Help dialing in the timing...

I am still experiencing some issues with my new rebuild and I suspect it deals with timing. Jeff rebuilt my 25D dizzy and it looks great and I'm confident that it will perform well once I get it all sorted out. I suspect that I have a timing issue as a result of a newbie oversight.

On reassembly, I received some terrific advice particularly from Jeff, Jack and Hap. During parts inspection, it was determined that I had a never fired Kent 715 Fast Road cam. Hap wrote, "...your cam based on your spec appears to be a Kent 715, Valve lift .358" advertised duration of 286, center line of 106 degrees ( I recommend you advance it three degrees and time it at 103 degrees) and the valve lash on the 715 is .016" hot. This is a low lift cam, that has a fair amount of duration, it should be a torquey cam." That was later confirmed by paperwork and cam markings.

When I reassembled the timing gears, I followed the instructions from Dr. Doolin and placed the timing marks appropriately facing one another (for a stock cam). I continued with the r/r, set the valves, etc and the timing per Jeff at 14* static. It car starts well but it doesn't seem to have the torque and power that I think it should. When the car went into the garage for rebuild, it had low compression across the board, burning oil, and was just tired. I am not expecting to rip the rubber off the wheels, but apart from not burning oil, the engine just does not seem to be putting out the horsepower I would expect from a fresh engine.

Soooo, the question is, did I set the timing gears properly considering the non-stock cam? I've read about offset keys on this forum and I think in my newbie condition, the info did not register on my low compression brain. Jeff recommended the static timing set at 10*- 14* static... Hap talks about advancing the timing 3* to 103*. So I'm a bit confused... what did I miss here? Comments... pointers... all would be appreciated.

Ken,

I've never done this before so I'm only an armchair expert :P It sounds like you needed to "degree" your cam during install. This is a process where you measure TDC on #1 piston and set the cam for the appropriate amount of timing relative to TDC. In your case you want the cam to have maximum lift at 103 deg ATDC. I believe that each engine is sightly different depending on it's internals so just using an offset key won't get you where you need to be. It needs to be measured with a dial gauge and a degree wheel then you can calculate the appropriate offset key required and verify the results with your wheel and gauge.

Octarine services has a nice step by step visual guide on how it's done on a B series engine: http://www.octarine-services.co.uk/5.%20degreeing_the_cam.htm

Hopefully the real experts will be along to help.

Hap is talking about camshaft timing not ignition timing, cam timing is the time between the piston stroke and when the valves are fully closed ,when he is talking about 103 degrees that is the degree in which both valves are closed for combustion and the piston is at TDC. 103 is the degree where combustion occurs

its very very possible that your cam may have been re ground several times prior and in order to get the grind on the cam they sometimes shift the phase of the cam, in doing this the little dots will not line up and they may be as far as 10 degrees off, thats one tooth on the sprocket, the last Kent cam I used was 11 degrees off

get your self a timing wheel and a tcd indicator as well as a dial indicator and degree the camshaft, I have an old Vizard book that explains this very well, I could possibly copy it and send it to you or see if I can get it scanned into the computer and post it for you

10 degrees will cause lots of power loss and lower compression

A more detailed article from Crane Cams that is general enough to apply to any cam/engine combo. I like the part that explains what all that stuff is on the cam timing card: http://cranecams.com/pdf/803.pdf

Thanks for all the replies; really helpful. Looks like I've got some serious homework to attend to. The driving season is winding down, so I'll have plenty of time to get it done correctly. I trust that performance was the only casualty here and none of the components were damaged. I'm assuming that the head needs to come off... but that the work can be done with the lump in the car.
Cheers

The links Eric mentioned will do for procedure. Chris Betson's method is exactly how Peter Burgess describes cam timing in his book. I think you are going to find the cam you have will be a little flat below 2500. Degreeing it to 103 as Hap mentioned will help.

Maybe this will help, for valve timing forget about the distributor timing. Cam degreeing positions the cam intake lobes to be fully open at the degrees specified by
the cam manufacturer or based on the recommendations from an engine builder (Hap)
Lining up the timing marks on the chain wheels in theory sets the cam to have the intake valve fully open at approximately 107.5 degrees on the MGB. That is usually adequate for a stock engine. As mentioned, a reground cam may need to vary several degrees from Original specifications. To get ideal cam timing you can use off-set keys (economical, but they aren't always accurate and sometimes they have to be worked on with a file to fit the key-way) to offset the cam chain wheel to the correct position. Other methods are to use chain wheels with several slots to advance or retard the cam, another method is to use a variable cam gear. (most accurate and most expensive).

In short when you degree a cam you are making sure the intake cam lobe will be fully open with the the lobe centered at exactly 103 degrees (for your cam) after top dead center (ATDC). Use care to insure that TDC and the fully open centered position of the cam lobe are accurately measured.

Hope this helps.

Clifton

Yep, it sounds like you need to pull the cam drive and reset stuff.

You might have been confusing the advice. Hap was speaking of cam timing and from what I think I hear from you, you must have just put it back together in the standard way. What Hap is talking about is "degreeing" the cam. It is considerably more involved but not at all impossible. You are going to need a degree wheel. Beg borrow or steal on. If you buy one expect to pay about $30. A seven inch wheel will work just fine. This is going to take more than a few hours for the first time out for you but the bragging rights will be worth it.

Unless you want to invest in a vernier cam sprocket you should get your hands on several offset woodruff keys too. They come in two degree increments and you should have one each of 2, 4 and 6. Make sure that you can return the unused ones for credit.

Once you get a degree wheel in hand get back here and one of us will lead you through the process. It might also be good if you picked up a copy of the Burgess book on power tuning B engines as you will have a step by step guide at hand in case you get frustrated.

The other issue of IGNITION timing can be dealt with later and Jeff will advise you on what he wants for his distributor according to what you tell him about your engine spec.

In the mean time, relax, go get a degree wheel and rip the radiator, fan and timing cover back off so you can get to the cam drive.

Jack

If you can't find a wheel locally Jeggs has them for $24. The part number is 720-1570, page 134 of their latest catalog. Their number is 800-345-4545.

You CAN use a dial indicator to check the crank position but it isn't necessary. When you get to that part you can use several methods to insert a piston stop through the plug boss and turn the crank to full stop in both directions and then split the distance on your degree wheel. No more tools necessary except those needed to pull the thing apart, a feeler gauge set and a bent coat hanger. LOL

Jack

I had to set my timing at 20 degrees to get it to stop sputtering on exceleration. Can't make it ping, so I don't know whats up. Maybe I didn't get something right on the rebuild or my stock cam was a reground and is off a little.

twigworker Wrote:

I think you will find that cam with it's duration to have lower torque until you reach higher RPM's. To me that duration is more of a higher RPM horsepwer type cam.

Burgess's book is on order. I was hoping to have the car ready for my son's wedding this Saturday but my wife has other plans! LOL. So, in the mean time, I'm waiting for the mail carrier to deliver Power Tuning, hunting down a degree wheel and renting a tuxedo.

Thanks for all your help. I'll get back to you when I get the timing gear exposed to light.

As has been noted here on numerous threads the Burgess book is well augmented by David Vizard's book on A series engines. MUCH of the theory and lots of the specifics in David's book carry over to our B motors.

Jack

You don't mention how you drive the car, but I agree with Swamper that it will not get too excited about its job until around 3 grand. Take the car out and give it some boot, shiffting around 4 1/2 to 5 k. You may find that it is much happier around there.

I have a crane cam, and it does not even get out of bed till almost 3k on the tack. Still idles and all that, just no guts till you get a lot of rpms on the tach.

By the way, in NA, the offset keys for the timming gear are very hard to get for an MG. Do not expect that you will be able to return any either.

Pete

Once you get the cam set up right with Hap's instructions, you should be quite pleased with the engine! You may need to pull the engine to do the work though. It means you'll need to remove the timing cover to install a new cam key or sprocket. I used the Crane website as a refresher the last time I degreed an engine - if you don't do it regularly it can get confusing. Just remember that you're trying to get the valves to open earlier in comparison to the crank rotation.

If you are going to change the key, you should be able to do it in the car. I just had the timming gear off my car last week-end and it was not a problem. I used a piece of rope down the plug hole to keep the engine from rotating while undoing the crank nut. I made sure that that cylinder was on the compresion stroke so that both valves would be closed and no chance of bending the valve with the rope.

Dial indicators with magnetic bases are quite cheap and make this easy. Most speed shops sell degree wheels and as mentioned the crane site tells you how to use it all!

Pete