Lehman Head Bolt Sizes - replace with stud?

[Turbonic]

Hello All,

I'm new, and have what may sound like a few silly questions. I have my reasons!

Basically, I have just bought a 33foot boat with twin lehman 150hp econ-o-power lumps in. Yey.

Problem is the boat is a bit far away for me to find out the following at the moment.

They are 1978 engines, and I believe have 1/2" Cylinder Head bolts.

Q1: Does anyone know the other dimensions; Length of bolt, pitch of thread etc.

I ask as I need to replace one with a stud.

So:

Q2: Does anyone know of a stud that will drop in in place! - just the one stud though.

Thanks V much.
Nic.

 

[RT Firefly]

Greetings,
Welcome aboard. There are NO silly questions, my friend...

 

[Turbonic]

Ehheheheee

 

[High Wire]

For all things Lehman call Brian Smith
https://americandieselcorp.com

 

[Pete Meisinger]

You may be new to the forum, maybe new to trawlers or maybe new to boating all together.

When you become more knowledgable you will no longer refer to F.L.s as "Lumps" .You will proudly shout it from the flybridge "My boat may be old, ugly and leaky but she has TWO FORD LEHMANS in the bilge"

pete

 

[Comodave]

Welcome aboard. +1 on Brian at American Diesel. He is THE guru.804-435-3107

 

[kchace]

You cannot just use a bolt of the same size. There are many grades of bolt and very often head bolts are specially made *in addition* to the grade. Call Brian at American Diesel and see if he can get you a correct one.

Ken

 

[BruceK]

Those lovely Lehmans, assuming 6cyl, are not 150hp but either 120hp or 135hp, likely the former in 1978.
What`s the story behind needing a replacement stud? For the engine, that is.

 

[Turbonic]

I think I may have blasphemed.

What I have thought are Lehman engines are Mercraft Eco o power 150 ps engines with a date of Jan 1978. They are straight 6s, and have a borgwarner turbo each.

As for full disclosure one of the engines has been welded where one of the mid block bolts kmeankng around cylinder 3 or 4, screw into the block. This is effectively because the casting cracked away from the block (don't ask me how, as this was before I bought it)

Welding it seems has been done with the correct rods, but it won't take the torque specified in the manual for the bolts, before pulling out. I have been told this by the engineer that was tasked with the job.

I had arrived at the idea of a stud (grade eight or higher) with a 1/2" UNC thread for the block, and UNF for the resulting head nut. This is to hopefully revive the otherwise scrap block.

Other ideas also appreciated.

 

[Ski in NC]

It's probably a Ford block, but which one, who knows. You need to get a bolt out and measure. Might find a Ford tag on the flywheel housing.

In the buggered hole you can buy a bottoming tap and get the stud down as low as it will go. Might also consider putting studs in the adjacent bolt holes as the UNF threads will add some clamping force. One weak bolt with three strong ones nearby might work.

ARP makes high strength studs for cyl heads, if you get the measurement they might have something. Perkins used studs on some too. If you find one too long, just use a spacer.