The Triumph Dolomite Club - Discussion Forum

Hi back again........

Latest problem with my engine build.

A kind club member suggested putting this question to the forum,

I have fitted a brand new old stock Kent fast road cam KCDMS1. I have set valve clearances tighter than suggested at .20mm ( approx 8 thou ) or slightly tighter.

Attached the code on the cam plus data sheet that was in the box.

The question, do I or don't I need a vernier cam pulley?

The timing marks line up exactly, the head has be skimmed lightly at around 3 thou.

Please can anyone who's been there - done it advise.

Thanks in advance to all that can spare some time to advise me what I need to do.

Chris.

I thought another kind clubmember did answer your questions about this already by pm.

The best for you is to have a poll do need or don't need. Then you can choose.

Jeroen.

If you get a degree wheel, you will find out if you need a vernier or not. You need to aim for your 108 degrees number. If all marks line up and its 108 ATDC then no need to adjust. If you need to adjust lets say by 2 degrees you could also take the cam sprocket to a machinist and have 2 new holes drilled at 90 PLUS or MINUS the degrees you want to change it by. That way you will have the correct timing without the need for a vernier pulley. If you dont understand the timing (no shame there) then maybe get someone to time it up correctly with a degree wheel on the crank and dial gauge on the cam and verify how close it really is. If its new to you a bit of google searching on how to time a camshaft will pay dividends. Most likely US sites will give you the answer.
HTH

Tony

tony g wrote: ↑Tue May 23, 2017 10:26 pm If you get a degree wheel, you will find out if you need a vernier or not. You need to aim for your 108 degrees number. If all marks line up and its 108 ATDC then no need to adjust. If you need to adjust lets say by 2 degrees you could also take the cam sprocket to a machinist and have 2 new holes drilled at 90 PLUS or MINUS the degrees you want to change it by. That way you will have the correct timing without the need for a vernier pulley. If you dont understand the timing (no shame there) then maybe get someone to time it up correctly with a degree wheel on the crank and dial gauge on the cam and verify how close it really is. If its new to you a bit of google searching on how to time a camshaft will pay dividends. Most likely US sites will give you the answer.
HTH

Tony

Thanks Tony,

Very helpful, I will order up a degree wheel and carry out checks.
I have just found on a Kent cams data sheet ( googled ) they list a power pulley for use with this cam, so a hint I guess. I'll post the readings when I get them done.
Thanks again.

Now that you have the cam identified you can use the figures in the data sheet. I would advise against having the exhaust valve clearances
tight because the valves will be open slightly longer exposing seats and valve rim to hot gas for a tad longer. It might not seem much, but you really want maximum time for the valve and seat to be in contact and cool down, while allowing enough time for the exhaust gas to get out.

I presume by now your head is back on and torqued down, so its a tad harder to check the timing figures on the cam pulley are correct. They are usually pretty accurate, but its worth a check if you have a dial gauge.

Then you can put on your degree wheel and look at the inlet valve timing. You then have the options described above....luck out and you can use the marks you have, but I suspect you will be a few degrees out and need a change. Either get a new cam sprocket and have it drilled accordingly or try and get an adjustable one.

When I did mine some 25 odd years ago it made a massive difference to the power....about 30 bhp! The adjustable wheel makes the job MUCH easier.

Jonners

I will keep it as simple as possible and for a sprint only.

Before any timing attemps you have to obtain a timing wheel. Most of the time these plastic things are supplied with a camshaft but if not for a few pounds you can buy one. The pointers and carves in the original pulley are only to have an indication of where your ignition is about.

The timing wheel can be stuck on the pulley with some dual side adhesive tape.
The cilinders and valves what are talked about are all cylinder one.

All degrees talked about are crankshaft degrees.

Make yourself a pointer of a a piece of wire that you attach somewhere on the engine and runs closely around the timing wheel so you can actually see when the crankshaft is turned one degree.

To determine the exact tdc you have to use a dail gauge on your piston. Most likely you will need an extension to go throught the sparkplughole to reach the piston.
When the piston is exactly on top you can turn the crankshaft about 3-4 degrees without movement of the piston. That’s why you have to take a pen and paper to write some. You set the piston for example on 0,25mm before tdc and note your degrees shown on the disc at your pointer. Then rotate to tdc and set the piston on the same height after tdc. Note the degrees. The middle of these two figures is the exact tdc. Set the crankshaft on tdc and have the disc/pointer also on exact tdc.

Now rotate the crankshaft about 90 degrees towards 108 degrees after tdc so no valves can hit the pistons for the next step.

Timing the camshaft goes the exact same way. At the sprint you have to set the inlet valve on max lift. The same as with the piston there are a few degrees you can turn but the valve doesn’t move. You can make a pointer again, have a sort of mm divided strip on the sprocket and the dail gauge on the valve bucket. Note the two figures, middle and you have your exact max lift. As this is not about degrees but max lift any scale you can use to determine the max position but the more distance from the camshaft the more accurate the measurement. Best is some paper measuring tape around the camsprocket.

Now set the crankshaft to 108 degrees after tdc. Now you have both in the right postition. Does the chain fit exact you do not need more to do than fit and assemble the engine. Most likely the chain doesn’t fit and then you can use a vernier sprocket.

What you also can do is to have the holes in your original sprocket oval so you can slighlty rotate the sprocket on the camshaft. When the chain does fit you can tighten and drill two new holes in one go through the sprocket and camshaft to have two extra bolts or two dowels.

The original little bolts do shear so it is strongly advised to fit an extra set of bolts.

But before permanent fixing, turn over the engine by hand and check again. Slack of the chain should not be underestimated.
Two or three degrees off does make a lot of difference in running and the bhpeees.

In the drawing you can see the opening time of the inlet valve of this particular kent cam. I didn’t draw the exhaust because that is not needed for setting the timing so keeping it simple.

36/72, duration of 288 degrees and timing set to 108 degrees.

Means:

36 degrees before tdc the inlet valve starts to open when the valve play is correct. 72 degrees after bdc the inlet valve is closed when the valve play is correct.

Duration is the total opening of the valve in crankshaft degrees. 36 + 180 + 72 = 288 in total.

Max lift is in the middle at 288/2= 144 degrees after opening.
36 degrees were already to tdc so 108 left after tdc to max lift.

That’s all.

Jeroen

A big thanks to all you guys for taking time to help and advise, so very much appreciated.

Chris.

Carried out the timing check today, full lift shows at 113 degrees, as opposed to the required 108.
So the search begins for a good quality vernier!

I am just about to time a cam in (Newman STR91) and I have put a couple of screws in the lathe and turned the thread off down near the head of the screw, which means the cam wheel can move without slotting the cam sprocket. When 108 ATDC (or 106) is achieved I will drill through the camwheel to spot the cam so as to accurately position the existing sprocket and then slot the holes to suit leaving the cam with four screws to hold it I will picture it all and then try to load them up on here.

Worth saving this one I think for future cam players.

Thanks Jeroen, that is the best step by step explanation I have seen.

This is how TJ did mine....just to illustrate a point....

shaunroche wrote: ↑Fri Nov 10, 2017 11:52 pm This is how TJ did mine....just to illustrate a point....

Could we have some bigger pictures, they are a bit hard to make out?