37 replies to this topic

[madaboutcherry]

i need to fit new guides to my cylinder head.
is this something i can do myself, and do i need to need to recut the valve seats, or can i just lap them in?

[998dave]

No, well, maybe.

Valve guides need pressing in, and may need new valves too, if you change the valves they'll need lapping, (to be fair, if you're removing the valves to change the guides, you should consider lapping the valves anyway).

Also new oil seals on top.

Dave

[mini7boy]

The valve guides also need to be reamed after installation to prevent valves from seizing in the guides.

Valve guides are often produced slightly off-center unintentionally. Even if your new guides are dead center, the previous ones may not have been, thus causing your seats to be off center with respect to the new guides. For this reason alone, the valves should be recut, not just lapped, regardless of how fresh the seats look.

a job best left to an auto machine shop.

[Cooperman]

Press the guides into the head with the top of the guide 0.59" (15.1) mm above the machined surface of the head adjacent to the guide. You can be plus or minus about 0.010" on this dimension without worrying. I do no. 1 then no. 8 very accurately using a digital vernier depth gauge, then use a straight-edge to do the other 6. It's quite easy really.
If you are fitting the steel valve guides, you usually don't need to ream out the guides, but the phosphor-bronze and manganese-bronze guides do need to be reamed. From memory the size is 9/32" (0.28125"), but check this before doing it.
Then the valve seats must be re-cut to ensure the seats are central in respect of the valve guide centre line. Any good machine shop can do this, but it is advisable to supply them with an inlet and an exhaust valve to match up to the seat. If the engine has done a few miles, this is an ideal time to change all the exhaust valves, although the inlets may well be OK.
Lap the valves in and use paraffin to test for a good valve seal after fitting the valve springs and caps. If any do leak, then take them out and lap some more - it's worth it in the end.
I hope this helps,

Peter

[Nightrain]

As Cooperman's said above, never needed to get the seat's re-cut yet. Just do a good job with grinding them in and check after with parafin.
Best way to fit the guides is to make yourself suitable drift so there all the same height ! Unlike the example below.

Attached Files

•  KCHeadGuideHeight.jpg   21.83K   67 downloads

[MRA]

As far as I am aware we are the only company that manufacture a tool for setting the valve guide height to 0.591 +-0.005"

[mini7boy]

as Cooperman said "Then the valve seats must be re-cut to ensure the seats are central in respect of the valve guide centre line".

Why take a chance on either existing seats or new valve guides that are off center. We are not talking about big money here.

Best to just recut the seats and make sure that seats are on center with guides. Job done....properly.

Why take a chance on ANY guide being "crimped" during installation? At least run the reamer through all guides, regardless of material, just to make sure you won't seize a valve
and wreck the head if not the engine.

For no good reason, valve guides are often machined incorrectly and off center(at least). No need to assume that their bore is correct.

[MRA]

Running a reamer through a valve guide just to make sure is like putting an extra 20psi of air in your tyres just in case they leak !...........

Any good quality valve guide should NOT need to be remachined....

Reaming is not the correct way to do the job as there is insufficient material left for the reamer to work correctly.

[madaboutcherry]

i,m very confused now.
i was hoping to do the work myself as i have completly restored my 68 mk2 myself.
perhaps i should get a reconditioned lead free head.
anybody know where to get one and how much to pay?

[Nightrain]

Running a reamer through a valve guide just to make sure is like putting an extra 20psi of air in your tyres just in case they leak !...........

Any good quality valve guide should NOT need to be remachined....

Reaming is not the correct way to do the job as there is insufficient material left for the reamer to work correctly.

Surprised at this statement mra, always best to run a reamer through after fitting, as much as I hate to agree with the boy. We don't or at least I've never had any problems with offset bored bored guides (when there not supposed to be) though and as I said above never had to have a seat re-cut. But then again thats probably down to careful selection of parts.

[mini7boy]

Running a reamer through a valve guide just to make sure is like putting an extra 20psi of air in your tyres just in case they leak !...........

Any good quality valve guide should NOT need to be remachined....

Reaming is not the correct way to do the job as there is insufficient material left for the reamer to work correctly.

Surprised at this statement mra, always best to run a reamer through after fitting, as much as I hate to agree with the boy. We don't or at least I've never had any problems with offset bored bored guides (when there not supposed to be) though and as I said above never had to have a seat re-cut. But then again thats probably down to careful selection of parts.

you are dead wrong, MRA. You absolutely need to ream A-series guides in order to compensate for any crimping that occurred while pressing them into the head.

off-center guides are not only an A-series problem. I can't explain why guides are machined incorrectly, but it's a fact. By re-cutting the seats after installation of new guides, you guarantee that the seats
and guides are concentric. Don't trust me. Ask people who port cylinder heads for a living.

The thing about off-center guides is a double whammy. Unless you recut the seats, you're screwed if you install off-center guides, but you're also screwed if you remove off-center guides from a head which had its seats recut to make them concentric with the old guides. Any engine, especially one built for performance, should always have its seats recut after new guides are installed.

[MRA]

Running a reamer through a valve guide just to make sure is like putting an extra 20psi of air in your tyres just in case they leak !...........

Any good quality valve guide should NOT need to be remachined....

Reaming is not the correct way to do the job as there is insufficient material left for the reamer to work correctly.

Surprised at this statement mra, always best to run a reamer through after fitting, as much as I hate to agree with the boy. We don't or at least I've never had any problems with offset bored bored guides (when there not supposed to be) though and as I said above never had to have a seat re-cut. But then again thats probably down to careful selection of parts.

you are dead wrong, MRA. You absolutely need to ream A-series guides in order to compensate for any crimping that occurred while pressing them into the head.

off-center guides are not only an A-series problem. I can't explain why guides are machined incorrectly, but it's a fact. By re-cutting the seats after installation of new guides, you guarantee that the seats
and guides are concentric. Don't trust me. Ask people who port cylinder heads for a living.

The thing about off-center guides is a double whammy. Unless you recut the seats, you're screwed if you install off-center guides, but you're also screwed if you remove off-center guides from a head which had its seats recut to make them concentric with the old guides. Any engine, especially one built for performance, should always have its seats recut after new guides are installed.

Sorry if I have upset you, but I have been doing it my way for the best part of 30 years.

Using a reamer is still the wrong tool for the job, and is a major contributor to the many heads I see with so much clearance its unreal......... if you need to resize then use a roller burnisher.... but as these are consderably dearer and most people haven't got a clue as to what they are...... companies that use them just tell them they have reamed them and companies that don't use them carry on in blissfull ignorance

Remember the crank thread form issue ??

Secondly what materials do you use for your valve guides ?

If you are trying to ream out 0.0001" then firstly how are you checking where you are machining material from ? this issue is comparable to the guy in the trye shop who guns up your wheel nuts to 80lbf ft and then checks them with a torque wrench set at 45lbf ft

Valve to Guide clearance should be a 0.0025"for inlet and 0.003" for exhaust, the guide "crimping" as you call it is misleading, a sit will not be more than a few 10ths (ten thousandths) of an inch and well within tolerance, by reaming it you will be removing about 0.003" which is well outside of the tolerance....... but the valve fits !!

As I say, I do it my way I will continue to do it my way and if you choose to continue to do it your way then it's your decision and I wish you all the best

[Nightrain]

Remember the crank thread form issue ??

I remember teaching everyone on here that they where using the WRONG tap, in fact ALL the experts on here where wrong.

[MRA]

Remember the crank thread form issue ??

I remember teaching everyone on here that they where using the WRONG tap, in fact ALL the experts on here where wrong.

Precisely (myself included) however I do know about reaming and machining and tolerances and measurements etc......

I fell in to the same trap that most people fell in to about the 5/8" x 16 Whitworth thread tap for the crankshaft by using a 5/8" uns tap oops..... but it would seem that the foot is in the other shoe.......... and talking shoes, if your shoes are too tight do you go out and buy a pair two sizes too big just because you can get your feet in to them ???

Regards Martin

[madaboutcherry]

i give up, i,m buying a fiesta!