The Stovebolt Site Forums The Shop Area Engine Shop 261 hydraulic lifter interchange?

Might this lifter work in a 261?

Are you certain your 261 is drilled for hydraulic lifters? I believe all blocks were drilled after a certain year (1958 and later?) but not necessarily before that.

Someone smarter than me can probably weigh in with those correct details.

In previous threads discussing your "261", the casting code indicated it was a 1960-62 block, most likely a service replacement as there was no stamped serial number.

A check of the GM Heritage site for 261 engine specifications for all model years 1960-62 indicates they were all originally equipped with "mechanical lifters" (solid lifters, not hydraulic).

Although they were originally equipped with solid lifters, I can't say if the blocks were or weren't drilled to allow for the use of hydraulic lifters???

Perhaps someone with greater knowledge and experience with the later 261's can come along and help answer your question?

I would hold off on the lifter order/purchase until more info can be provided.

Dan

DragSix or Pre68 Dave will know about the lifter compatibility for late 261s. I’m fairly certain we covered this very question a while back, but I can’t find the thread.

I think all the ones in the USA were solid and passenger cars (Pontiacs) in Canada used hydraulic (so you could use either solid or hydraulic since they'd be drilled for the hydraulics). Part of the problem in using a hydraulic lifter in a 261 meant to use solids (aside from having no oil passage) is your camshaft was designed for solid lifters.

Her is one from 2019 previous conversation on 261 lifters that supports the info that 261's did not come with the drilled oil passage to support hydraulic lifters.

There were 261's made in Canada and installed in Pontiac's that were equipped with hydraulic lifters, but I don't think that case applies here.

Dan

The only real way to tell is to look and see. I have never seen one but that does not mean that none ever were. Both of my current 261 blocks are 1959 Canadian Pontiac blocks so both are drilled for hydraulic lifters. A late 60-62 USA GM replacement truck block, I can not say for certain .

I have a 62 service replacement 261 block (according to the casting code) and it is drilled for hydraulic lifters, though when I tore it down it had hollow milk bottle-style lifters.

Given the poor quality of the hydraulic lifters available today, I can't think of a good reason to take a chance on running them. "New old stock" lifters from the late 1950's to mid 60's are a different matter, assuming you can find them.
Jerry

Where is this drilled oil passage? Is it visible without teardown?

Hy 327amc, the minimum you would have to do to confirm the drilled passage would be to tear down the engine far enough to remove a lifter from its bore and check to see if the lifter bore is drilled for the oil supply that hydraulic lifters require.

It is a large diameter passage that's drilled the entire length of the block front to rear through all the lifter bores. It's about 1/2" in diameter, I believe. You'll need to remove the pushrod side cover and at least one lifter, and use a bright light and an inspection mirror to look into the bore to see it. I don't recall ever seeing an American made 261 block with the hydraulic lifter passage, since they were medium duty truck engines, and all of them I've seen ran solid lifter cams. The Pontiac 261 engines used in Canada ran hydraulics.
Jerry

All 235’s starting in 1958 were drilled to except hydraulic lifters.
261’s followed shortly after that.
If there is no oil line behind the side cover, it is drilling to except hydraulic lifters.

Dave, is that for truck motors? The reason I ask is that 55, at least in the passenger line, was the last year for a dedicated block for solid lifters (the stick shift motors) and one for the automatic trans motors, hydraulic lifters. 56, again for the passenger line, all blocks drilled for hydraulic lifters. So did GM maintain the non drilled block for the trucks through 57?

The oil passage (to allow for hydraulic lifters) is shown below in the first image. The black arrow shows the lifter bore and the drilled passage is shown by the red arrow. There is a plug for this passageway (shown in the second image) but it is covered by the bell housing so you can't reach around and feel for it (unless your bell housing is removed). This is on the 235. Hope this helps. To see this passage you must remove the side plate (the valve lifter cover), the valve cover, free up one rocker arm (by loosening the locking nut and the adjustment screw), remove that pushrod, lift up the corresponding valve lifter and look inside the lifter bore.

Mike, Starting in 1958 all 235’s whether car or truck were drilled to except hydraulic lifters, whether they were used or not. This is a result of the new system, (that started in 58) used to supply oil to the rockers.
At this time the oil tube behind the side cover was discontinued and the oil for the rockers came through the lifter galley and up through a cast-in galley in the center of the block.
261’s did not change in 1958, but they went to this design shortly after. I was not able to document the year 261 made the change.

Many thanks. I knew that at some point the truck motors were using the same or essentially the same block as the passenger block, just with solid lifters. I just never knew exactly when that change occurred.

So if I understand your response, 56 and up passenger motors drilled for hydraulic lifters, truck 235 blocks only from 58 and up drilled for hydraulics. 261 truck blocks were drilled at some point in the later production, 261 Pontiac blocks were drilled for hydraulics.

The 261 in 60 C10 came from a 59 C60 I drove home on back roads several years ago. Has drilled lifter galley, block date March 16, 1959.

Thanks BC59!
I’ve made a note of this.

Great info thanks.