91 454 CID... another year on top half?

My starboard engine is a 1991 Crusader LH 454 CID.
I have 1200 hours so I performed a compression test when doing tune-up.

1 148
3 135
5 135
7 140
2 145
4 144
6 144
8 147


Question 1: What is the danger to running this season (another 100+ hours) and waiting until the winter season to redo the top half?

Also I have a new snap-on advanced timing light so I was able to take a look at the my ac delco e.s.t. advance curve.
The light flashes every other signal so I should have been able to get a good reading. The curve matched the manual that I have until I got up to 3200 RPM and above. At that point I had the mark on the HB bouncing back a forth about 20 degrees!

Question 2: What would generally cause that? I replaced cap a rotor. Replaced new proper gapped plugs. I replaced wires two years ago. Looked scary to see that.

your numbers look acceptable. I'd look at the vacuum numbers before judging the condition of the top end. the only danger is something breaking and that isn't on the likely side unless you prefer lots of WOT operation. the only drawback is the potential fuel savings from having things optimal.

i don't understand "flashes every other signal"....care to ellaborate?

a 'jumpy' timing mark can be caused by a few things. being as things were 'good' until max advance, I'd concentrate on having a good, clean trigger to the light. trying moving the sensor so it as far as possible from the other wires, plug leads in particular.

Maybe sales gimic... The strobe flashes every other time the sensor gets triggered. The idea is at high RPM you get clear picture. You don't have to explain the speed of light to me, but snap-on is a quality tool manufacture.

Do I have to worry about the spread of 13psi between worst and best compression reading?

I did move the sensor. Its close to the plug as can be. Could cap and rotor be arching as it looks like the triggers from the two contacts on either side? The cap and rotor are merc from local marine store. I'd like to thinmk its the "tester"

slauder said:

The curve matched the manual that I have until I got up to 3200 RPM and above. At that point I had the mark on the HB bouncing back a forth about 20 degrees!

Question 2: What would generally cause that? I replaced cap a rotor. Replaced new proper gapped plugs. I replaced wires two years ago. Looked scary to see that.

Click to expand...

I would seperate, as much as possible, wire #1 from the others running alongside. You might be getting a trigger from another plug wire.

I've been told that if the compression between cylinders is within 10% of each other you are good. Based on that I don't think you have a compression problem.

Actually, GM says all cylinders within 70% of the max value, on a cold engine.

Check with the manual to see if the 'feature' can be disabled.

Snap-On used to be a quality tool manufacturer. Their wrenches and sockets are superior quality but very pricey. Due to market pressures, they are a bit more willing to 'sell' their 'name' to be placed on some "less than stellar" products. BTW, they are NOT the only ones; Craftsman and Fluke are two other well recognized brand names that are just a guilty.

Adjacent plug leads are 45 degrees apart on the cap - that equals 90 degrees of crank rotation. The triggering is not likely to be from the adjacent leads.

You can also add an inline spark tester to make sure the plug is firing every time.

My newest philosophy on tools is that I try to buy good socket set, box wrenches and screwdrivers for everyday stuff. Once something falls into a minimal use category and does not really require great quality, I check out the importers. From building bikes, I have a pretty darn good collection of higher end tools. BUT the costs in the 1980's and 1990's was a bit different as was my income ratios.

I think as mentioned, unless something goes berserk and breaks, you should be more than fine