Cam timing on the Essex V6
Discussion
Hi Guys,
I have a Fast Road Cam in my 3.1 Essex V6. The engine is running, starts fine, fuel economy is a little high, but it pulls like a tractor at low revs but quickly seems to run out of guts when the revs get up to 4k+. Someone has suggested that the cam to crank timing might be out. Now according to the engine specs, the cam is 2 Deg advanced of TDC.
So my question is....with the engine in the car, how can I check where the cam is in relation to the crank to work out if it's right?
Thanks,
Wayne.
I have a Fast Road Cam in my 3.1 Essex V6. The engine is running, starts fine, fuel economy is a little high, but it pulls like a tractor at low revs but quickly seems to run out of guts when the revs get up to 4k+. Someone has suggested that the cam to crank timing might be out. Now according to the engine specs, the cam is 2 Deg advanced of TDC.
So my question is....with the engine in the car, how can I check where the cam is in relation to the crank to work out if it's right?
Thanks,
Wayne.
When you say timing, I am guessing at the distributor timing and you want to check cam timing.The real way to test this is possible with the engine in situ, but quite fiddly. You will have to attach a timing disc to the front pulley and determine TDC of the piston using a dial gauge down the spark plug hole of the number 1 piston. Set this at o deg with a wire pointer. The remove the rocker cover and put the DTI on the inlet rocker. turn the engine over with a spanner and see what maximum lift is.If it dwells on the top of the cam for a few degrees, it will be the middle value of the maximum lift and see the dial on the crank to see what it is. You will need cam data from the manufacturer to see if it is right.To change the cam timing is even more tricky,unless you have adjustable cam sprockets, although some V6's had gears and might need offsetting keyways.
Rather like someone asking for instructions on DIY brain surgery I tend to think that people asking how to time cams in means it's clear they don't have the equipment or knowledge to do so anyway and trying to explain it would be pointless. Just the fact that you think that a 270 degree cam means it reaches full lift 270 degrees after something tells me not to touch this one with a bargepole. Do some Googling, ask Piper or Kent for a cam catalogue which will explain this in detail or get an older brother or sister to help before you have someone's eye out but I doubt if anyone in here is going to try and explain cam timing from scratch to a non engineer given the length, detail and diagrams it would need to do so properly.
ok Dave, then explain to me from your vast knowledge, would the timing of the cam to the crank cause the engine to drop off it's power after 4000 revs?.
I'm just a guy trying to understand what / how / and why this might be happening.
Not saying I'm a genious and will try and fix it myself
I'm just a guy trying to understand what / how / and why this might be happening.
Not saying I'm a genious and will try and fix it myself
Yes it can but so can lots of other stuff... why do you think it's the cam timing and not anything else? Always make sure the ignition system is in full working order and correctly set up - timing correct, advance mechanism operating correctly, no weak spark at high revs - then the carburation, and the tappet adjustments. Once you're sure the "adjustables" - which are adjustable for a reason - are all fine, only then, if it still doesn't work, is it time to look at the "heavy stuff".
Two degrees isn't a lot, either, but then if it is out we don't know how much it's out by.
Sounds to me like your cam keeps the valves open for 270 degrees of crankshaft rotation, and should be set so that equal lift on inlet and exhaust valves is achieved 2 degrees before TDC. Assuming that it has the same symmetry as the vast majority of cams, it will then be achieving maximum lift on the inlet valve 88 degrees after TDC.
First thing to do is to find TDC on no. 1 of course... can be a bit tricky to find the top of the peak as it's a flat peak, not a sharp one... tends to be a case of rocking back and forth past TDC, noting where the piston begins to drop noticeably either side of TDC and zeroing in on a point half way between. Make your final approach to this point turning the engine forwards, and then make a scratch on the crank pulley aligned with a fixed marker at this point... gives you a chance to see how accurate the ignition-timing marks provided are
Then turn the engine forwards and find maximum lift on no. 1 inlet valve. Again it tends to be a case of finding the midpoint between the two points at which there's a noticeable fall; again make your final approach to this midpoint turning the engine forwards. Make another scratch on the crank pulley aligned with the fixed marker.
Using a flexible tape measure wrapped around the pulley measure the distance between the two scratches (the shorter way), and also the distance right the way round the pulley. Most pulleys, though not all, do have a parallel-sided section on them which makes this straightforward. If not you could cut a length of old fanbelt to fit once round the groove and then wrap insulating tape round it until you have a level surface to put the measuring tape on.
The cam timing is (360 * (distance between scratches) / (distance around whole pulley)) - 90.
Two degrees isn't a lot, either, but then if it is out we don't know how much it's out by.
Sounds to me like your cam keeps the valves open for 270 degrees of crankshaft rotation, and should be set so that equal lift on inlet and exhaust valves is achieved 2 degrees before TDC. Assuming that it has the same symmetry as the vast majority of cams, it will then be achieving maximum lift on the inlet valve 88 degrees after TDC.
First thing to do is to find TDC on no. 1 of course... can be a bit tricky to find the top of the peak as it's a flat peak, not a sharp one... tends to be a case of rocking back and forth past TDC, noting where the piston begins to drop noticeably either side of TDC and zeroing in on a point half way between. Make your final approach to this point turning the engine forwards, and then make a scratch on the crank pulley aligned with a fixed marker at this point... gives you a chance to see how accurate the ignition-timing marks provided are
Then turn the engine forwards and find maximum lift on no. 1 inlet valve. Again it tends to be a case of finding the midpoint between the two points at which there's a noticeable fall; again make your final approach to this midpoint turning the engine forwards. Make another scratch on the crank pulley aligned with the fixed marker.
Using a flexible tape measure wrapped around the pulley measure the distance between the two scratches (the shorter way), and also the distance right the way round the pulley. Most pulleys, though not all, do have a parallel-sided section on them which makes this straightforward. If not you could cut a length of old fanbelt to fit once round the groove and then wrap insulating tape round it until you have a level surface to put the measuring tape on.
The cam timing is (360 * (distance between scratches) / (distance around whole pulley)) - 90.
Pigeon said:
Sounds to me like your cam keeps the valves open for 270 degrees of crankshaft rotation, and should be set so that equal lift on inlet and exhaust valves is achieved 2 degrees before TDC. Assuming that it has the same symmetry as the vast majority of cams, it will then be achieving maximum lift on the inlet valve 88 degrees after TDC.
Not even remotely close. No cam ever made would be timed for full inlet lift at 88 degrees after TDC. Somewhere in the range 105 to 108 would be appropriate for an average fast road cam in a 2v engine but only the maker's specs will tell where this particular one should be timed.FWIW my recommended starting point for timing single cams in 2v engines is always 3 degrees advanced from the "straight up" position i.e. full inlet lift at 3 degrees less after TDC than the lobe centreline angle. So if the LCA is 109 degrees then full inlet lift would be set to 106 ATDC. Swings either side of that can then be made on the dyno but I rarely find my starting point to be far out.
My engine was built by Specialised Engines, bored to 3109cc, big valve heads and gas flowed, SEV2 cam ( but that means nothing, it's just their own name they give their fast road cam ) with a 38Dgas weber jetted to suit the engine. I must admit I'm still running with points and am looking to fit electronic ignition asap. Unfortunately their records for this engine were lost some time ago! They have all their engines on file back to 1970 except for 3 months missing right when mine was built 
I've spoken to them and they say the cam has full lift at 109 Deg. So that's in line with what Dave says.
It's obvious from you guys the cam timing is a job for an experienced guy, so once I get all the 'adjustables' sorted then I'll book it in with Ric Woods for a rolling road set up. By that time I'll have made the tubular headers and can fit the triple webers.
PS The engine has been timed up at a mechanics and the gases were checked and carb set up. Hence looking towards the cam timing.
I've spoken to them and they say the cam has full lift at 109 Deg. So that's in line with what Dave says.
It's obvious from you guys the cam timing is a job for an experienced guy, so once I get all the 'adjustables' sorted then I'll book it in with Ric Woods for a rolling road set up. By that time I'll have made the tubular headers and can fit the triple webers.
PS The engine has been timed up at a mechanics and the gases were checked and carb set up. Hence looking towards the cam timing.
Edited by waylison on Tuesday 28th April 17:11
Pumaracing said:
Pigeon said:
Sounds to me like your cam keeps the valves open for 270 degrees of crankshaft rotation, and should be set so that equal lift on inlet and exhaust valves is achieved 2 degrees before TDC. Assuming that it has the same symmetry as the vast majority of cams, it will then be achieving maximum lift on the inlet valve 88 degrees after TDC.
Not even remotely close. No cam ever made would be timed for full inlet lift at 88 degrees after TDC. Somewhere in the range 105 to 108 would be appropriate for an average fast road cam in a 2v engine but only the maker's specs will tell where this particular one should be timed.FWIW my recommended starting point for timing single cams in 2v engines is always 3 degrees advanced from the "straight up" position i.e. full inlet lift at 3 degrees less after TDC than the lobe centreline angle. So if the LCA is 109 degrees then full inlet lift would be set to 106 ATDC. Swings either side of that can then be made on the dyno but I rarely find my starting point to be far out.
Gassing Station | Engines & Drivetrain | Top of Page | What's New | My Stuff