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I recently rebuilt my 455 Olds and I'm not sure if I have a timing problem or something else. I'm not sure what any of the timing marks on the indicator are according to degrees except 0, but I have it set on the last notch on the indicator. I have been easy on it while breaking it in for several hours. Today, I was cruising at 3K rpm and decide to open the 4 bbl for a second or 2, I gave it about 3/4 throttle and at a little over 4K rpm as soon as the power hit, it started pop/crack/backfire. Where should I be on the timing indicator? I'm pretty sure it's a timing issue, but I could be wrong? Thanks for any input!
 

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Idled best with lots off timing but tended to have some hot start issue. I ended up moding the mech advance so it had 32 while cranking all in @ idle...You will need to come up with an adjustable timing light and using the tab and mark on balancer is kinda worthless without checking their accuracy.Somebody used to make tdc checker...screws into #1 plug hole..very carefully rotate engine over until piston just touches tool. put a mark on the balancer where the tab says 0....rotate the other direction careful...until piston touches tool...mark balancer again @ 0....exactly half way between marks, lined up with 0 on the tab is tdc #1
...or #6.......mine was only off 4*......As far as how i came up with 40*
total....i put a load of 92 octane and stop watched it several dozen time from 1500 to 5K and kept twisting the dizzy until i came up with the best number.....actually 40* and 42* were the same and i picked 40* for a bit of safety margin...although olds doesn't seem to have much of a detonation problem, with 92 octane it will have an obvious part throttle misfire
 

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Thanks Sold Honda Bought Hondo!

Jetboatperformance - I am usually around 800' in altitude give or take 100 depending on where I'm boating. Compression ratio is stock, but I'm not sure what it is, the engine is a 1973 model with J heads. The carb is a Holley 750 double pumper, intake manifold is Edelbrock Performer and I run 93 Octane fuel and have bassett over transom heads, no baffles. The cam is 270*/.501 if I remember correctly. Anything else that would help, let me know! Thanks!
 

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Thanks Sold Honda Bought Hondo!

Jetboatperformance - I am usually around 800' in altitude give or take 100 depending on where I'm boating. Compression ratio is stock, but I'm not sure what it is, the engine is a 1973 model with J heads. The carb is a Holley 750 double pumper, intake manifold is Edelbrock Performer and I run 93 Octane fuel and have bassett over transom heads, no baffles. The cam is 270*/.501 if I remember correctly. Anything else that would help, let me know! Thanks!
There are/were a couple options on OEM pistons from that era this can be told by the "dish" in the top . you may be able to see in the combustion chamber with a good bright flash light , the low comp (8+) is around 5/32 while the Higher (10+) is closer to 3/32 as I recall. You could run significantly more total timing with the low , but with modern fuel the Higher compression can detonate among other issues , Not sure your "popping" is neccesarily timing related IMO

BTW your will likley need mods to the advance weights to get 30+* of total (without having to run an enormous amout of initial)
and ditch the vac advance
 

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There are/were a couple options on OEM pistons from that era this can be told by the "dish" in the top . you may be able to see in the combustion chamber with a good bright flash light , the low comp (8+) is around 5/32 while the Higher (10+) is closer to 3/32 as I recall. You could run significantly more total timing with the low , but with modern fuel the Higher compression can detonate among other issues , Not sure your "popping" is neccesarily timing related IMO

BTW your will likley need mods to the advance weights to get 30+* of total (without having to run an enormous amout of initial)
and ditch the vac advance
The olds t/r 660's deal i have for my hydro needs major lead to get a decent idle out of it.With a normal curve and 22* initial and set the idle @ 900 in gear neutral idle was 1600 and it was lazy off idle. With 36-38 initial i got it down to 600-650 in gear....kinda necessary to even get close to no wake speed...and it would hold that idle all day and 1000 out of gear and from 1k in gear i can pin the gas and no hesitation... But it
did the timing stall every once in a while...I think i ended up with an little allen head bolt and a nylock through the advancer base plate to limit the advance to 6-8 degrees...mostly because it would start so quickly you couldn't hear the starter run....and used 2 really loose springs...just enough to pull the advance back when the dizzy wasn't turning
 

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I recently rebuilt my 455 Olds and I'm not sure if I have a timing problem or something else. I'm not sure what any of the timing marks on the indicator are according to degrees except 0, but I have it set on the last notch on the indicator. I have been easy on it while breaking it in for several hours. Today, I was cruising at 3K rpm and decide to open the 4 bbl for a second or 2, I gave it about 3/4 throttle and at a little over 4K rpm as soon as the power hit, it started pop/crack/backfire. Where should I be on the timing indicator? I'm pretty sure it's a timing issue, but I could be wrong? Thanks for any input!
The last time I was "shootin ducks" I had an intake valve too tight....good luck.
 

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Discussion Starter #11
The olds t/r 660's deal i have for my hydro needs major lead to get a decent idle out of it.With a normal curve and 22* initial and set the idle @ 900 in gear neutral idle was 1600 and it was lazy off idle. With 36-38 initial i got it down to 600-650 in gear....kinda necessary to even get close to no wake speed...and it would hold that idle all day and 1000 out of gear and from 1k in gear i can pin the gas and no hesitation... But it
did the timing stall every once in a while...I think i ended up with an little allen head bolt and a nylock through the advancer base plate to limit the advance to 6-8 degrees...mostly because it would start so quickly you couldn't hear the starter run....and used 2 really loose springs...just enough to pull the advance back when the dizzy wasn't turning
When I put the distributor in, I set the distributor by eye to get it started to see if it was going to run. It was very hard to crank, but when it fired up it was the same as you said, so fast you didn't even here the starter or the engine roll over. It fired at the snap of the finger so I knew the timing was off. I'm guessing I took it back 12-14* to get it where I have it now. It's possible I took too much away and the indicator is useless to use as a reference point. This might be something I just need to do some trial and error with and find out where it runs best and leave it.

jetboatperformance - Ok, I have the low compression pistons based off of your info.

Thanks everyone for your help! I will start troubleshooting with your suggestions!
 

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When I put the distributor in, I set the distributor by eye to get it started to see if it was going to run. It was very hard to crank, but when it fired up it was the same as you said, so fast you didn't even here the starter or the engine roll over. It fired at the snap of the finger so I knew the timing was off. I'm guessing I took it back 12-14* to get it where I have it now. It's possible I took too much away and the indicator is useless to use as a reference point. This might be something I just need to do some trial and error with and find out where it runs best and leave it.

jetboatperformance - Ok, I have the low compression pistons based off of your info.

Thanks everyone for your help! I will start troubleshooting with your suggestions!
That is exactly where you need to be. Set the timing where it idles best
ie the best throttle response right off idle....and not necessarily the smoothest and put timing light on it...and it doesn't matter if the marks are off...just so you know where it's at. Then take it out and run it and figure out a way to accurately measure it..GPS for top mph or tach for max rpm or stopwatch from 2500 to 4500...and carefully advance the dizzy a little at a time... It should run better and better..and then the same and then worse....back it up to he second 'better' and put timing light on it.
The first number is base/initial timing..if it will start clean an easy that is the number you use...if not back the timing until it does...The second number is TT..Total timing and the difference between the 2 numbers is how much you need to limit the dizzy from advancing.

Just make sure you are nice to olds motor...They do not last if ya rev them past 5000 rpm...they won't last long if ya rev them past 4500 for extended periods...Make sure you have an accurate oil pressure gauge
and watch it like your future boating budget depends on it.:)hand
 

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Maybe I'm stating the obvious but if you just recently rebuilt this motor, you (or the shop that assembled it) should know exactly where your timing marks are?
If you are confident the timing marks on the timing chain are correct, did you degree the cam and check the timing marks on the balancer in relation to TDC of the engine and the cam position?
Is it a new/aftermarket balancer?
If run into a lot of aftermarket balancers that have the timing marks off.

Other issues could be ignition related or valve adjustment (too tight or too loose).
Fuel system/carb should normally not cause backfiring-
How is the engine vacuum at idle? Perhaps you have a vacuum leak somewhere?
 

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Discussion Starter #15
Maybe I'm stating the obvious but if you just recently rebuilt this motor, you (or the shop that assembled it) should know exactly where your timing marks are?
If you are confident the timing marks on the timing chain are correct, did you degree the cam and check the timing marks on the balancer in relation to TDC of the engine and the cam position?
Is it a new/aftermarket balancer?
If run into a lot of aftermarket balancers that have the timing marks off.

Other issues could be ignition related or valve adjustment (too tight or too loose).
Fuel system/carb should normally not cause backfiring-
How is the engine vacuum at idle? Perhaps you have a vacuum leak somewhere?
It is more of the popping and cracking nature. I don't know it if really backfired or not because it's loud in general. The balancer is factory. I'm sure it is a timing problem, but I didn't know how accurate the factor balancer and indicator were. It's possible it could be a valve issue. I'm going to try to adjust the timing this weekend and if that doesn't help, I will check into the vacuum next since the only vacuum leak I can think of could be coming from the intake manifold.
 

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timing problems!

your camshaft might be wiped! check each one of the distribuitor wires at the dist. CAP for a spark, example if #1 has no spark because that lobe of the can has been worn causing detonations on the dist.
 

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The first question is it (the back firing or popping ) coming from the carb and is it consistant , constant and a "stucato" type noise , also has the boat/engine been setting awhile ?
 

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Just went through an Olds 455 rebuild. Had the exact same issue (popping thru carb) at around 4000 RPM. First problem I had was a weak coil. The second and what was my real issue was poor fuel pressure. Had crud in tank thanks to the crap MBTE gas here in the Northeast and old metal tank. Found out by installing fuel pressure gauge and found pressure down around 2-3lbs at times. Olds seems to like 6.5-8.5 lbs of fuel pressure. Replaced old tank with plastic tank and new fuel pump and no more pop and crackling at 4000RPM. By the way take everyone's advice on watching the oil pressure gauge. Am solving my problem with the correct oil pan from Tom at JetBoatPerformance.
 

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If it's a new cam, I'd pull the covers and make sure all the rockers still have full travel when you roll it over. I highly doubt it's timing, but you need to run a dialback style light on it and set if for 36 degrees max. Hopefully you have light enough springs that you can get max timing by 3000 rpms. Maybe lean pop from a weak fuel pump? Olds require a good pump to spin over 4500 without running out of gas.
 

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I had the same exact problem with my Olds, spin it over 4500 and the same pop and crack. I have tried, new fuel pumps, new carb, new hei, hei vaccum adv. lockout, hei coil, hei module, hei weights and springs, new wires, new spark plugs. adjusted valves, adjusted timing all over the place to try to fix it, still does the same thing WOT. POS OLDS!
 
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