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minimember Samba Member
Joined: March 14, 2013 Posts: 119 Location: cupertino
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Posted: Thu Aug 14, 2014 11:51 am Post subject: valve events queston |
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I recently rebuilt my engine and now fear that the cam and crank may have rotated while putting the case halves together.
To verify this without taking apart the engine I assume that I need to know where each of the valve events should be when the #1 cylinder is at TDC.
Right now when I have the #1 cylinder @ TDC my current valve events are as follows:
#1 intake closed - Exhaust closed
#2 intake open - Exhaust starting to close
#3 intake starting to close - Exhaust closed
#4 intake closed -exhaust closed
Is it safe to assume that #3 should have an open exhaust and intake at TDC for #1? |
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telford dorr Samba Member
Joined: March 11, 2009 Posts: 3551 Location: San Diego (Encinitas)
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Posted: Thu Aug 14, 2014 12:00 pm Post subject: |
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As the firing order is: 1,4,3,2
#1 is at TDC on the compression stroke; intake closed, exhaust closed
#2 is at BDC on the power stroke; intake closed, exhaust opening
#3 is at TDC on the exhaust stroke; intake opening, exhaust closing
#4 is at BDC in the intake stroke; intake closing, exhaust closed _________________ '71 panel, now with FI
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busdaddy Samba Member
Joined: February 12, 2004 Posts: 51120 Location: Surrey B.C. Canada, but thinking of Ukraine
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Posted: Thu Aug 14, 2014 12:15 pm Post subject: Re: valve events queston |
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minimember wrote: |
fear that the cam and crank may have rotated while putting the case halves together. |
That's not an issue unless the cam fell out and wasn't reindexed on the crank gear when it went back in, I like to turn it alot as I'm torquing to confirm nothing's pinched.
The cam events won't help much as they never change (lobes can't move around on the cam), thier relation to crank TDC is what matters and without some precision measuring equipment you'll never know, eyeballing won't do. Pull the oil pump or get in there with a snake camera and confirm the dots line up when their teeth mesh.
If it's TDC for the distributor you are after put your finger in #1 hole and turn the engine until you feel compression, stop when the pulley says 0. Put the #1 spark plug wire in whatever disributor cap hole the rotor is pointing at and arrange the rest of the wires according to that. _________________ Rust NEVER sleeps and stock never goes out of style.
Please don't PM technical questions, ask your problem in public so everyone can play along. If you think it's too stupid post it here
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Слава Україні! |
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Wildthings Samba Member
Joined: March 13, 2005 Posts: 50334
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Posted: Thu Aug 14, 2014 12:35 pm Post subject: |
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I don't remember what engine you have, but if a type 4 remember that the timing mark doesn't line up with the split in the case. Most cams are going to have noticeable overlap at the top of the exhaust stroke. |
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minimember Samba Member
Joined: March 14, 2013 Posts: 119 Location: cupertino
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Posted: Fri Aug 15, 2014 9:47 am Post subject: |
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Thinking about it, it does seem rather unlikely that the teeth rotated while putting the cases together but I would love to be able to check if not just for piece of mind.
If I were to get a snake camera, what what would be my point of entry to confirm that the 3 dots are in alignment? Doesn't seem like there would be much space to much of anything at the point the dots intersect.
I have a 70 type 2 engine, with a stock 69mm cam. The book I used to rebuild it mentioned that when I'm at TDC for #1, that #3 should be at overlap. which I am definitely not at.
So confused, have done plenty of valve adjustments in the past, but something about this has my brain in knots. |
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busdaddy Samba Member
Joined: February 12, 2004 Posts: 51120 Location: Surrey B.C. Canada, but thinking of Ukraine
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Posted: Fri Aug 15, 2014 10:02 am Post subject: |
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I'll have to look at one that's apart but I'll bet you could go in through the fuel pump hole, my scope has a 90 degree mirror on the end that does close up stuff like that well, I don't know if those "look inside the wall" cameras that you can rent from Home depot can get up that close. _________________ Rust NEVER sleeps and stock never goes out of style.
Please don't PM technical questions, ask your problem in public so everyone can play along. If you think it's too stupid post it here
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vincev Samba Member
Joined: May 10, 2004 Posts: 84 Location: washington
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Posted: Sat Aug 16, 2014 8:29 pm Post subject: |
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Cranks and cams are intended to rotate so no problem there. If you think they are out of time with each other then you will have to split the case to know for sure or just run it. |
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williamM Samba Member
Joined: August 07, 2008 Posts: 4333 Location: southwest Arizona
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Posted: Sat Aug 16, 2014 9:04 pm Post subject: |
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Simple test is put fingers on #3 valves and rock the motor thru #1 tdc. Its called the rock point. and those valves must move as #1 TDC comes across- Otherwise split the case.
Does your engine have stock rivited cam or some after market, "adjust -a - cam" front gear?
As they say "Well- that thars your problem - right thar " _________________ some days I get up and just sit and think. Some days I just sit.
opinion untempered by fact is ignorance.
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minimember Samba Member
Joined: March 14, 2013 Posts: 119 Location: cupertino
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Posted: Sat Aug 16, 2014 9:09 pm Post subject: |
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I thought for sure the dots were aligned and didn't shift when put the halves together, but the valves just seem funky. The events don't seem to make sense. Perhaps I set them in reverse, but I tried rotating the plugs 180 and still no luck. All that I get when I try to start the car is an occasional backfire. Obviously pulling it back apart would tell me for sure but can't I check to see if the cam and crank our out of sync by using the specs of the cam lobes (inlet opens 7.5 deg BTCD, closes 37 deg ABDC, exh opens 44.5 deg BBDC, closes 4 deg ATDC) and the degrees on my pulley to verify?
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Wildthings Samba Member
Joined: March 13, 2005 Posts: 50334
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Posted: Sun Aug 17, 2014 4:55 am Post subject: |
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Looks like you only have about 11* of overlap at TDC exhaust, but it is overlap. You should be able to find the point this overlap is occurring. If anywhere besides TDC exhaust you know you have a cam timing problem. |
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williamM Samba Member
Joined: August 07, 2008 Posts: 4333 Location: southwest Arizona
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Posted: Sun Aug 17, 2014 11:06 am Post subject: |
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Did you static time the engine to 7.5 degrees? with a trouble light? and found TDC with finger over #1 SP hole and did rock point show up on #3 rockers and your ig rotor points at #1 and ig wires go 1432- or as I do it backwards to 1234?
Did you leave the pistons out?
coil wired up correctly?
battery hooked up correctly?
Should be able to solve this in an hour.- so go take a nap and try again. _________________ some days I get up and just sit and think. Some days I just sit.
opinion untempered by fact is ignorance.
Don't step in any! |
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williamM Samba Member
Joined: August 07, 2008 Posts: 4333 Location: southwest Arizona
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Posted: Sun Aug 17, 2014 11:09 am Post subject: Re: valve events queston |
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minimember wrote: |
I recently rebuilt my engine and now fear that the cam and crank may have rotated while putting the case halves together.
To verify this without taking apart the engine I assume that I need to know where each of the valve events should be when the #1 cylinder is at TDC.
Right now when I have the #1 cylinder @ TDC my current valve events are as follows:
#1 intake closed - Exhaust closed
#2 intake open - Exhaust starting to close
#3 intake starting to close - Exhaust closed
#4 intake closed -exhaust closed
Is it safe to assume that #3 should have an open exhaust and intake at TDC for #1? |
To answer the last question- yes- _________________ some days I get up and just sit and think. Some days I just sit.
opinion untempered by fact is ignorance.
Don't step in any! |
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