BogusSVO

iTrader: (1)

Building a Mazda BP Head


If you have not read
https://www.miataturbo.net/engine-pe...pection-70069/

https://www.miataturbo.net/engine-pe...bp-head-70149/

The porting work is done, the head has been cleaned again.
The bronze guides installed.


The guides have an unfinished ID, so the valves will not fit in the guide.
Time to get the guide hone out.


I use one of my pilots as a gauge to set the guide ID.

Hone until the pilot fully seats, I also check the top of the guide this way.


Now the head will be washed yet again.
Now the seats can be cut.
Now there is an issue…
Went to lap a valve in to check valve seat placement.


The valve did not seat. At all!



Here is the issue, the casting hump on the valve is hitting the guide.


The close tolerance of the bronze guide to valve stem was not figured to work with stock valves, Most all quality stainless steel valves will not have this casting hump.

So now to fix this issue, machine the valve, or machine the guide? Machining the guide seems simpler.

A slight taper in the bottom of the guide will do.


Now the valve fully seats, and I can check seat placement.


Now the seats are cut, each valve is hand lapped.




With the valve work done, the head can be surfaced.








A total of .007 was removed from the head.

Now the head is assembled, valve tip height is checked along with spring installed height.
Viton blue hi-temp valve stem seals were installed.


Along with the Brian Crower valve springs for testing on the BP head.

Stock valve spring retainers were used.


Buckets, shim pucks, and cams are installed to check valve lash.


It is a bit easier for me to set lash since I have extra pucks.

What is needed to check lash, feeler gauges and a sharpie

Lash is checked.

It is some simple math and measurements to get the lash set where needed.

Now the head is done!
Placed in a box and shipped back!

aaronc7

iTrader: (8)

sweet. can't wait for mine to get done!

Der_Idiot

iTrader: (2)

Man, I love reading your walkthroughs. Always so much information.

Oscar

iTrader: (2)

So, silly question maybe. I want to swap the lifters from my 99 head with the 949 shim-under-bucket lifters. Any prediction on the amount/size of shims I'd need to get in order to have the lash set correctly, or is it a matter of buying all the thicknesses 4034893 times (at $5 each or so) and build a paperweight from the leftovers? Apparently 949 doesn't take returns on these and I don't want to have my build delayed by ordering more shims because I didn't get the correct ones the first time.

TheScaryOne

iTrader: (3)

Why don't you go shimless? IIRC the Ford Zetec lifters fit.

https://www.miataturbo.net/engine-pe...ere-buy-67555/

Landrew

iTrader: (2)

Any more to say on those Crower springs?

GTurbo

iTrader: (1)

also curious on this one.


Thanks for sharing all the info. Im in the middle of my head build right now and I feel like people like to hide information from DIYers to get business. Great contribution!

Amellrotts

iTrader: (2)

Am I out of line to ask what you charge to do a head like this on an open forum? If so, sorry.....please pm me. If not, thank you.

TheScaryOne

iTrader: (3)

You should probably try finding a machinist who does his own lash caps. This would be the easiest for you and would require the least amount of parts purchased.

Another idea would be to order a full set of the shortest lash caps, check your assembled lash, then figure out how much thicker each cap needs to be to get within specs.

BogusSVO

iTrader: (1)

I have a couple sets being run, it looks good so far. But I want to get a bit more feedback, and miles in them before I give them the ok.


You can swap the pucks around, just measure the thickness and swap around to get as many in spec, then note what you you need thicker or thinner.

If the valves are ground, and the seats cut, that will close up the lash.

crowder92

iTrader: (1)

Isn't there a concern with premature cam failure caused by mis-matching used lifters and lobes? On pushrod V8's this is a big no no, but it rarely gets mentioned on OHC engines.

TheScaryOne

iTrader: (3)

This is a big no on pushrod engines because the lifter rides directly against the cam and the surfaces wear together. There is no replaceable wear surface like we have with our shims. IIRC, the shims are softer than the cam, so they become sacrificial parts, right?

I had a Taurus SHO with the DOHC V6, and the common knowledge in that community suggested re-using old pucks by flipping them over. The wear is primarily focused on the center of one side of the puck, and flipping them gave you a new wear side and maintained the installed thickness of the shim.

I don't think this would apply with the shim under buckets or shimless lifters. I'd make sure each of those went back into the hole it came out of.

I was under the impression he was asking about shim under buckets, which come without lash caps.

GTurbo

iTrader: (1)

Yes, I was talking shim under buckets. AFAIK they cant exactly be stacked to find proper lash height?

949racing is right down the street from me fortunately, assuming they arent dropped shipped I can always buy a couple of them at a time to find the correct size?

Although I wish this wasnt the only option, in for any other ideas?

NiklasFalk

iTrader: (1)

6mm lash caps are plentiful, and grinding them to the right height is no rocket science (need a careful machinist though).
Nothing Mazda specific at all.

Assemble using a know set of lash caps (preferably a set that have lash on all valves), measure and buy/grind lash caps to suite.

hustler

iTrader: (6)

Bauce thread. I have a spare VVT head now, btw. It could make it's way to your shop in a couple years. I went with OEM refinished on this one since I'm out of cash.

TheScaryOne

iTrader: (3)

This seems to me to be the only way to do it if you can't have the caps ground by a machinist to height, and don't know the assembled height of the factory lifter and shim. The shortest (thinnest?) lash caps should have lash on every valve. Measure the assembled lash (which should be freakin huge) and do the math to figure out how thick you need each to be.

Hypothetical Example: Lash with 1 mm cap (~.0394 in) is 30 thousandths on one of the intake valves. Say you want the loose end of specs at 9 thousandths, so you'd need to order a cap that is 21 thousandths thicker. .021 in is ~.533 mm, so you'd order either the 1.5 mm cap (probably too loose in this example), or the 1.55 mm cap.

Also, you're better off doing this with a metric feeler gauge and not dealing with Mazda's unit conversion rounding.