Rebuild of a 1926 DB 4 Cylinder

[Wheelmang]

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. 

- 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. 

 

- 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 April 2, 2018 by Wheelmang
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[Spinneyhill]

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

[Wheelmang]

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. 

[R.White]

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.

[Wheelmang]

Thanks Ray. I will check on the specs for the crank. .001 sounds more likely.

[MikeC5]

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.  

[Spinneyhill]

In fact, rods plus pistons plus pin plus rings should all weigh the same.

[Wheelmang]

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?

[R.White]

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.

 

 

[Wheelmang]

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. 

[MikeC5]

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...  

[R.White]

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.

[trimacar]

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!

[R.White]

Those Montana boys have done it again !   Last year they set a new land speed record!

 

https://vortechsuperchargers.com/blogs/main/the-montana-dodge-boys-set-multiple-land-speed-records-with-vortech-supercharged-power

 

Ray.

[maok]

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

 

 

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.

[Wheelmang]

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

[RichBad]

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

[R.White]

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 May 9, 2018 by R.White (see edit history)

[Wheelmang]

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. 

[22touring]

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.

[Spinneyhill]

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.

[R.White]

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 May 10, 2018 by R.White (see edit history)

[Spinneyhill]

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.

[RichBad]

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?

[R.White]

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

[Spinneyhill]

I suppose one must also make sure the spark plugs don't reach down too far!

[R.White]

I know on Dodge 4 cylinder engines like mine the plugs are not over the valves.  They are also not over the pistons either which is a nuisance sometimes when it would be nice to be able to judge TDC.  Again the question of plug reach is probably more relevant on other engines.

 

Ray.

 

 

[Wheelmang]

Thank all for the help. As far clearance I don’t see how there will be an issue. Looks like you could shave at least .125 (not a typo) before any clearance concern. Hope to start this project in the next couple of weeks and will post pictures and progress. Thanks again for all the info.

Paul.

[R.White]

36 minutes ago, Wheelmang said:

Thank all for the help. As far clearance I don’t see how there will be an issue. Looks like you could shave at least .125 (not a typo) before any clearance concern. Hope to start this project in the next couple of weeks and will post pictures and progress. Thanks again for all the info.

Paul.

 

Hey Paul,  you need some metal left to keep the water in!?

 

Best of luck.

 

Ray.

[Wheelmang]

Finally started the rebuild that hopefully I can finish by September. WARNING - Nasty pictures follow along with a few questions.

I was ready to pull the engine (Surprisingly after only about 4 hours of dismantling. Gotta love the simplicity of these vehicles) and decided to do something unusual. I read the mechanics instruction manual. Can someone please confirm that in order to pull the engine I need to pull the transmission and in order to pull the transmission I need to drop the rear end? REALLY?  ?

As you can see the crank shaft is pretty much toast.

No gouging in the head although there were pieces of piston on top of the block. Did not see any damage to the top of the block.

The area in the block above the damage in the oil pan is slightly deformed and cracked. My welder friend says no problem fixing that.

The cylinder appears to be salvageable. The wall has no visible deep scores. Mostly what is seen in the picture is from where I wiped it down with a rag. I am guessing it will need at least .030 oversize. Guessing it will be best to take all four to the same size?  

How is the camshaft removed?  The instructions say something about a plug that requires a special tool. Also it needs to have .002 clearance? 

Thanks all for looking and commenting.

Paul

[R.White]

Yes, you do need to pull the rear axle back enough to drop the prop out of the torque tube (if you don't have an open prop) so you will have to drop the springs.  You will probably have to take out the battery box as well. Also the exhaust and the brake rods.  If you try to remove the engine from the gearbox in situ there is a risk that you will damage the clutch.  This is because the front cross member will not allow the engine to come out straight.  It will need to be tilted and an acute angle to clear it. 

 

The camshaft is located by a taper plug in the side of the block.  On 2 unit 6 volt cars this plug is hidden behind the generator.  Make up a simple puller.  It may be tight  but should just pull out.

 

It would be a false economy (in my opinion) to only bore one cylinder.  Get them all the same.  When you replace the con rods make sure they are modified to take fully floating gudgeon pins and cir clip retainers.  The original bolt clamping is probably the weakest design flaw in the engine and  has been the cause of many failures.

 

While you are getting the replacement crankshaft crack tested take the trouble to have the head and block crack tested too for peace of mind if nothing else.

 

Ray.

Edited May 22, 2018 by R.White (see edit history)

[Wheelmang]

Thanks Ray - always wise guidance!

[Wheelmang]

Got back to work today and dropped the rear end and tried to pull the trans. The cross member is unbolted and the trans is back far enough that the back of the engine is almost at the firewall. I cannot get the engine to separate from the trans. Any ideas anyone. Almost seems like the output from the crack is stuck in the pilot bearing.

[R.White]

Have you removed the two thin metal supports either side of the throw out bearing?  The clutch pedal needs to come off and throwout bearing fork lifted out. I found it easier to leave the clutch on the flywheel. Note how the clutch plates wear grooves into the pins. If you are trying to pull the clutch with the trans the clutch plates might be snagging on the pins.  Don't try to replace these by the way as the heat required to remove them can crack the flywheel.  I smoothed out the grooves and applied a little grease. 

 

Note there appears to be no means of lubricating the pilot bearing in the flywheel.  Mine was dry as a bone and caused clutch drag.  I replaced it with a sealed bearing. ( It is often the case that sealed bearings are lacking sufficient grease.  I would suggest you carefully prise off the cover and pack the bearing.  The cover should snap back into place)  Also renew the brass bushing in the end of the input shaft.  The trick for removing this is to tap in a thread and screw in a bolt .Use a puller or slide hammer. 

Edited May 30, 2018 by R.White (see edit history)

[Wheelmang]

Thanks Ray: "Have you removed the two thin metal supports either side of the throw out bearing?" I looked and looked but did not see anything else that could be removed. I presume these are accessed through the hole in the top of the bell housing? Thanks for the pics and info. 

Paul

[R.White]

Yes, looking in through the opening  there should be two square headed bolts.  remove these and the supports will slide off either side and you can lift out the throw out bearing fork.  

 

For future reference; when replacing them be careful not to drop them into the bell housing...  Don't ask me how I know this!!!?

 

Ray.

Edited May 30, 2018 by R.White (see edit history)

[Wheelmang]

Engine is out. Fat hands in a small place, broken cotter pins, frozen clutch pedal on shaft took four hours. So much for my simple comment earlier. Remainder of dismantle will likely be over the weekend. Just thinking that the throw out bearing may need replacing. (See video clip.)

I expected the bearing to slide off the output shaft but it appears it is pressed on?? Edited June 1, 2018 by Wheelmang
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[R.White]

Believe it or not, the throw out bearing on these clutches is supposed to move around...   I thought the same as you and ordered one only to find it was no different.  The throw out bearing is held in place by a large spring clip. Prise this off.. then the bearing unscrews.

 

Ray.

Edited June 1, 2018 by R.White (see edit history)

[MikeC5]

Good photos and information!  Thanks Ray.

[Wheelmang]

Amazing that that much movement is built in. Thanks for the post Ray - I was already trying to find a replacement.