The Stovebolt Site Forums The Shop Area Engine Shop 235 Starting RPM

I have a 1958 or 1959 235 that is about to go back in the truck. The engine turns over but seems cranking speed seems slow. Here are some specs:

1. 12 volt starter
2. 12.5 volts in 650 CCA battery
3. Cranking rpm 35-51 rpm using a hand held infared tach.
4. Engine seems to have good compression but have not pressure tested cylinders.

Does anyone know what the correct cranking speed should be on a stock 235?

Would a slow cranking speed indicate need for starter rebuild?

Cranking speed is not constant. The best I can describe change in cranking speed is that over multiple revolutions about 2/3's are in the 51 rpm range and 1/3 in the 31 rpm range on the digital handheld tach.

Thanks for any and all input.

Bob

Bob,

I don't know the correct cranking speed for a stock 235. I have had engines that barely turned over, but they would always catch and start.

If the engine is freshly rebuilt, it could be 'tight'..is yours a new rebuild?

A functioning starter shouldn't draw more than 250 amps at the most during a start with a good battery and mechanically sound engine. If you can find a current draw meter, it will help you pinpoint a bad starter.

The very first suspect would be the battery and cables. Many folks say they borrowed a good battery from a friend so it can't be the problem. This usually isn't the case! It must be fully charged and have clean posts and cables.

If the battery is proven to be good and it still turns over slowly, the starter would be the next item. The pregnant question is, does it start every time?

The state of charge of the battery is best checked with a hydrometer. A voltmeter will work too. Remember that all the cable connection points at the starter, frame and battery must be clean, shiny and tight.

Try the battery route first, then look at the starter. Many times you can disassemble the starter, install brushes, clean up the commutator and add a little oil to the bushings and it will make a world of difference.

If you have a voltmeter you can take a reading between the positive post and negative post of the battery while someone tries to start the engine. On a 12 volt system with a charged battery, the reading shouldn't go below 10 volts...if it does it indicates the starter is drawing too much current.

Stuart

Stuart: Thanks for your reply. I will try to fill in your questions:

1. I have never herd the engine start. I swapped a 350 for it several years ago. the is sealant compound around the head and block, oil pan etc. indicating it has been apart. Eng is clean and been stored inside for at least the last 3 years.

2. I used 10' heavy copper jumping cables from the battery to the starter, maybe 4 or 6 gauge but deffinately commercial grade. I am currently charging battery and when done will move it close to engine and use shorter cables since I have to get new ones anyway.

3. I can get an accurate battery voltage but amps would be a challange. Can I use a commercial grade antifreeze tester to get specific gravety? If not, I have a good Fluke digital multimeter. Is there a setting that will give me amps at both the battery and draw on starter?

4. The engine is out of the truck and I am not quite ready to put it back in yet. I have to finish the brake system and get a new wiring harness. I just pulled the engine out to bein the long term thinking and planning for that step.

Thanks,

Bob

First of all, scratch the jumper cables and use a pair of good-condition battery cables, 18" long or so. You just won't believe the amount of voltage drop in 10 feet of jumper cable!

Havr you tried to turn the engine by hand with the crankshaft center bolt, with the spark plugs removed? If it's stiff that way, it's not reasonable to expect the starter to wing it over. Take the plugs out, squirt some oil into the cylinders, and turn it by hand until any tight spots work out. It sounds like you've got a couple of rusty cylinders that are stalling the starter down. One that's been stored that long without a lot of special attention to make it airtight is almost bound to have some rust buildup in thre cylinders due to open valves and humidity getting in and out of a couple of cylinders. I always seal off all the intake and exhaust passages, and fill the cylinders with oil before any long-term storage.
Jerry

Bob,

Without some type of a shunt your multimeter will probably top out at 10 amps so that is a no-go! I wouldn't worry about doing much until I had the battery completely charged, in its box and attached with the proper cables to the installed engine.

I would for sure pull the plugs and squirt oil into the cylinders while all this other stuff was going on. If the engine has been in hibernation for that long it might have arthritis.

Trying to get good results using long jumper cables, a unknown battery and other jury rigged aperatus sometimes muddies the waters. When it's all together and wired properly it will probably be fine.

The only caveat I would have is..who did what to the engine that left goop hanging out of the gasket joints! This could be scary..meaning cinched down bearing caps or other makeshift repairs. I'm a pessimist though! Take your time and make the starting system right and I'll bet all will be fine.

While I don't know for sure, I don't think a hydrometer and a anti-freeze checker have anything in common other than appearance.

Stuart

Battery testers and antifreeze testers are both hydrometers, but they're calibrated differently. Sulfuric acid in a fully-charged battery will be somewhere between 1.250 and 1.265 specific gravity, depending on the manufacturers' specifications. All the cells should be approximately equal in acid concentration. Better-quality battreries usually have stronger acid. A discharged battery will have acid concentration down around 1.100 or less, as most of the acid has reacted with the plates to form lead sulfate. Recharging the battery increases the acid strength and reconstitutes the plates into lead (negative plate) and lead dioxide(positive plate). By measuring the acid strength, the state of charge is easy to figure out.

Jerry

Thanks to all for input.

I do have a batter hydrometer and after charging the battery I got the follow readings:

Voltage: 13.1
Specific gravety (all battery cells): between 1290 and 1300

I will measure and pick up proper length positive and negative battery cables tonight and try again.

Will report results tomorrow.

Thanks again.

Bob

The inductive (as sold by Snap-on; I'm sure that there are less-expensive ones available) or Hall-effect ammeters are used to measure the current drawn by the starter. As was mentioned, the current drawn with a 12-volt starter and battery should not be much above 200 amps.

Did you say how fast it cranks with the spark plugs removed?

Hoyt

OK, finally got 36" cables, 4 gauge. Using same batter, I now get approximately 99 rpm on the starting motor, almost double the speed as when I used the 10' jumper cables.

Does anyone know if approx 100 rpm on starter motor is normal?

Again, this engine is out of the truck and I am not trying to start it, just see if starter is ok and engine freed up.

Thanks,

Bob

I would say your goal has been reached if all you're trying to do is make sure the starter works and the engine turns over. I've never checked cranking rpms on my 235s, but 100 sounds reasonable.

Devin