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Author Topic:   SBC engine timing problem
rickbraley
Dirt Full Roller

Total posts: 58
posted April 11, 2005 03:42 PM  
Has anyone experienced their engine timing retarding as engine rpms move from idle to somewhere around 3000 rpm?

I have an MSD billet distributor with the advance locked. I set my timing to 36 degrees at around 1500 rpms then I can watch the timing retard almost 10 degrees as the engine rpm rises.

I have verified the cam button to timing chain cover clearance to be no more than .025 and my distributor gear appears to be mating with the camshaft adequately.

Any ideas?? I should not see the timing fluctuate at all with the distributor locked correct? Any insights would be appreciated.

ctfarm
Dirt Freak

Total posts: 206
posted April 11, 2005 04:09 PM  
A bad ignition module or ign.box will do this.It will retard the timing electronically.I've had this happen on several of the stock type modules.


dan ferry
Dirt Maniac

Total posts: 183
posted April 11, 2005 06:23 PM  
im having the same problem i just broke my engine in this evening and timing is retarding as rpm increases and my distributor is welded and wasnt having this in the other engine i set cam backlash to.005 roughly as instructions on button say, i noticed cover flexing as i hit throttle cam is pushing it out some but seems to go back in if you hold throttle open timing is steady just retards as u raise rpm i set it at 35 at 3000 rpm and dropped to idle at 1500 rpm and timing was 40 thanks for any info maybe stock peace sign cover isnt strong enough? but cam only moves on quick punch and moves back if hold at rpm maybe module makes sense

rickbraley
Dirt Full Roller

Total posts: 58
posted April 11, 2005 08:39 PM  
dan, I think we are having the same problem. The symptoms you describe are exactly the same as I am having. You can actually see the cover flexing? I tried to watch mine but I can't see anything. I wonder how much the cam would have to move to effect the timing 5 - 10 degrees?

For reference I am running a MSD 6AL with the MSD Blaster coil. Distributor is the MSD 8550 (guessing on the number for the dist, SBC billet dist with no adjustable collar) with the advance locked. I have a roller cam with the roller cam button. I am also using a stock cover with some slight modifications to get the clearance right.

Is there an aftermarket cover that is more rigid?

I have a second MSD 6AL that I will try and see if that makes any difference. I had the module tested by MSD last year so it should be good. If it is the module I would think that would resolve it. Seems unlikely that two modules would have the same problem.

Anyone else have anything similar or figure out a resolution to a similar problem?

sdhnc29
Dirt Forum Champ
Total posts: 934
posted April 11, 2005 09:15 PM  

The timing cover flexing forward is your problem. You need a positive stop outside of the cover to prevent this problem. Many aluminum water pump's have this provision built into them. If you do not have this style pump, then you will need to fabricate a positive stop on the back of your existing pump.

Steve

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Hendren Racing Engines
Rutherfordton , NC
(828)286-0780
http://www.hendrensracingengines.com

rickbraley
Dirt Full Roller

Total posts: 58
posted April 12, 2005 06:15 AM  
Steve, thanks for your feedback!

Do you have an example or some more info on exactly how this positive stop should be constructed? Can I assume it is simply a piece of metal that will fill the gap between the back of the pump and the cover?

Also, did you ever evaluate that racepumps.com fuel pump? Ironically my Edelbrock pump appears to have died and I need to get something ASAP.

Thanks.

dan ferry
Dirt Maniac

Total posts: 183
posted April 12, 2005 06:02 PM  
thanks steve i was checking the walking and timing and distrubutor wear closer tonight and thats is it. cam pushes out at idle and in at higher rpm i pushed on cover with a bar while idling and could hear engine tone change kind of hard and dangerous to do and watch timing. maybe i cold weld a nut or something to back cover of pump, i'm assuming i'll have to back of rockers to allow to make sure cam is back all the way and see what'll fit thanks again

dan ferry
Dirt Maniac

Total posts: 183
posted April 12, 2005 06:06 PM  
rick you can get a cloyes aftermarket cover thats definately more rigid, aluminum.

sdhnc29
Dirt Forum Champ
Total posts: 934
posted April 12, 2005 07:33 PM  
Yes guy's, you can make a plate that bolt's to the back cover of the water pump. Then put a hole through it, run a bolt up against the timing cover, and this will help a lot. Ultimately it would be best to buy a water pump that has this provision built into it, or use the Cloyes cover as was suggested.

Steve

------------------
Hendren Racing Engines
Rutherfordton , NC
(828)286-0780
http://www.hendrensracingengines.com

sdhnc29
Dirt Forum Champ
Total posts: 934
posted April 12, 2005 08:16 PM  
rickbraley

I'm going to run this new fuel pump this weekend. So I'll post my opinion on it after that. If I have time before Friday, I'll run the car on the chassis dyno as well. At any rate, I'll let you all know.
Steve

------------------
Hendren Racing Engines
Rutherfordton , NC
(828)286-0780
http://www.hendrensracingengines.com

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