371 Piston?
#1
371 Piston?
Teach me please.
I recently took the engine apart because it was a broken piston ring.
The casting number on the cylinder block identifies it as 1957 371.
The cylinder head is a 1962 394.
The manual says the cylinder bore is 4 inches, but this engine had a domed piston of about 4.183 inches.
Pistons don't have numbers.
It seems that the cylinder is enlarged considerably.
Which piston are you using?
Is it the classic hop-up of the past?
Please help me.
Thank you.
Please excuse my strange English.
from Japan.
I recently took the engine apart because it was a broken piston ring.
The casting number on the cylinder block identifies it as 1957 371.
The cylinder head is a 1962 394.
The manual says the cylinder bore is 4 inches, but this engine had a domed piston of about 4.183 inches.
Pistons don't have numbers.
It seems that the cylinder is enlarged considerably.
Which piston are you using?
Is it the classic hop-up of the past?
Please help me.
Thank you.
Please excuse my strange English.
from Japan.
#2
That's exactly what this sounds like.
62 thru 64 heads flowed better and would bolt on 371 blocks.
4.183 bore on a 371 does sound like a lot. But it was common to bore them to 4.125 and use 394 pistons.
These old blocks had very thick cylinder walls, so I suppose it was possible.
I would be leery about boring it any further, unless you have the cylinders "sonic checked"
62 thru 64 heads flowed better and would bolt on 371 blocks.
4.183 bore on a 371 does sound like a lot. But it was common to bore them to 4.125 and use 394 pistons.
These old blocks had very thick cylinder walls, so I suppose it was possible.
I would be leery about boring it any further, unless you have the cylinders "sonic checked"
#3
Thank you for teaching me.
Does that mean that the 394 standard has a 4.125 bore, so a 0.060 oversize piston is used?
Do you sell dome type pistons?
Or is it a diversion of something?
Enlarging the bore any further may be a concern.
Does that mean that the 394 standard has a 4.125 bore, so a 0.060 oversize piston is used?
Do you sell dome type pistons?
Or is it a diversion of something?
Enlarging the bore any further may be a concern.
#5
Do you have a shop over there that can sonic check the thickness of the block?
You may be OK, but it's wise to check.
A domed piston sounds like it is really high compression. You may want to get a set of flat top pistons, and even then you will need 93 octane fuel.
I don't make or sell any parts. However here is a link to a company that makes custom forged pistons;
Home - RaceTec Pistons
You may be OK, but it's wise to check.
A domed piston sounds like it is really high compression. You may want to get a set of flat top pistons, and even then you will need 93 octane fuel.
I don't make or sell any parts. However here is a link to a company that makes custom forged pistons;
Home - RaceTec Pistons
#12
Maybe I'm misunderstanding, but are all the pistons this size not just this one? 60 over would be close but sonic check as mentioned above should very well be done. That era engine were known for their thick blocks, but that is a bunch for a 371..Tedd
#13
That sounds like the stamped in number. There should also be a casting number at the back near the transmission. I dont have a way to identify the stamped number but I think Joe does so hopefully he will see this post.
#14
All pistons are the same size.
#15
That is the stamped engine unit number, and is the correct format for a 1957 Olds 371. All 1957 Olds engine unit numbers started with the letter "A" followed by a six digit sequence number. I assume this is on the driver's side on the block deck surface, correct?
The block casting number for a 1957 371 should be 568929.
The block casting number for a 1957 371 should be 568929.
Last edited by joe_padavano; July 9th, 2023 at 07:26 PM.
#17
The 394 used a 4.125" bore. 0.060" oversize pistons for a 394 would be 4.185", which sounds a lot like what you have. Your cast domed pistons are aftermarket. I have no idea who made them. In the late 1950s and early 1960s the first gen Olds V8s were the go-to performance motor for hot-rodders and there was a wealth of aftermarket performance parts available. I suspect that it is unlikely that you will find a match for that particular piston today, unless you get really lucky and find one or a set on ebay. As others have noted, I'd sonic check the block before putting any real money into it. The first gen Olds V8s were thickwall blocks, so the massive overbore on a 371 might not be an issue, but you'd better check. You'll likely be buying a complete set of 394 pistons if you can't find one to match.
#18
Thanks for the detailed explanation.
I want to build a durable engine,
I'm thinking of using the new 394 cylinder sleeve.
Bore is 4.125.
The piston is a dish type.
I don't race, just run on the street.
Is there a better way?
I want to build a durable engine,
I'm thinking of using the new 394 cylinder sleeve.
Bore is 4.125.
The piston is a dish type.
I don't race, just run on the street.
Is there a better way?
#19
So you are saying that the other seven cylinders are 4.125 and this one is oversize? Yes, a sleeve would be a good solution in that case, assuming the remaining wall thickness is adequate.
#21
OK, let's start again. This engine was assembled from mis-matched parts. If you plan to put any money into it, check EVERYTHING. Start with sonic testing cylinder wall thickness. If it's sufficient, just get a new set of 0.060" over pistons for a 394. There's no need to spend any money on sleeves, and frankly I doubt there's enough wall left to bore out enough to install those sleeves. Once you buy new pistons, you'll need to check the compression ratio. This will require a mockup of the short block so you can verify deck clearance to the new pistons. You should CC the heads to verify chamber volume. I would also have the rotating assembly balanced with the new pistons, since they are almost certainly a different weight than the old ones. Once things are together, verify correct pushrod length and rocker geometry on the valve tips. Do all that and you should have a stout street motor that you'll be happy with.
#25
Egge charges forged prices for cast pistons ($728 a set!). Google shows these, but even for that price I'd talk to someone like Mahle or Icon or Diamond and get exactly what you need in a higher quality piston.
https://www.bopparts.com/1959-1960-1...-8-pieces.html
https://www.bopparts.com/1959-1960-1...-8-pieces.html
Last edited by joe_padavano; July 10th, 2023 at 02:03 PM.
#26
There is a pretty informative Rocket V8 thread over on H.A.M.B.
In particular, note this:
I'll also note that 394 pistons have a 1.765" compression height and a 0.981" pin diameter. Olds 455 pistons have a 1.750" compression height and a 0.981" pin. Deck the block and you probably make up the compression height difference.
In particular, note this:
A 57 could take .125 bore (394 size) and with that 59 crank .250 offset
ground stroke its over 400 cubes. The 394 piston could be used.
ground stroke its over 400 cubes. The 394 piston could be used.
#27
There is a pretty informative Rocket V8 thread over on H.A.M.B.
In particular, note this:
I'll also note that 394 pistons have a 1.765" compression height and a 0.981" pin diameter. Olds 455 pistons have a 1.750" compression height and a 0.981" pin. Deck the block and you probably make up the compression height difference.
In particular, note this:
I'll also note that 394 pistons have a 1.765" compression height and a 0.981" pin diameter. Olds 455 pistons have a 1.750" compression height and a 0.981" pin. Deck the block and you probably make up the compression height difference.
All first generation Olds engines had full floating pins.
#28
#31
#32
My 371 is bored to 4.125 and has Jahns pistons in it. Look familiar? Turn the pistons upside down and you should see a cross hatch reinforcement and the words Jahns cast into it. My catalog does not show that piston but it may be under 394 not 371.
#33
My 371 is bored to 4.125 and has Jahns pistons in it. Look familiar? Turn the pistons upside down and you should see a cross hatch reinforcement and the words Jahns cast into it. My catalog does not show that piston but it may be under 394 not 371. If it ran fine and just broke a ring replace the rings hone everything and move on. If it scored a cylinder and the rest are fine sleeve, Hone, new rings and freshen it up. Mine will be sonic checked to see if I can go 185 but will be sleeved on 2 cylinders otherwise.
Thread
Thread Starter
Forum
Replies
Last Post