ok, wtf....:mad:

[ChrisF]

Thought I lost the timing chain late last season, was driving the car (running just fine) and it just shut off. Verified spark and fuel, no restart. Cranking sounded odd, and the boost gauge would blip during cranking, as if pressure was coming back into the intake. Thought surely the timing chain slipped.

Decided before taking it all apart to do a compression test. Removed both valve covers and the rockers and pushrods to ensure all valves were closed. Removed all 6 plugs for consistent cranking speed. I get these readings: # 2, #3, #6 all over 100 psi....#1, #4, #5 all at 30-50 psi....and they hold that pressure....the low ones dont leakdown like a blown headgasket or a burned piston or valve....

What gives?? Anyone?

 

[gunslinger]

You can't do a compression test with the rockers off. An engine is an air pump, and if you don't allow air in and out , it can't build pressure properly. The readings you're getting are probably from air trapped in the cylinders before you put the compression tester on. If leak-down is okay, I'd put the rockers back on and recheck cranking compression. If it's inconsistent, then pull the timing cover and take a look.

 

[ChrisF]

Hmm never thought of that. Rockers back on and will test. If that holds true and I get say 100+ on all 6, then its gotta be the timing chain...Thanks!

Anyone else?

 

[notacarlo]

Pull the cam sensor, get a flash light and look at the timing set.

 

[bmackinnon]

You can't do a compression test with the rockers off. An engine is an air pump, and if you don't allow air in and out , it can't build pressure properly.

DOH!! :biggrin: just kidding, I'm sorry, just couldn't resist.... I've never heard of someone trying to test compression with all the valves closed.... kinda defeats the purpose!... good luck and report back with the results... If you still have the stock timing set, I bet it stripped all the nylon teeth off the cam gear... and if so, you'll need to drop the pan and clean/remove all the ruins out of there...

 

[ChrisF]

LOL No worries. Someone told me to do it that way for fear of the valves hitting the pistons if the chain is way out of whack. I thought it sounded suspect myself!

 

[joe_schindler]

LOL No worries. Someone told me to do it that way for fear of the valves hitting the pistons if the chain is way out of whack. I thought it sounded suspect myself!

If the valves were going to hit the pistons while you are cranking for a compression test; they’ve already done it.

 

[ChrisF]

update!

Thanks again guys, all 6 cylinders are over 120 psi...so clearly the problem is in the top end. The timing dots appear do not have slipped, and the previous owner did do a timing chain as he indicated. Since the timing chain appears to have not slipped, would losing the cam sensor be enough to make it quit? I was told they will still "batch fire" without it.

Clearly a new cam is in order, (204/214 @.050 112 lsa) is my pick...

I think we found the problem? lol

 

[bmackinnon]

When you change the cam, if you run a double roller timing chain, DO NOT re-install the chain tensioner.... the roller chain will eat the tensioner and send all the debris to the pan to clog the oil pump pickup... not good...

 

[Turbo1dr]

Did you have a high volume oil pump on that engine?

 

[thadeal4real]

a pressure washer will help too

 

[SS_Sean]

a pressure washer will help too

seriously...

 

[novaderrik]

a pressure washer will help too

but that would get rid of all that premium Buick rust proofing..

 

[Turbo1dr]

It had to be leaking extremely bad since the front seal retainer is loose from the timing cover and the rope seal is all eat up. For those people with high volume pumps...that cam gear is what yours will be looking like after a while.

 

[Jerryl]

. . . . For those people with high volume pumps...that cam gear is what yours will be looking like after a while.

I have the utmost respect for all your knowledge and innovative accomplishments, and your kowledge sharing.

I have run a HV pump for +18K miles and never had an issue.
Pump end clearance was set to 0.0015", and main passages opened up.

If the gear alignment is off, or the pump did not spin freely when assembled, or the oiling is insufficient, you most definitely increase the chances of what the pic indicates with a HV pump! Not suggesting anyone needs a HV pump, just sharing an experience. (Probably got lucky :tongue

Surprised no one mentioned this "yet" . . . . To the OP:
Time to pull the motor and hot tank it. Too many metal particles in the motor, for my taste.

 

[thadeal4real]

man might hot tank the car too now ive gone too far sorry

 

[williamsGN]

When you change the cam, if you run a double roller timing chain, DO NOT re-install the chain tensioner.... the roller chain will eat the tensioner and send all the debris to the pan to clog the oil pump pickup... not good...

That is true on the Comp chain, not all double rollers require removing it, in fact some still need it for proper operation.

I also have the HV pump with thousands of miles on it and the engine was just apart, no issues such as above.

 

[ChrisF]

I had a 455 do the same thing with a high volume pump years ago. I guess I shouldn't have been listening to Kenne Bell. Scatter fire the distributor on the expressway made for a muffler turning into a hand grenade!

I am not sure what pump/spring are in this car, this is the way I bought it. I suspect someone put a high volume pump in it. The rope seal was trashed too, but interestingly enough after 2500 miles or so it would only be down a 1/2 quart. So as filthy as it is, I have never had it apart to clean it. Don't worry, I will tidy things up.

I think I am going to run a bronze gear on the cam sensor just like I used to on the 455 to prevent this from happening again.

 

[bmackinnon]

That is true on the Comp chain, not all double rollers require removing it, in fact some still need it for proper operation.

I also have the HV pump with thousands of miles on it and the engine was just apart, no issues such as above.

Comp, Cloyes, Rollmaster, etc. double rollers will ALL eat the tensioner... can you name some examples that won't? or that 'require' the tensioner? The only time I would use a (stock) tensioner would be with the stock chain... please enlighten us...

Also, it's PROVEN FACT that the HV pump puts additional stress on the cam gear (and thrust surface)... simple engineering numbers... does it NECESSARILY result in gear failure? No... do some get away with it? Yes.... but is it an additional (and IMO unnecessary) cause for concern? Absolutely..... 'thousands of miles'?? Let me know how it looks after 80-100k, and maybe I'll rethink it.....

 

[williamsGN]

Actually mine is here with 40K miles on the tensioner, very little wear. JMS racing engines just replaced it as part of the build. Said my current chain required a tensioner unfortunately there was no part number except to say it is a double roller. I'll take their word after building engines since '73, as opposed to those that may or may not have ever put wrench to engine rolleyes: using these a lot just makes you look arrogant/ignorant) We're here to help each other, try to act a little less condescending in most of your posts