9 replies to this topic

[buddha01]

hi all
i want to put a 286 cam in my 1275 a plus but was told i would need an offset timing keyway? could anyone shed some light on this and as to
what keyway i would need or how to find out? would appreciate any info. thanks

[AndyMiniMad.]

Speak to the cam suplier. They should be able to provide the optimum cam timing. You will also need to fit an adjustable timing chain and use a dial test indicator and the cam timing wheel if you want to get it spot on. The offset woodruf key you mention fits in the slot at the end of the cam and then "offsets" the timing gear to the correct setting. if you use this method and have the correct key then you probobly wont need to bother with the dial test indicator or adjustable gear.
I prefer to use duplex vernier adjustable stuff as the cam timing can be set very acurately.

Have you done any other work to this 1275 engine? the cam wont work at its best if the head has not been worked on.

[Cooperman]

The 286 is a race/rally cam and as such it is not really very good for a road-going Mini which is not going to be used in serious competition. It also needs a well gas-flowed head, twin 1.5" SU carbs (or something equally good), a good exhaust system, a lightened flywheel, etc. Without all this you'll just get all the disadvantages of the 286 with none of the advantages. also, with a 286 your engine should be capable of revving safely to about 6800 rpm and a final drive low enough to allow you to pull away without excessive clutch slipping in 1st.
With regard to timing, the ideal timing for a 286 is 106 degrees ATDC on inlets. To achieve this accurately you need to use either an offset woodruff key or a vernier cam drive sprocket. You measure using a DTI and crank protractor to measure the basic setting without any adjustment, then fit the offset key or rotate the vernier sprocket to remove any error. You may have to mneasure and re-set several times to get it absolutely right which is essential in a race engine. Of course, you can simply set the cam using the standard dot-to-dot method and it will run, but if fitting a 286 you won't get best power and it could run even worse at low revs that it will do when timed in accurately.
The 286 is a really lumpy cam and as you will be using lots of revs all the time to keep it on-the-cam expect to rebuild the engine more often.

[buddha01]

thanks for your help guys. as for other mods i have a weber dcoe 40 an lcb with single box exhaust system electronic ignition with some sort of fast road dizzy
and have a mildly moded head vizard style. im hoping it will work well if i spend time setting it up properly.

[dklawson]

No comment on the cam selection and or other go-fast bits. But I do have comments on the offset keys.

You have three choices. The cheapest is to use stock timing pulleys and line them up using the dot-to-dot method described in the manual. This however will not set your cam to the grinder's specified optimum angle. To set this angle accurately you use EITHER an offset key with standard timing pulleys, OR you use the vernier adjustable timing pulleys. You do not choose the offset key based on the cam maker's specs, you choose the key based on careful measurements. Setting the cam angle using any method other than dot-to-dot dictates that you MUST have a dial indicator and degree wheel.

There have been several threads here (with external links to tech articles) that describe how to degree a cam. Please try the search feature to find a few of these threads and read up on the process. If you can't find those old threads, post back and we'll help locate a few.

Regardless, the method of setting the cam angle is to measure the cam angle as installed before any adjustments/corrections are made (requires dial indicator and degree wheel) then determine how many degrees out the cam is from ideal. Knowing the angular error, you select an offset key to provide the correction OR you use the vernier pulleys to create the correction. Most people make an additional 1-2 degree offset to the cam timing to compensate for timing chain stretch that will occur during the break in period of the new timing chain.

[bmcecosse]

There is no way of knowing exactly what will be the 'best' timing for a cam like that in YOUR engine. What works well in one engine may be hopeless in yours. I have used the 544 cam very successfully in a number of engines - without the hassle of fiddling with offset keys etc. I just set it dot to dot with a duplex chain. Sure -I may have been 1 bhp down on the optimum possible, but that optimum may not have been at 106 degrees anyway,or whatever other magic number is quoted. And in any case - if they KNOW it's always best at 106 degrees - why don't they grind the cam so it will install at 106 degrees!!?? The only way to find out for sure in YOUR engine is to try it at one setting ( ie dot to dot) - then adjust it slightly one way and try again, then adjust etc etc until you feel it is best for you. Tedious in the extreme... As suggested earlier - this cam really needs a strengthened/balanced engine and a good head with the large inlet valves - and your 40 DCOE is too small for the job. It's only roughly = twin 1 1/4" SUs - so you need twin 1 1/2 SUs - or a single HIF 44 (best bet I think) or a Weber 45 DCOE if you have the facilities and patience to set it up properly.......

[dklawson]

if they KNOW it's always best at 106 degrees - why don't they grind the cam so it will install at 106 degrees!!??

The cam will be as accurate as they can make it and close to correct when dot-to-dot is followed with new, ideal components. However, the answer to your question is "tolerances".

There are MANY components that add into the tolerance stack up. You have the crank and its keyway (1 angular position), the keyways in both timing pulleys (2 angular tolerances), the pitch of the timing chain (God knows how you factor that in... one tolerance per link or....). Though I have not personally seen the dot-to-dot method off by more than a few degrees, I have seen one or two people post that they have found the dot-to-dot method out by as much as 6 degrees.

Setting the cam angle factors out ALL of these manufacturing tolerances to create the optimum lift when/where bench testing has shown the cam to perform best in testing.

[AndyMiniMad.]

I set my cam RE 13 OT at 104 deg based on what the manufacturer said was the optimum. As it turned out dot to dot was virtualy bang on and only the smallest if adjustments to the vernier gear was required. So have I got this wrong then mr dklawson. should I not have set it to the makers suggested settings. Sorry if im being a bit thick here. But im a tad confused now.

Oh and sorry to the OP if my previous post was in any way missleading. Of course you would use either the vernier gear or the offset keys. Not both..

[Cooperman]

When I've set up using the dot-to-dot method I've had the timing come up from exactly correct to as much as 9 degrees retarded and 6 degrees advanced. I put this down to manufacturing tolerances in the usually after-market duplex sprockets rather than the cam itself.
Maybe I'm overly fussy, but I time every cam in accurately on every engine I build at 2 degreees advanced from manufacturer's recommendation to allow for the high initial chain stretch which settles down after a few thousand miles.
It's not really an onerous job and when it is absolutely accurate it's very satisfying to have done the job right. I do believe it makes for a better engine. Time taken can be anything from 10 minutes to an hour. Just start with the baqsic standard dot-to-dot and measure that. The correct with offset key as necessary.

[dklawson]

I set my cam RE 13 OT at 104 deg based on what the manufacturer said was the optimum.
So have I got this wrong then mr dklawson.
should I not have set it to the makers suggested settings.

You have done nothing wrong. Roy mentioned the 106 degrees.... I never mentioned the specific angle because it can be different for different cam grinds.
All I suggested is what Cooperman said, a 1-2 degree increase in the cam angle (initially) so the cam will drift into "proper" time as the timing chain stretches. The spec provided by the manufacturer will not include that extra 1-2 degrees.