I ground on the starter so much I burnt it out and had to replace it. During all this time I haven't felt or heard anything unusual while it spun. This is the first time I have cracked any covers on the bike. Normally I change the oil every 3K miles, tires when needed and spark plugs 4 times. I have had her not start on a couple of occasions but the WOT technique has always worked.

 

[eheal6520]

Fortunate if you didn't do more damage skipping links. Order a new CCT, either OEM or a cheaper manual. Guessing you will need to remove one or both cams to get it lined back up per the manual. How long since valves were checked? Once you get it back together they should be checked and adjusted if needed. Unfortunately multiple disassembly/reassembles are likely if adjustment is needed. Take your time and check/double check alignment marks.

Sent from my SM-N950U using Tapatalk

I have never adjusted the valves but will definitely check them more in the future. I have ordered a OEM CCT and am definitely taking it slow.

 

[eheal6520]

The T12 is an interference engine, meaning the valves will hit the piston if cam timing is wrong. This could cause valves to bend which would result in low compression. You should be able to check this by measuring valve clearance, if a valve is bent the gap will be way beyond the maximum.

Once I get the exhaust cam shaft realigned I will check the clearances, hopefully nothing got bent.

 

[eheal6520]

I bet it ran like $hIt. Your cct should have been giving you an advanced warning miles ago with a nice rattle on start. Mine started at about 10k. I would've thunk you could hear bent valves making some noise. If you do a valve job yourself this link has some good info on that and lots of tenere maintenance with GOOD pictures. scroll to the bottom and click tenere. https://thetenerist.wordpress.com/

Nope, no advanced warning that I recognized. I rode her home from work (32 miles) and parked her like normal and the next day she wouldn't start. Starter spun the engine, but no kick. Thanks for the link, good stuff there!

 

[eheal6520]

If the engine does not start, how did the mechanic measure the compression? ... would he have disconnected the automatic depressor? ... ... and if he had disconnected it, he should have seen the displaced marks. Maybe, I'm missing something ……
I see the marks, the intake would be fine… ..but the exhaust cam is advanced with respect to the mark of manual, and if the chain were to skip (due to tensioner failure)… the Cam should be late. (if he is late, he has almost made a full turn, more than four teeth


Did you, at some point, turn the bike back with a gear engaged and the engine off??

The mechanic used the starter to spin the engine. It spins but wouldn't kick, cough or otherwise attempt to start. No he did not crack any covers, just removed the coils and spark plugs. He did state that there was no obvious damage to the valves or pistons. Not sure, but I think he scoped them for a limited visual. "Did you, at some point, turn the bike back with a gear engaged and the engine off?? ", nope just attempted to start it with the starter motor.

 

[eheal6520]

The plan at this point is to move the exhaust cam back in to alignment per the manual. Once done, manually turn everything to make sure I haven't screwed it up any more, then check the valve clearance hoping everything is not way out of wack. If all goes well, I will attempt another compression check... Hopefully the compression check will at least be more balanced....

 

[patrickg450]

$3200 for labor only to diagnose a fault? How many hours?

 

[eheal6520]

$3200 for labor only to diagnose a fault? How many hours?

When I called for an update I was told a no start diagnostic was performed. It consisted an injector test, a coil test and a compression test. OK, I asked how much do I owed so far.. $580. I kind of went thru the roof... $580 for basically a compression test! Worse yet, I asked for a ballpark labor estimate when they said an engine teardown was required for further diagnostics. That's where the $3200 (24hr labor) comes from.. half to tear it apart to figure what's wrong and the other half plus parts to fix it and put it back together.. When I got there to pick her up the diagnostics bill came down to $140 and now that I have calmed down the big money was probably more of a deposit on the actual labor than possible actual cost. This especially since it only took me a couple of hours to be able to take the photos. Sorry for the windy explanation...... Anyway I am now waiting on parts to put her back together so I can do a compression test... crossed fingers no bent valves....

 

[holligl]

So did you order an OEM or manual CCT?

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[Jlq1969]

When I called for an update I was told a no start diagnostic was performed. It consisted an injector test, a coil test and a compression test. OK, I asked how much do I owed so far.. $580. I kind of went thru the roof... $580 for basically a compression test! Worse yet, I asked for a ballpark labor estimate when they said an engine teardown was required for further diagnostics. That's where the $3200 (24hr labor) comes from.. half to tear it apart to figure what's wrong and the other half plus parts to fix it and put it back together.. When I got there to pick her up the diagnostics bill came down to $140 and now that I have calmed down the big money was probably more of a deposit on the actual labor than possible actual cost. This especially since it only took me a couple of hours to be able to take the photos. Sorry for the windy explanation...... Anyway I am now waiting on parts to put her back together so I can do a compression test... crossed fingers no bent valves....

Before checking the pressure, it would be interesting to check that the revs of the starter motor are not "below" the 250 rpm recommended in the manual ... otherwise the automatic decompressor will be activated and the measurements may be wrong.

 

[eheal6520]

So did you order an OEM or manual CCT?

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I ordered the OEM

 

[eheal6520]

Before checking the pressure, it would be interesting to check that the revs of the starter motor are not "below" the 250 rpm recommended in the manual ... otherwise the automatic decompressor will be activated and the measurements may be wrong.
View attachment 83842

I have both a new starter (well new to me, 2012 ebay) and a new battery. I would hope they would meet the specs, otherwise I haven't a clue as to how to check the starter rpm. Wouldn't that more likely be the engine rpm?

 

[Jlq1969]

I have both a new starter (well new to me, 2012 ebay) and a new battery. I would hope they would meet the specs, otherwise I haven't a clue as to how to check the starter rpm. Wouldn't that more likely be the engine rpm?

yes… ..the engine revolutions, using the starter motor…. There is no way to know that it turns at 250 rpm (the tachometer does not have that scale),maybe using a multimeter that counts rpm by intercepting the signal from the coils….. but it should be enough with a battery with 100% charge/CCA, and a starter motor in perfect condition. The service manual clarifies obvious things to measure compression "hot engine"…. ”throttle wide open”… ..and something that is more complicated 250 rpm (I calculate that at those rpm, the automatic decompressor is already deactivated)… ... there is no other choice but to suppose that with a good battery / starter, those rpm are reached
But it would have been good if they clarified "and no less than this" ... ..and we would know that we have no margin down. I say this because a "slow start" (due to a low battery or bad CCA) is common in the S10, and perhaps at 230 rpm the decompressor is still activated