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sounds like you are getting there. its great to hear that is wasnt something internal.
just rebuilt runs bad
- Thread starter 6tfo
- Start date
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Thanks, but there is still a problem. With timing set at 18 BTDC i went for a test drive. When giving it gas the engine starts breaking down. I'd pull over and turn the Dist. about an 1/8 inch and the engine ran better. I did this a few times and it ran better each time. I stopped increasing because I was getting worried of damaging something. When I got back I measured initial timing and it was at 38 BTDC.
There's a couple more things in this string that I still haven't checked or done that I hope to do today and I have a pretty knowledgable friend coming over to take a look. If no luck after that I'll call my machinist and ask him to refer me to an ignition/tune up guru that he trust. From there the guru will either fix my ignition or tell my machinist he has a problem. That's my plan.
67Dart273
Well-Known Member
So, you are saying that it ran at 38 AS MEASURED AT IDLE????
This is really sounding more and more like either the timing marks are not right, or the cam is out with the crank.
With the timing advanced to run "good" as per your last test, what is the timing at high RPM?
And I have to say, at this point, a second pair of eyes sounds like a great thing to have.
This is really sounding more and more like either the timing marks are not right, or the cam is out with the crank.
With the timing advanced to run "good" as per your last test, what is the timing at high RPM?
And I have to say, at this point, a second pair of eyes sounds like a great thing to have.
High RPM timing is something I haven't checked since switching to the points system (that ones to tricky for me to do by myself). I'll check it when my buddy comes over this afternoon.
I'm also going to show him how I've verified the timing mark (about 5 times now with a stop) just to make sure I'm doing it right. We'll check everything. He's an AMC guy and knows his stuff, he's also an electronics engineer but we don't like to hold that against him.
kman521
Well-Known Member
I know you checked the cam timing with the number 6 in overlap but imho that cam is not installed properly.
By the time my buddy arrived I had the plugs out, dist. cap off, fan removed (to hand crank motor easier), and valve covers off. We checked TDC with the piston stop. The TDC mark on the balancer was spot on against zero on the timing chain cover. With the #1 piston at TDC on compression stroke I kept hand cranking the engine clockwise. At 180 ATDC the #1 exhaust valve started opening, and the same time the number 6 cylinder intake started opening. We turned the engine back to TDC compression stroke and added 12 degrees (12 BTDC). The rotor was pointing towards the first bolt on the intake drivers side and we lined the #1 distributor terminal accordingly. Put everything else back together and started the engine. After it warmed up we adjusted initial timing to 18 BTDC and went for a test drive. It did not run well, missing an no power when pushing down on the pedal. We stopped and readjusted initial timing to 35 BTDC. It ran tons better and I turned to my buddy for answers.
After talking about it we decided to try total timing. So we went back to 18 BTDC initial, increased RPM and at over 4K RPM set timing at 38 BTDC. This brought initial timing down to 12. We test drove and to my surprise it ran pretty good. There was still some miss firing and power loss upon acceleration but it wasn't terrible. We agreed that with a little tweaking it may run decent and if nothing else the timing setting as is shouldn't hurt anything. He thought maybe my high initial timing readings were due to my idle being up around 800 to 900 RPM and the Dist. mechanical advance being sensitive. He suggested not to worry about previous initial timing settings and focus on total timing and try and get it running good where it is now by tweaking.
Honestly, I'm still puzzled.
This thread has probably gone on for too long to be productive to others anymore. There is great advice here from the A body community which I truly appreciated. Thank you all. I'll either get it figured out, break something bad, or take a sledge hammer to it. Whatever the outcome I'll post it here.
Thanks again.
67Dart273
Well-Known Member
Something is seriously wrong. Here's the valve specs, just as an 'xample, on a 72 340, right out of the shop manual: (318 is left column of numbers, 340 middle, 360 far right.) Notice that exhaust opens WAY BEFORE Bottom Dead Center (BDC) or 180*
You should be able to get (or have!!) the exact timing specs for whatever cam is in the engine. MOST especially, if the crank is degreed or "timing taped" you should be able to walk it through a whole cycle of the no1 cylinder (Don't confuse yourself with others) and see where you stand.
You sure you are at 12 BTC, or 12 AFTER TDC?
I've been trying to get you to use total timing, until you get it sorted. ANY engine should run "fair" negating dist. advance curve, at around 35-40 in the context of this type engine.
ARE YOU sure you don't have a crappy wire or two, or bad plug?
I disagree the thread is "getting too long."
PLEASE keep us updated
kman521
Well-Known Member
That cam the exhaust valve should be opening 78 deg BDC so something is wrong.
Your cam specs are on this page.
http://www.performancetransparts.com/crs280hpp474camandlifters.aspx
Thanks guys. Both of you just posted some really great information and opened a new troubleshooting path for me.
I'm going to put a timing tape on the harmonic balancer and measure when each #1 valve opens and closes. This should really tell if the cam is installed correctly, shouldn't it?
Thanks so much.
I'm going to put a timing tape on the harmonic balancer and measure when each #1 valve opens and closes. This should really tell if the cam is installed correctly, shouldn't it?
Thanks so much.
kman521
Well-Known Member
That's right, just make sure you are watching when the valves just start to open. It might be hard to see when the valves are just closed. If you had a dial indicator to read when the valve moves it would be better but if you watch closely you should be able to get pretty close.
Did you ever get a better explanation why the original timing set wouldn't work?
No, I need to do that. I feel that I understand enough now to be able to follow the explanation. Thanks.
dilley340
Well-Known Member
I know you said that you had checked TDC and it was spot on, but I thought you also mentioned that the machine shop scribed a new timing mark. With that said, are you sure the machine shop installed the timing chain to the correct indexing dot? On my Mancini set, there were two dots. The actual timing dot was kinda hard to see. Please see the image below.
I know you said that you had checked TDC and it was spot on, but I thought you also mentioned that the machine shop scribed a new timing mark. With that said, are you sure the machine shop installed the timing chain to the correct indexing dot? On my Mancini set, there were two dots. The actual timing dot was kinda hard to see. Please see the image below.
Thanks Doug. The shop didn't use the Mancini chain set saying they had problems during the degreeing process. I plan to call them today for more details.
In your picture I see the dot you point to, is the other dot you're referring to right above the key slot?
dilley340
Well-Known Member
I originally used the dot just over the keyway. I had used that dot at first and couldn't get the cam degreed. I called Mancini and they said that the crank keyway should be located at the one-o'clock position and to look for the other dot.
Great info thanks, I can certainly see how it would be confusing. I'll find out if my machine shop did the same thing but instead of calling Mancini like you did they just ordered a chain they were familiar with.
72ScampTramp
Scamp Tramp
I guess I have to ask. I know several have touched on this being a timing/cam install issue. I guess while your chasing everything down and yes I know its more work but why not pull the timing cover and verify? Or maybe you did and I missed it?
Thanks, no I haven't removed the timing cover. Other than the valve covers, I'm trying not to go into the engine. If it ends up back in the machine shop I want to lessen the chance of any finger pointing i.e. the machinist saying "you had the timing cover off how do I know you didn't didn't change something".
It may not sound like it but I still trust the machine shop and if it ends up being a build problem I believe they will make good. At the same time I don't want to take any chances by opening the engine myself unless I absolutely have to.
I sent the machine shop the picture of the mancini timing chain set. I also tried unsuccessfully to call him last week. Here's his response:
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Hey Dan.
December 13 TH Verizon was supposed to set up high speed Internet in my business but instead they knocked out my phones for a whole week...sorry you couldn't get through. As far as the marks on your timing chain, your cam was degreed in according to the cam card. I can install your cam by degreeing it even if there were no marks on the gears at all.
I am in the middle of something that I have to focus on until about noon tomorrow. Give me a call sometime tomorrow afternoon when you get time and will talk.
Thanks
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So I'll call him tomorrow and see what he says. He's been in business for over 30 years. I hope I'm not a sucker but I still trust the guy. We'll see.
Thanks.
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Hey Dan.
December 13 TH Verizon was supposed to set up high speed Internet in my business but instead they knocked out my phones for a whole week...sorry you couldn't get through. As far as the marks on your timing chain, your cam was degreed in according to the cam card. I can install your cam by degreeing it even if there were no marks on the gears at all.
I am in the middle of something that I have to focus on until about noon tomorrow. Give me a call sometime tomorrow afternoon when you get time and will talk.
Thanks
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So I'll call him tomorrow and see what he says. He's been in business for over 30 years. I hope I'm not a sucker but I still trust the guy. We'll see.
Thanks.
After thinking more about it, I'm just wondering are those cam specs in crank or cam degrees. If I understand correctly 78 cam degrees would equal 156 crank degrees. My 180 out was an eyeball reading on the crank which would make 156 in the margin of error for eyeballing I'd think.
Beatnik
Well-Known Member
Man just read through this whole thing for the first time...I'm morbidly curious as to what the outcome is. There's GOT to be an answer...and it has to lay in the degree'ing of the cam and the timing chain issues.
Man you are a VERY patient man...I'd have gone cert. nuts a long time ago.
Just take solice in the fact that your trials/tribulations are going to help others SO much down the road w/ similar problems! Good luck
Man you are a VERY patient man...I'd have gone cert. nuts a long time ago.
Just take solice in the fact that your trials/tribulations are going to help others SO much down the road w/ similar problems! Good luck
Patience? In medical terms my condition is described as Cranium Anesthesia, or numbness of the brain.
Thanks for commenting your post gave me a laugh when one was needed.
kman521
Well-Known Member
Cam specs are in reference to crank degrees.
When you install a cam you degree it in with a degree wheel on the crank.
Beatnik
Well-Known Member
Glad I could help in a completely non-helpful kinda way...
Copy that. Thanks.
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