Engine Knock on a 1950 8ba

[George/Maine]

Originally Posted by Flat head charley

No rods are hitting bore skirts, need to pull pistons I guess, check wrist pin suggestions. will get back to you guys soon.

I would think .025 on each side should give you the clearance.
Stock is 3.188 plus .030 you need 3.250 little extra for stroke .025 should do it.

[Ol' Ron]

Take a piece of solder about .060" in diameter and Feed it into the cylinders and rotate the engine. This will check piston clearance.

[scooder]

Tightening the valve lash is not a good idea, isky or whoever states what clearance it should be, he's the clever guy that has been grinding and designing and developing cams for a million years. I'd say he knows what he's on about.
Set them at what he says.
It does sound to me that you have some contact going on, head to piston or valve is a guess, but I'm not stood over it, so it's a guess.
Hope you find it.
Martin.

[George/Maine]

I would guess you may only have 2 or 3 rods hitting with just a slight nick.
I would check the stroke most likely its 4" stroke.
Take some tape and wrap the rod and see wear it hits the tape.
Also is the bottom of dome even with deck height and pistons look ok.
I would guess about 1/2" long and depth of grind .025 ,taper from top .000 to .025
Like to know what you find thinking of going with new rods on my 59A with 8ba crank.
I think you got it now.

[Flat head charley]

Local builder that has been in the business for 40yrs told us to tighten down valve clearance to .010 and .013 respectively. Will be back soon. Thanks for all the great infor.

[Ronnie]

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[Flat head charley]

Hey Mart, that is exactly what is happening but only on the 1-4 cylinder side and only #3 cylinder being pronounced(1/4" wide hit with no depth). Pointy domes but do not know why they are only hitting on right side. Going to mike the depth to BDC of crank to head surface on both sides soon. Looks like a bad rebuild. Reminds me of a 1960 H-D Topper rebuild I did, lost my rear end on that one. It is the nature of the beast. Also the rods are stock Ford 8ba rods, 4-ring .030 domed pistons with inner numbers of 1058 and 93 directly below on skirt and an N on one side of wrist pin and 9-27 on opposite side of wrist pin. Can anyone tell me what these are? The crank is definitely a 48-49 Merc with 3 7/8" stroke.

[scooder]

8BA rods and 3 7/8" stroke, don't chime right. Same with a definitely 48-49 Merc crank.
48 Merc crank was same as 48 Ford, 49 Merc crank ie 4" stroke.
To get 3 7/8" stroke the normal way is to offset grind a 3 3/4" crank this will then require 21A type rods, 2" journal. I could be done by destroking a 49 up Merc crank by somebody who was insane, you'd still need the early 2" rods.
possible weld up and stroke would allow the later 8BA rods with their bigger journals. The cost of this would be excessive, but possible.
How are you measuring the 3 7/8" stroke? Does the crank have 2 oil holes per throw?
Martin.

[TomO]

I had exactly the same problem on a rebuild I had done. I blamed it on the Egge pistons and the machine shop's job of cleaning up the deck. I never resolved the problem as the no. 2 cylinder decided to develop a radial crack.

On my engine, no3 was hitting the head at idle and under no load. I removed material from the top of the piston and cleared up the idle problem. At higher speeds, both no3 and 4 pistons hit the head. The crack in cylinder 2 ended the engines life.

My engine was a 99A block with a 4" Merc crank and 29A rods.

[George/Maine]

Well after picking up a crate engine from a deceased friends family member we assembled it on a platform stand with radiator, gauges and start stop switches
Are you saying you assembled it on the engine stand as a complete engine.
You have a basket case if you got it in pieces.

[JSeery]

"48-49 Merc with 3 7/8" stroke"

I have never heard of a Merc with 3 7/8 stroke. Does not make much sense to me why someone would go to the effort to make one (assuming a stock one was never available).

[tubman]

Originally Posted by JSeery

"48-49 Merc with 3 7/8" stroke"

I have never heard of a Merc with 3 7/8 stroke. Does not make much sense to me why someone would go to the effort to make one (assuming a stock one was never available).

Wouldn't this be what you would get if you offset ground a 3 3/4" late Ford crank and used early rods? I seem to remember this from "back in the day".

[JSeery]

Originally Posted by tubman

Wouldn't this be what you would get if you offset ground a 3 3/4" late Ford crank and used early rods? I seem to remember this from "back in the day".

It could be done, just doesn't seem all that practical to go to that much work for so little gain.

[tubman]

Originally Posted by JSeery

It could be done, just doesn't seem all that practical to go to that much work for so little gain.

Seems to me to be about the only way to get any stroke increase at all before 1949 without going to expensive aftermarket parts. If there's anyone out there older than me, do you remember how much it would have cost to offset grind a crank in the 40's-50's? The rods had to cheap back then.

[JSeery]

Originally Posted by tubman

Seems to me to be about the only way to get any stroke increase at all before 1949 without going to expensive aftermarket parts. If there's anyone out there older than me, do you remember how much it would have cost to offset grind a crank in the 40's-50's? The rods had to cheap back then.

The grind most likely wouldn't be that much, but it would require new pistons with the pin moved I would think. No idea, never heard of it, and with the piston knocking issue seems suspicious.

[George/Maine]

This engine sound like a new engine sold for big bucks with new shiny stuff.
New rod 8ba would never hit only after market rods.
I think you measured from the dome top to the deck ,1/8 dome ,4"Strock.minus 1/8" equals 3 7/8"

[tubman]

Originally Posted by JSeery

The grind most likely wouldn't be that much, but it would require new pistons with the pin moved I would think. No idea, never heard of it, and with the piston knocking issue seems suspicious.

I think this is getting a little O/T, but no, it wouldn't need new pistons. Think about it; the material removed from the crank is on the inside of the journal. the stock piston would be at the top of the block at it's highest, and 1/8" down at the bottom. Thinking about it, with the price and availability of early rods back then, if you needed any crank work at all, the 1/8" stroke increase would essentially be free.

[rotorwrench]

Any stroke change required the correct piston with the pin location to match the stroke. Mercs had Merc pistons for 4 inch stroke. Special pistons would be needed for a 3 7/8 stroke or the heads would have to be modified for pop up design. All that stuff was done long ago but not so much these days.

[George/Maine]

From what I have read this guy doesn't know how to read a scale.
Top of dome to deck is 3 7/8", 4" stroke minus 1/8 drone height = 3 7/8"
I think one of the new goodie has to go loose the pistons. get flattops.

[tubman]

Originally Posted by rotorwrench

Any stroke change required the correct piston with the pin location to match the stroke. Mercs had Merc pistons for 4 inch stroke. Special pistons would be needed for a 3 7/8 stroke or the heads would have to be modified for pop up design. All that stuff was done long ago but not so much these days.

Think about it again, more carefully. With the piston/rod/crank at TDC, the distance from the top surface of the crank to the deck surface is exactly the same as stock. The extra 1/8 of stroke is picked up when the combination is at BDC. A 4 inch Merc still has the large rod journals, requiring a different piston. Remember, the 1/16 inch is taken off the BOTTOM of the journal (toward the center of the crankshaft).