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Old 02-07-2014, 05:44 PM   #1
2pot
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Default Timing issues and an 83mm MPS crank

Any advice with this? Currently on the engine stand. Thought of 109 degrees, as a good starting point?
It's like the verniers/adjustable cam pulleys don't have enough adjustment. Can get to 110 on the exhausts and 111 on the inlets.

v4 heads - shimless conversion using eg33 exhaust buckets.
ej20 cdb
83mm MPS crank
Auto
92/93 ron
8.65cr
Cams



Any pointers? Does an 83mm crank have that much of an effect on cam timing?
What about using the LIC eccentric idlers as well?
Or a different centreline?
Your thoughts.
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Old 02-07-2014, 08:06 PM   #2
2Fast4U1DAY
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Quote:
Originally Posted by 2pot View Post
Any advice with this? Currently on the engine stand. Thought of 109 degrees, as a good starting point?
It's like the verniers/adjustable cam pulleys don't have enough adjustment. Can get to 110 on the exhausts and 111 on the inlets.

v4 heads - shimless conversion using eg33 exhaust buckets.
ej20 cdb
83mm MPS crank
Auto
92/93 ron
8.65cr
Cams

Any pointers? Does an 83mm crank have that much of an effect on cam timing?
What about using the LIC eccentric idlers as well?
Or a different centreline?
Your thoughts.
Contact DOM at MPS. Hes pretty thorough so im surprized he didnt give you special instructions if changes need be made
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Old 02-07-2014, 11:22 PM   #3
Paul
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^+2

your putting a 83mm crank in a 2.0l??
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Old 02-08-2014, 09:37 AM   #4
2pot
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Originally Posted by Paul View Post
^+2

your putting a 83mm crank in a 2.0l??
Small bore + long stroke = decreased flame travel distance, reduced detonation. Increased mechanical leverage to get the torque convertor moving. That's the theory, anyway.
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Old 02-08-2014, 09:45 AM   #5
2pot
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Originally Posted by 2Fast4U1DAY View Post
Contact DOM at MPS. Hes pretty thorough so im surprized he didnt give you special instructions if changes need be made
Perhaps he, like I, didn't foresee an issue.
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Old 02-08-2014, 01:21 PM   #6
kellygnsd
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I'm don't fully understand how a 83 mm crank would effect cam timing. Can you explain why you believe the crank is the culprit as opposed to other machine work or slop in the cam gear dowel pin.
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Old 02-09-2014, 06:43 AM   #7
2pot
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Originally Posted by kellygnsd View Post
I'm don't fully understand how a 83 mm crank would effect cam timing. Can you explain why you believe the crank is the culprit as opposed to other machine work or slop in the cam gear dowel pin.
Nor do I. May, or may not, have anything to do with it. Could just be a coincidence, but I've never seen this issue before.
I've now ordered some lic idlers, as I've used those before. Just seems overkill, to use verniers and eccentric idlers. When, I would have assumed, the verniers should have done the job.
Used BC I-beam rods 5.141" with 625 bolts and a 30.7 thou gasket, to get a 37.4 thou quench.
Open to any ideas?
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Old 02-10-2014, 02:30 AM   #8
2pot
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Originally Posted by kellygnsd View Post
I'm don't fully understand how a 83 mm crank would effect cam timing. Can you explain why you believe the crank is the culprit as opposed to other machine work or slop in the cam gear dowel pin.
How about this:
The 83mm crank alters the ratio of piston movement to cam movement.
The verniers were never designed to deal with that particular ratio.
So they can't split the 7 degrees, each tooth makes.

Anyone, now, care to suggest a centerline, given my set up?
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Old 02-10-2014, 03:19 AM   #9
kellygnsd
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The rod journals are 180 degrees apart and the added stroke is compensated with rod length and/or piston design. The only thing that should effect cam timing in relation to the crank would be changes in deck height due to decking the block and or heads, assuming the rod journals are all in line and the engine is timed correctly.

TDC is TDC whether its a 75mm stroke or a 83mm stroke. Did you just index cylinder #1 or did you verify the cam opening angles on all 4 cylinders to see if the centerlines are all shifted by the same amount?
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Old 02-10-2014, 03:25 AM   #10
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Quote:
Originally Posted by kellygnsd View Post
The rod journals are 180 degrees apart and the added stroke is compensated with rod length and/or piston design. The only thing that should effect cam timing in relation to the crank would be changes in deck height due to decking the block and or heads, assuming the rod journals are all in line and the engine is timed correctly.

TDC is TDC whether its a 75mm stroke or a 83mm stroke. Did you just index cylinder #1 or did you verify the cam opening angles on all 4 cylinders to see if the centerlines are all shifted by the same amount?
EDIT: Did you use a piston stop to verify TDC?
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Old 02-10-2014, 04:52 AM   #11
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Quote:
Originally Posted by kellygnsd View Post
The rod journals are 180 degrees apart and the added stroke is compensated with rod length and/or piston design. The only thing that should effect cam timing in relation to the crank would be changes in deck height due to decking the block and or heads, assuming the rod journals are all in line and the engine is timed correctly.

TDC is TDC whether its a 75mm stroke or a 83mm stroke. Did you just index cylinder #1 or did you verify the cam opening angles on all 4 cylinders to see if the centerlines are all shifted by the same amount?
When degreeing the cams, the piston travel to cam rotation ratio is different, whether it's 75/79/81/83. A some point, it must be outside the scope of the verniers. Unless they were designed to accommodate 109 degrees, with all possible crank to cam ratios in mind.
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Old 02-10-2014, 01:35 PM   #12
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Stroke has no effect on cam timing. Cam timing is done in relation to TDC and a given cam lobe center line offset (angle at a pre-determined lift point). If the block and or heads have had a decent amount removed that might be causing what you are fighting. Or if the key way was machined slightly off on the crank, or the cams dowel pin is slightly off that can also cause issues. If the issue is due to machining of the block I would adjust the belt tooth spacing so that you can achieve the proper cam timing while using the adjustable gears. If it turns out to be the crank key way then I would request a replacement crank from the supplier. Either way any good supplier can walk you through the process of determining what is going on and what the next step should be.
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Old 02-10-2014, 02:33 PM   #13
fastblueufo
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Use a degree wheel and make sure the marking on the crank for tdc is correct. If not then renotch the crank. Then determine if you still have issues. Tdc is tdc and bdc is bdc no matter what the stroke. Your still only dealing with 360* rotation. Check cam pulley size. Maybe they are junk.
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Old 02-11-2014, 09:31 AM   #14
2pot
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Originally Posted by gfx2043 View Post
Stroke has no effect on cam timing. Cam timing is done in relation to TDC and a given cam lobe center line offset (angle at a pre-determined lift point). If the block and or heads have had a decent amount removed that might be causing what you are fighting. Or if the key way was machined slightly off on the crank, or the cams dowel pin is slightly off that can also cause issues. If the issue is due to machining of the block I would adjust the belt tooth spacing so that you can achieve the proper cam timing while using the adjustable gears. If it turns out to be the crank key way then I would request a replacement crank from the supplier. Either way any good supplier can walk you through the process of determining what is going on and what the next step should be.
Thanks for the input. I tried one tooth advanced and one tooth retarded, and was further away.
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Old 02-11-2014, 09:32 AM   #15
2pot
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Originally Posted by fastblueufo View Post
Use a degree wheel and make sure the marking on the crank for tdc is correct. If not then renotch the crank. Then determine if you still have issues. Tdc is tdc and bdc is bdc no matter what the stroke. Your still only dealing with 360* rotation. Check cam pulley size. Maybe they are junk.
Once again, thanks for the input. Tried different adjustable pulleys and they were worse.
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Old 02-11-2014, 11:33 AM   #16
fastblueufo
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Quote:
Originally Posted by 2pot View Post
Once again, thanks for the input. Tried different adjustable pulleys and they were worse.
Did you degree the crank to see if it was marked correctly? Either the crank tdc marking is wrong on the crank or you had your heads and block decked alot. Check that your timing belt isnt stretched.

The first thing I would start with is checking the tdc marking on the crank by degreeing the crank. Then just go down the line of things that can cause your issue.
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Old 02-12-2014, 11:31 AM   #17
2pot
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Originally Posted by fastblueufo View Post
Did you degree the crank to see if it was marked correctly? Either the crank tdc marking is wrong on the crank or you had your heads and block decked alot. Check that your timing belt isnt stretched.

The first thing I would start with is checking the tdc marking on the crank by degreeing the crank. Then just go down the line of things that can cause your issue.
Crank is fine. New kevlar belt. Neither the block or heads have been skimmed other, than a clean up.

Interestingly the valves are clear in the piston pockets between 92 and 132 degrees!
I'm still of the mind that it's simply a lack of adjustability in the original, 75mm designed, v3/4 verniers.

Still awaiting the LIC idlers.

In the meantime, what centerline, given my set-up? Is it worth going to 112 degrees as it's auto.
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Old 02-13-2014, 12:57 PM   #18
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This might sound completely stupid but are you sure the cams are in the heads correctly and are not mixed up?
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Old 02-22-2014, 11:41 AM   #19
2pot
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Lic eccentric idlers solved the issue:
http://www.licmotorsports.com/produc...sti_lic-061505

All cams now within 109 - 109.5 deg.

Anyone like to suggest an optimum centerline for an auto? Would it be be significantly different from a manual?
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