Wheelmang

Rebuild of a 1926 DB 4 Cylinder

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The last engine I did a full rebuild on was either a 460 Lincoln or a slant 6 Dodge. It was that long ago that I do not remember which one was last but both cars were a long way from being antiques when the rebuilds were done. So - a lot of questions now and I am sure many more to follow as this project progresses. 

So here we go!

I still need to drop the pan and make sure that there is nothing internal that will prevent me going forward this rebuild. That will likely be in a couple of weeks. In the mean time some pre-planning and questions. I really hope to save this engine as I am pretty sure it is original to the car. 

- Will I be able to use a connecting rod from another engine or should I purchase new?  I have at least 8 spares.

- Are the prices I have, so far, about right?

- Any type of guesstimate for what to expect on the block labor? The local speed shop is out until Thursday. 

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- My welder says the crack may be better serviced by brazing? The crack appears to be only on the area around the pan bolt. The oil pan dent will need some hammering out as well.  Your comments pro or con on brazing please. I hope to grind it down smooth before sending the block to the machine shop. 5ac26591afad3_CrackedBlock.JPG.cd05583c42cbced158845b10ba778902.JPG

 

- Since main and rod bearing are all going to need re-babbitting is keeping them with current position critical? I presume at least number four rod is going to need replacing and expect the         bearing will not be usable. 

- I have a spare crank shaft. If the current one is damaged is there any reason the spare cannot be ground and used for replacement even though not from this engine originally?

- Should I pull the camshaft? If so what additional processes with be required? How is the cam retainer, on the side of block under the generator, removed? 

- Remove engine and transmission as an assembly or disconnect transmission first. 

 

Please advise of anything I am missing. Still only in the planning stage but would like to eliminate as many surprises as possible. I still have the back up spare engine if this build just is not feasible but that will need most of what I will need on the engine here. Just has things like cam and crank and rods that are original. Oh and no crack!

I deeply appreciate the expert guidance from this membership. Progress pictures will be posted as they happen and will likely be a few months in process. 

Thanks 

Paul

 

 

Edited by Wheelmang
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38 minutes ago, Spinneyhill said:

I think we have seen prices like $225 per bearing for Babbitting. See the technical forum?

Thanks I did a search for Babbitt on the whole forum but nothing came up specific to pricing. 

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I would look into cold metal stitching as a preferable alternative to welding or brazing.  I have had very satisfactory results using this method.

 

I couldn't help noticing the crank grind tolerance of 0.010".  The crank needs to be much more accurately ground in my opinion.   0.001 " max.

 

Ray.

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Using another crank will not be a problem as long as the new mains babbitt is line bored/reamed to the appropriate diameter.  The crank should be checked for cracks and bend too.  I see no reason not to use the other rods you have so long as they are checked for cracks and straightness (I don't recall ever seeing new rods for sale).  It would also be good to have them all weigh near the same too.  As for the cam, I know I've seen lift specs, probably in the MIM.  

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Interesting info. What are the variation tolerances and how is the weight removed or added to adjust. Doesn’t sound like something to be done in a home shop. I’ve never had an engine balanced and blueprinted and won’t be doing it here but is this part of that process?

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6 hours ago, Wheelmang said:

Interesting info. What are the variation tolerances and how is the weight removed or added to adjust. Doesn’t sound like something to be done in a home shop. I’ve never had an engine balanced and blueprinted and won’t be doing it here but is this part of that process?

 

It all depends on what you want to spend!   Your engine (and almost all stock engines) came from the works without having been balanced.  If however you want your rebuild to be the best it can be then go for balancing. The most you can expect is a smoother running engine with a longer lifespan as the absence of vibration is a real benefit. Performance will still be limited.

 

Ray.

 

 

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So maybe on my 26 DB 4 cyl rebuild I should go for balanced, blueprinted, polished and ported, custom headers and just for that little extra boost a turbo with a nitrous system hidden under the back seat. Whada-ya think?  Nah I don't think so. Balanced sounds good though. 

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If you go with new pistons and pins, I would expect them to be pretty close to each other weight-wise.  It was when you mentioned the possible mixing of rods from 2 or more engines that I'd be a little nervous about the rods being close to the same weight.  Production variations and all that...  

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The sheer weight of the standard flywheel is enough to smooth out most variations.  Really, it is not until you start lightening the flywheel as part of a programme to improve performance that you gain any real benefit from balancing etc.  Unfortunately, these old style engines lack the pressure fed bearings needed for performance tuning.  

 

Ray.

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19 hours ago, MikeC5 said:

If you go with new pistons and pins, I would expect them to be pretty close to each other weight-wise. 

 

And it should be mentioned that balancing rods, for example, isn't just a matter of putting them on a scale, but rather having a set up that allows you to weigh each end of the assembly separately. 

 

And I agree that such tolerances on these engines isn't critical.  A standard DB 4 cylinder is good for 40 miles per hour, a so-called "fast four" another 5 miles per hour in stock configuration (and something over 100 miles per hour if you're talking the Montana guys!)

 

And, I can tell you from personal experience that, at those speeds, vibration in the engine is not only the least of your worries, but all the other vibrations in the car will have you more than occupied!

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Here is a pic of how to balance the big end of the rod.

 

IMG_3143_1.jpg.5bd7f6125b984361d25a35f77073b32e.jpg

 

A basic balance is probably only required if the rotating assembly is a mis-match of parts from various sources or engines. I would also agree that the huge flywheel negates the need for a detailed balance for our flat head engines, unless you are racing.

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Getting a little closer to starting this rebuild now. This question may be way out there but - are there any modifications that can be done to a 90+ year old 4 cylinder that will add even a few HP? Would boring it out even if it doesn't need it help? Just thinking, if I can add even 4 - 5 HP it is a 10% increase. I live in the foothills of the Appalachians and would like to make it to the top of some of the hills in at least 2nd gear.  

Thanks for looking!

Paul

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Better grind on the camshaft.  Quite easy when appart and doesn’t impact the ‘originality’ of the car.

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One of the things you could do to try and prevent a cylinder head gasket failure on climbing those hills would be to make sure the surfaces of the block and head are perfectly flat.  You may well find that a few thousandths of an inch may need to be removed to achieve this.  The effect of this skimming would be to slightly raise the compressions which  in effect will slightly increase the power output.  Be careful though because with an engine this of this age, the surfaces may already have been skimmed.  Too much compression and there is a risk of damage to the crankshaft big end and main bearings; certainly it can increase wear and contribute to head gasket failure.

 

When it comes to cars of the vintage (pre 1930) period most are devoid of pressure lubrication to the crankshaft and camshaft.  You will notice that the oil pressure gauge  only reads 4 psi.  This is because all you are being told is that the oil pump is working.  It does not mean that there is that amount of pressure at the bearings.  This method of lubrication is called "splash" for somewhat obvious reasons.  The upshot of this is that engine performance  was limited. 

 

Ray.

  

Edited by R.White (see edit history)
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14 hours ago, R.White said:

One of the things you could do to try and prevent a cylinder head gasket failure on climbing those hills would be to make sure the surfaces of the block and head are perfectly flat.  You may well find that a few thousandths of an inch may need to be removed to achieve this.  The effect of this skimming would be to slightly raise the compressions which  in effect will slightly increase the power output.  Be careful though because with an engine this of this age, the surfaces may already have been skimmed.  Too much compression and there is a risk of damage to the crankshaft big end and main bearings; certainly it can increase wear and contribute to head gasket failure.

Ray.

  

Thanks Ray:

To the best of my knowledge the engine has been down before. Two different size head studs. In addition the head was flattened .010 when I did the valves. Is there too much at risk to go ahead and have up to an additional .10 removed from the block? Is there any way to tell if the block has been shaved before? I am really trying to keep this original engine with the car but have a spare block if needed. 

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Since you have a '26 model, does it have the old 3 main bearing crank, or the "C" 5 main bearing engine? (The changeover occurred around the middle of July.)

 

If you have the 3 main bearing engine, be very careful about trying to increase horsepower too much, because the bottom end can't take it.  I knew a DB guy who installed a Roof OHV cylinder head on his '24 model and promptly blew up the bottom end.

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To check for valve clearance, take off the head, remove the gasket, put some blue tack in the head above the valves, sit the head on with no gasket, turn the engine over a couple of turns. The squeezed blue tack will tell you how much clearance you have. You might have to put some nuts on to hold the head down.

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1 hour ago, Spinneyhill said:

To check for valve clearance, take off the head, remove the gasket, put some blue tack in the head above the valves, sit the head on with no gasket, turn the engine over a couple of turns. The squeezed blue tack will tell you how much clearance you have. You might have to put some nuts on to hold the head down.

 

I have not come across that method before.  If I may suggest an alternative would be to remove a valve spring and set the cam so the valve is fully open.  Without the spring pressure you could determine how much clearance there is by lifting the valve.  Or have I missed something?

 

Ray. 

Edited by R.White (see edit history)

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3 hours ago, R.White said:

Without the spring pressure you could determine how much clearance there is by lifting the valve.  Or have I missed something?

 

Excellent idea! It will give a much more accurate measure than my bush mechanic's method.

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Really - do the valves even come close to the head on these old side valves?  I would have thought that even with a few ‘skims’ of the block and head you’d still be able to drive a bus through the gap.  But perhaps the earlier engines are a little tighter?

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Good point Rich.  This is probably a solution to a non existent problem.  

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