1937 Buick series 40 engine rebuild question

[wowo]

Hi all,

I'm in need to rebuild my 1937 Special engine after the previous rebuild done by a machine shop in Nevada was poorly performed a few years ago with several mistakes made - making the engine seize after not even 7.000 miles on the clock. Back then the engine was converted to using insert type bearings for both mains and rod bearings. My shop here in Spain where I have the engine now is asking me for the original measurements  of the main bearing and rod bearing housings (diameter with caps bolted on). From different sources I could identify the standard specs for:

- crankshaft journal diameter (both main bearing and rods)

- crankshaft and connecting rod nominal bearing diameters

- crankshaft bearing to journal clearance

 

But I can't find the specs for crankshaft housing diameters (main and rods). Can anyone help?

 

thanks

Martin

[Pete Phillips]

I guess I'm dumb, because I don't understand the difference between "crankshaft journal diameter" and "crankshaft housing diameter". If you have the crankshaft journal diameters, the bearing sizes, and the clearance tolerances, what else is there to know?

Pete Phillips, BCA #7338

Leonard, TX.

[pont35cpe]

Rod Journal dia 1.997-1.999   bearing clearance .0008-.0018  end play .005-.010  rod bolt tension 40-45ft lb                                       Mains are all different dia. #1  2.3095-2.3115  #2 2.3725-2.3745  #3(center) 2.4345-2.4365  #4  2.4975-2.4995 #5 2.5595-2.5615 bearing clearance .0007-.0022  crankshaft end play .004-.007  main bolt tension 90-100ft lb   These specs are from a Motor`s Auto Repair Manual. This may be the information you already have.                                     

Edited March 4, 2021 by pont35cpe (see edit history)

[37_Roadmaster_C]

@wowo,  I do not have the information you want and I am not familiar with the 248. My car has the 320 and is therefore different.  The  1937  320 as stock has  insert crank main bearings and poured babbitt rod bearings. I took a quick look and found some interesting info that may help you.  Check www.egge.com and look at their offerings for your car and engine. They list a rod bearing and if you look at the details they also list an OD spec for the bearing.  I do not know if this is stock or if it is what they do if they modify rods for insert bearings.  I had them modify my stock rods for inserts and they did a fantastic job and the clearances were spot on when assembled.  Good luck!!

 

Also, what specificly failed in your motor? Did it seize pistons or bearings?

[wowo]

9 hours ago, Pete Phillips said:

I guess I'm dumb, because I don't understand the difference between "crankshaft journal diameter" and "crankshaft housing diameter". If you have the crankshaft journal diameters, the bearing sizes, and the clearance tolerances, what else is there to know?

Pete Phillips, BCA #7338

Leonard, TX.

That's what I thought as well but the shop said that knowing those specs and bearings diameter is not precised enough when working with 2-shell-bearings and they would need to know the factory  bearing housing measurements as well in order to work out correct new line bore and building bottom engine without shims later.

[wowo]

7 hours ago, 37_Roadmaster_C said:

@wowo, 

 

Also, what specificly failed in your motor? Did it seize pistons or bearings?

several problems: 

- piston clearance too tide, probably installed with factory clearance from 1937 manual but using modern pistons (needing more clearance)

- piston pins on several pistons sitting extremely tide and were not moving freely - probably creating overheating in the area

- rear main was sealed off with a rope seal when manual clearly states that on 1937 and 38 series 40 engines this seal should not be fitted. Probably slowed down the free movement of my crankshaft which cant be good for a motor

 

Insane that previous owner paid close to 10.000 bucks for this crappy overhaul, thinking it was in good hands......

 

[37_Roadmaster_C]

11 hours ago, wowo said:

several problems: 

- piston clearance too tide, probably installed with factory clearance from 1937 manual but using modern pistons (needing more clearance)

- piston pins on several pistons sitting extremely tide and were not moving freely - probably creating overheating in the area

- rear main was sealed off with a rope seal when manual clearly states that on 1937 and 38 series 40 engines this seal should not be fitted. Probably slowed down the free movement of my crankshaft which cant be good for a motor

 

Insane that previous owner paid close to 10.000 bucks for this crappy overhaul, thinking it was in good hands......

 

There are some real specific "gotya" points in these engines. The pistons are one of the most important. On the 320 at least the factory pistons were "cam ground". This means that they are not round, but slightly oval. This is done so that with the expansion of heating they will become round when the engine gets to operating temperature. If the rebuilder is not VERY familiar with this it is common for the bore to be to tight and piston drag/seizing can occur.  The rod bearings were poured babbitt and if they were modified for shell insert type bearings the dimensions would be specific to that modification. Buick upgraded to shell insert bearings in mid 1947 so it may be that those specifications were used for the modification of the rods.  Your rebuilder will need to investigate to get it right.  Just for information, my complete rebuild on the 320 cost us just a bit over $8000 and included cam and crank grinding, rod modification, new 1938 pistons, valves, guides and complete head rebuild. It also included paint pf the proper color and many small detail items I am forgetting.  With that in mind a $10000 rebuild is not out of line for a regular shop. My guy is a retired pro and still has all his equipment and does specialty work in his free time so the price is a bit lower than a pro shop.  However, the pro shop should be able to do a quality job and not have a failure in 7000 miles. 

[wowo]

2 minutes ago, 37_Roadmaster_C said:

There are some real specific "gotya" points in these engines. The pistons are one of the most important. On the 320 at least the factory pistons were "cam ground". This means that they are not round, but slightly oval. This is done so that with the expansion of heating they will become round when the engine gets to operating temperature. If the rebuilder is not VERY familiar with this it is common for the bore to be to tight and piston drag/seizing can occur.  The rod bearings were poured babbitt and if they were modified for shell insert type bearings the dimensions would be specific to that modification. Buick upgraded to shell insert bearings in mid 1947 so it may be that those specifications were used for the modification of the rods.  Your rebuilder will need to investigate to get it right.  Just for information, my complete rebuild on the 320 cost us just a bit over $8000 and included cam and crank grinding, rod modification, new 1938 pistons, valves, guides and complete head rebuild. It also included paint pf the proper color and many small detail items I am forgetting.  With that in mind a $10000 rebuild is not out of line for a regular shop. My guy is a retired pro and still has all his equipment and does specialty work in his free time so the price is a bit lower than a pro shop.  However, the pro shop should be able to do a quality job and not have a failure in 7000 miles. 

hmmm, but aftermarket, modern pistons from Bobs Automobilia etc. should be different I'd expect,. Are you saying they are still prone to go from oval (cold) to round (hot)?? From doing some online research I gathered that one big troublemaker has often been to apply factory piston clearance from the 30s to fitting modern aftermarket pistons......

I agree, a full engine overhaul costs money but its obviously very frustrating to see a 10K overhaul leading to an engine being blown up after only 7.000 miles....

[37_Roadmaster_C]

@wowo,  I expect that modern pistons are different and clearances need to be adjusted as needed. If nothing else, the alloy used in the piston is different and therefore the expansion ratio will be different. With that in mind, you are exactly correct. I do not know if modern pistons are cam ground or not, but the clearance issue is still the same. If the cylinder bore was to tight for the modern piston then the problem you had is expected.  Every major aftermarket manufacturer has specific information about fitment of their parts.  If the information is not supplied with the parts it is available with a phone call, email or on the website. My guy dealt directly with Egge for the pistons, rod modifications and I believe cam grind so any information came from them directly. If the parts come from a place like Bobs I would them to either supply the information, get the information for you or point you to their supplier so you could talk with them about the issues.  I do not know what my rebuilder did but he has old time knowledge and his work is 100% guaranteed no questions asked.  I hope some of this helps. Keep us posted as we like to hear the outcome!!