Timing w/ vacum gauge

[FreeBeeTony]

I am still not 100% sure if my timing is set correctly. The engine is a Mercruiser 165 IL6 with a Pertronix II conversion kit. The boat is a '78 20' Grady White. The outdrive is a 1.65:1. I initally had a 19" prop and was only getting 3400rpm's at WOT. I switched to a 15" prop and am now running at closer to 4000 at WOT. I thought I should be able to turn a bigger prop....like the 19". I just want to make sure I am timed right. I rebuilt this engine last year, the timing markings on the block are not very clear (the tabs is very rusted). I have heard you can check the timing with a vacum gauge (see previous post , the reply by daveswaves). Has anyone done this? Is it a accurate way of checking timing?

 

[affa]

Re: Timing w/ vacum gauge

Hi<br />Ive read about it on this links:<br /> http://www.boated.com/pop_printer_friendly.asp?TOPIC_ID=47078 <br /> http://users.bigpond.net.au/ergoff/vac1.htm <br />Regards<br />Affa

 

[FreeBeeTony]

Re: Timing w/ vacum gauge

I tried to adjust the timing with the vacum gauge. When I took it out for a test run, it seemed to ping when I opened it up. I didn't like that so I retarded the timing some and the pinging went away. Was the pinging caused by the timing? Or is it possible that the timing was correct and the pinging was caused by the gas. I am running 87 octane.

 

[Rainmaker]

Re: Timing w/ vacum gauge

I used to time my cars this way. But an engine timed with a vacuum gauge will always have too much advance, and it will ping. Seems like you've found this out. I used to then retard the timing in small increments until the pinging went away. Then I would retard it a little more for safety.<br /><br />Detonation (pinging) in a marine motor is a killer. Be very careful. My advice would be to clean up the timing tab and check initial and final timing with a timing light. You'll also need timing tape to do this.<br /><br />What distributor do you have? If it is a Delco you can buy heavier advance weights and lighter springs for a V8 Delco distributor. Moroso Accel, and others make these.

 

[FreeBeeTony]

Re: Timing w/ vacum gauge

I went out and bought a timing light and adjusted the timing to be close to TDC @ 600RPM in neutral in the driveway at normal operating temp. I can't tell exactly where it is set because the timing tab is so corrodid. If I had a good one to compare it to it would be a great help. I used the vacum gauge to fine tune the carb. I was only able to get ~ 17in at 600 RPM's. I think this is in spec.<br />Anyway, I think I was too far advanced. I can't tell how far but I would estimate maybe 6-8 degrees. How much would this affect the performance? Did I cause any damage by running it like this? I only ran it for maybe 2 hours like this. Should my operating temp go down and my RPM's at WOT go up? That's what I am hoping for. <br />I hope to get out sometime this week after work for a test run.

 

[Rainmaker]

Re: Timing w/ vacum gauge

If you caused any serious damage you would probably know it. Long-term detonation will cause things like broken/burned pistons, broken rings, and spun rod bearings. Did you continue to drive it while it was pinging?<br /><br />I used to have a 250 I6 (165hp) Chevy and an OMC drive. Timed it at 6 degrees BTDC at idle. Max advance was about 30 degrees at ~2500 RPMs (with heavier distributor weights and lighter springs). WOT was about 4200.<br /><br />Generally speaking, the more advance your engine can stand the better, with a max at about 32 degrees (depending on engine compression ratio and fuel). But you have to be very careful not to go too far. You can time an engine by trial and error or vacuum gauge, but the noise of the engine, water, wind may prevent you from hearing detonation. This would be bad, so you probably shouldn't do it this way.<br /><br />I would concentrate on making the timing tab legible timing it with a timing light.

 

[Cut n' Jump]

Re: Timing w/ vacum gauge

If you really want to hear detonation take a long hardwood broomstick or something like that against the block and listen to the end of it. Of course you would need glassy water for that. Most parts stores or tool stores have a ready-made 'mechanics stethoscope' also. Let the motor idle and get a baseline sound. The clattering will come when someone else opens the throttle at once so DONT FALL IN THE BELTS! Usually spark knock comes in at higher rpm's under heavy load. Once cruising it may go away.