SOHC head bolts - wrong length

[mpgFanatic]

1994 Protege, old cylinder head bolts = approx 106mm long.

Purchased a replacement set from Rock Auto:
Fel Pro ES72846, they measure 120mm, so I sent 'em back.
Purchased another replacement set:
Mahle GS33556, they cross reference ES72846 on the package, and... they're also 120mm long.

I could fabricate 14mm spacers, but that's hokey. What's the story? My guess is some non-engineer consolidated part numbers, and the parts books have been incorrect ever since.

Anyone know a proper part number for the correct length bolt set?

Thanks!

[mpgFanatic]

findings, for posterity

Wow, no one has seen this problem before? Given that the cross reference to Mazda's B660-10-135A apparently affects just about every 1.6L and 1.8L they made... from 1988-2005, including Proteges and Miatas without regard to number of cams... you'd think an incorrect part number would be discussed all over the Internet. Guess I'd better describe a solution.

The first sanity check: after I got the head back from the machine shop, here are sample engine measurements that a bolt would need to span from head to tip. This was in an attempt to prove whether the 120mm replacements might actually fit:

2.3mm washer
66mm cylinder head
0.8mm head gasket
42mm thread depth til bottoms
(there is 5mm additional unthreaded hole beneath that)

--- therefore, any bolt longer than ~110mm will bottom before it clamps ---

That implies the 106mm chosen by Mazda engineers is very reasonable.

I wrote to Fel-Pro technical support and received exactly zero response. They apparently don't sell enough 30-yr-old Mazda head bolts to care that their application listing is incorrect.

The Mazda dealer lists a part number, but $15 each?? I am curious to know how long they are, but haven't gotten around to calling yet. At that price, I may as well look for ARP studs. And this is just a Daily Driver; doesn't even pretend to be a race car.

Shortening a head bolt seems like a really dumb idea. Hardness, temper, thread length...

Where can we find any head bolts that are M11-1.50, 106mm "critical length" and at least 30mm thread length? Thankfully, O'Reilly Auto Parts shows pictures and dimensions. Part number ES72858 for a 1985-1990 Pontiac Grand Am is the most promising.

I bought a set -- roughly $30 -- the bolt is about 1mm shorter than the 106mm they specified. The 15mm head (instead of 12mm) shouldn't be a problem because even a 17mm socket will fit between the valve springs. The thread pitch is perfect. However... only 8 of those bolts are the right shape/length, so in order to obtain 10, I'll need to purchase a second package.

Someone at Fel-Pro might wonder how many Pontiacs are being repaired.

What an amazing journey, for something that should have been a straightforward repair.

[Rick505]

If you can cut them down to the correct length will you still have 30mm of threads? If you do I don't see any problem cutting the 120mm bolts down to size. If you cut them with a hacksaw with a high quality, fresh blade you shouldn't have any problems. Also you will want to thread a die of the correct pitch on to the bolts, all the way up to the head of the bolt. Once you have cut the 14mm off run the die down to clean up the rough edges and you should be good to go.