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Model 28 Vertical - No Compression

#1

H

Humbug

Hi All,

I was using my Etesia Bahia Mower today when there was a loud bang from the engine (I think, I had my ear defenders on) and it quit running. I tried the starter but it sounded like there was no ignition and the engine was turning over much more easily than normal. I pulled the spark plug and screwed in my compression tester, when I turned it over the compression was zero.

The engine is a B&S 28M707-1187-E1, vertical 4 stroke, 13HP Diamond I/C.

Could the complete lack of compression be caused by a blown head gasket or is it possibly something more serious? I can't see any oil leaking from it which makes me think that perhaps it isn't the gasket but I'm a bit of a novice when it comes to engine repair. That said, I'm not afraid to get stuck in and get my hands dirty.

Thanks in advance for any advice,
Paul.


#2

StarTech

StarTech

Could be as simple as the valve clearance have gone to zero with old L-head engine. Or worst a broken connecting rod. Remove the spark plug and check for piston movement.


#3

B

Bertrrr

Stick a small rod in the spark plug hole and roll it slowly and make sure the piston is moving up and down , if you threw a rod it will not be moving and if that's the case you needn't worry about a rebuild , just replace the engine or mower itself


#4

H

Humbug

Thanks for the ideas guys. I tried putting a rod in the spark plug hole and turning the flywheel, there was no piston movement at all so I figured it was probably the con rod that had broke. I decided to pull the engine out of the mower to take a look, thankfully it was pretty easy to remove. I got it on the bench and removed the head. When I turned the flywheel the valves are both opening and closing as they should but the piston was stuck at the top of it's stroke. There was just enough of the piston exposed to gently grip it and pull it out of the cylinder. Sure enough the con rod had exploded at the big end and there was a lot of debris in there.

I looked for a replacement engine on Ebay and managed to find an identical one but it was $$$$. Given that I've got this far with it would it be fairly straightforward to replace the broken rod? If I go ahead with the repair I'm guessing that I'll need to replace the head and case gaskets, should I replace any others while I've got it stripped down? I guess I'll also need to remove the flywheel to open the case, any suggestions on how best to pull it?


#5

Tiger Small Engine

Tiger Small Engine

Humbug said:
Thanks for the ideas guys. I tried putting a rod in the spark plug hole and turning the flywheel, there was no piston movement at all so I figured it was probably the con rod that had broke. I decided to pull the engine out of the mower to take a look, thankfully it was pretty easy to remove. I got it on the bench and removed the head. When I turned the flywheel the valves are both opening and closing as they should but the piston was stuck at the top of it's stroke. There was just enough of the piston exposed to gently grip it and pull it out of the cylinder. Sure enough the con rod had exploded at the big end and there was a lot of debris in there.

I looked for a replacement engine on Ebay and managed to find an identical one but it was $$$$. Given that I've got this far with it would it be fairly straightforward to replace the broken rod? If I go ahead with the repair I'm guessing that I'll need to replace the head and case gaskets, should I replace any others while I've got it stripped down? I guess I'll also need to remove the flywheel to open the case, any suggestions on how best to pull it?
Click to expand...
Did you run low on oil, or out?
Did engine overheat? Pull engine shroud and check top of engine and cooling fins for oil, dirt, and debris and remove as necessary.
What year and how many hours?

Once you open up the engine, you can determine what needs to be replaced. Check crankshaft for scoring and wrist pin. Check condition of piston, rings, and cylinder. Depending on hours and condition, it may just need a new connecting rod, gaskets, etc.


#6

B

Bertrrr

Make sure your crankcase isn't damaged.
Valves maybe bent and head could be scored up too


#7

H

Humbug

Tiger Small Engine said:
Did you run low on oil, or out?
Did engine overheat? Pull engine shroud and check top of engine and cooling fins for oil, dirt, and debris and remove as necessary.
What year and how many hours?

Once you open up the engine, you can determine what needs to be replaced. Check crankshaft for scoring and wrist pin. Check condition of piston, rings, and cylinder. Depending on hours and condition, it may just need a new connecting rod, gaskets, etc.
Click to expand...
I think that the oil level was OK as I had only renewed it 3-4 months ago. I was mowing grass that was probably too long and wet . The mower bogged down a couple of times and I should have known to leave it but I thought I would just take about a third of a stripe at a time and all would be ok, clearly it wasn't! :oops:

I have the engine fully stripped down now and I have cleaned it up (although it wasn't too scruffy). Inside the case was a whole load of debris, it was like a box of grit! I cleaned it all up and and can see that there is some damage to the inside of the case but it isn't punched right through. Is the crank case under high pressure when the engine is running? Might I get away with it?

The cylinder looks really clean, as do the rings and piston but there is some scoring on the crank shaft, could that be carefully ground/polished out? The wrist pin is fine.

The mower is about 20 years old but it's in great condition generally. I think it was used commercially before I bought it - I hope that means it was well maintained. I've had it almost 5 years and it has been really solid.


#8

H

Humbug

Bertrrr said:
Make sure your crankcase isn't damaged.
Valves maybe bent and head could be scored up too
Click to expand...
There is a little damage to the inside of the case but it isn't punched through. The valves appear to be OK. When I rotate the camshaft the valves appear to open and close smoothly. I cleaned the head up and it looks to be completely intact. Just some scoring to the crankshaft. :(


#9

B

Bertrrr

Looks like you got lucky - a new rod might just be all you need along with gaskets etc.


#10

H

Humbug

I’m making some progress with rebuilding my engine. I have ordered a gasket set and a new con rod. In the new gasket set there are 5 crankcase gaskets, 3 black, 1 brown and one light grey. Do I need to use them all? And if so, in what order should I stack them?


#11

B

Bertrrr

If they're all the same you got some spares , you don't need more than one, Sometimes they'll put several different types to fit a various assortment of engines


#12

H

Humbug

Bertrrr said:
If they're all the same you got some spares , you don't need more than one, Sometimes they'll put several different types to fit a various assortment of engines
Click to expand...
They all appear to be identical but I'll have a closer look at them and see if there are any small differences between them, could they be different thicknesses?. If they are all the same is there any preference about which type to use?


#13

B

Bertrrr

I always use Permatex Gasket sealer on one side , Don't put anything on it until you are ready to put the 2 halves together, Use sealer or whatever you like only on one side in case you need to take it apart again , the gasket will hold and you should be able to re use it not having to scrape it off the clean side - never ran across any gaskets for a small gas engine crankcase with varied thickness . Just make sure it covers all the contact surfaces and does not cover any ports for lubrication or vents etc.


#14

B

bertsmobile1

The different colours are different thicknesses
You do a dry assembly ( all gaskets fitted ) then measure the end float of the crankshaft then remove enough of them to get the specified end float .
I am at the other computer so do not have the specs but from memory it is around 0.002"


#15

H

Humbug

bertsmobile1 said:
The different colours are different thicknesses
You do a dry assembly ( all gaskets fitted ) then measure the end float of the crankshaft then remove enough of them to get the specified end float .
I am at the other computer so do not have the specs but from memory it is around 0.002"
Click to expand...
That makes sense. I’ll go and dig out my dial indicator. A quick search seems to suggest that anywhere between 2 and 30 thou is acceptable but I’ll have a look for the specs on my engine to be sure. 😎


#16

H

Humbug

Thanks to the great help from you guys I’m almost done rebuilding this engine. I just have one last question though. It’s been a couple weeks since I took this apart and I can’t remember where one of the springs hooks onto. 😳

The spring that has me baffled is the super-thin wire spring that’s wrapped around the regulator link rod. At the regulator lever end I have it hooked in but I can’t remember where it hooks to at the carburettor end.

In the picture it’s in the top right corner. Anyone know this engine or have a diagram please?

Attachments





#17

B

Bertrrr

Usually a tiny hole right on the same lever the larger rod fits onto .


#18

H

Humbug

Bertrrr said:
Usually a tiny hole right on the same lever the larger rod fits onto .
Click to expand...
Perfect, many thanks 😁. I couldn’t see it so I pulled off the air filter housing base and it was much easier to see. I’m much obliged to you sir.


#19

H

Humbug

I had the engine back in one piece and fitted back in the mower but I just couldn’t get the thing to fire 🤬.

I’m kicking myself for not checking it before I re-fitted the engine but I can only get about 20PSI of compression out of her. I replaced the head gasket and cleaned the valves (I didn’t grind or polish the seats), I didn’t touch the rings as they seemed to be fine. Is it likely to be the valves that is causing the loss of compression? I can’t think what else it could be.

This morning I pulled the engine out again and checked to see if I had got the rings offset from each other. They looked reasonable when I pulled the piston out but I ensured that they were 120 deg to each other when replacing it. The valves and pushers all seemed ok. I’m really baffled now. I’d be really grateful for any suggestions please.


#20

B

bertsmobile1

This is why we do leak down tests
Lock the engine at TDC Firing stroke so both vales are closed
Remove spark plug and wrap some cloth around a long air duster
Remove dip stick
Insert into the spark plug hole & blow air into the cylinder ( low pressure )
Listen at the dip stick tube , cab & muffler .
You should get a SMALL amount coming from the dip stick and none from the muffler or carb
Spray around the gasket with soapy water and check for air bubbles


#21

Tiger Small Engine

Tiger Small Engine

bertsmobile1 said:
This is why we do leak down tests
Lock the engine at TDC Firing stroke so both vales are closed
Remove spark plug and wrap some cloth around a long air duster
Remove dip stick
Insert into the spark plug hole & blow air into the cylinder ( low pressure )
Listen at the dip stick tube , cab & muffler .
You should get a SMALL amount coming from the dip stick and none from the muffler or carb
Spray around the gasket with soapy water and check for air bubbles
Click to expand...
A mistake was probably made during assembly.


#22

H

Humbug

bertsmobile1 said:
This is why we do leak down tests
Lock the engine at TDC Firing stroke so both vales are closed
Remove spark plug and wrap some cloth around a long air duster
Remove dip stick
Insert into the spark plug hole & blow air into the cylinder ( low pressure )
Listen at the dip stick tube , cab & muffler .
You should get a SMALL amount coming from the dip stick and none from the muffler or carb
Spray around the gasket with soapy water and check for air bubbles
Click to expand...
Thanks for the great advice. I did as you said and applied low pressure air in through the spark plug hole with the piston at TDC. I had the exhaust removed and could feel that air was leaking through the exhaust valve. I pulled the head off again and shone a bright light in through the exhaust port. Sure enough I could see a sliver of light around the exhaust valve. I haven’t checked the inlet valve yet.

The engine ran ok before the broken con rod so either I’ve done something wrong in the reassembly or the con rod incident damaged something else if the valve(s) now won’t close.

You can probably tell that I’m a real novice at this but I’m having fun and learning along the way.


#23

B

bertsmobile1

Exhaust vales run yellow hot which is well into the forging temperatures
If the piston touched it when running then the head is most likely bent with respect to the shaft .
Good thing is B & S valves are cheap
Simple test is to pull the head, remove the valve spring and rotate the valve by hand looking for wobble in the valve head .


#24

H

Humbug

bertsmobile1 said:
Exhaust vales run yellow hot which is well into the forging temperatures
If the piston touched it when running then the head is most likely bent with respect to the shaft .
Good thing is B & S valves are cheap
Simple test is to pull the head, remove the valve spring and rotate the valve by hand looking for wobble in the valve head .
Click to expand...
Thanks for that. Is this for an OHV engine? Mine has side valves. 🙂

I’ve been having a closer look at it this morning and when the piston is at TDC I can see an even gap right around both valves. When the exhaust valve opens the intake valve actually appears to close fully and vice versa. Would this point to a damaged cam shaft?


#25

B

bertsmobile1

Because of the nature of the gas flow in SV engines, the valve seat burns / erodes over time
The effect of this is the valve then can not close fully and the fix is to remove a few thou off the end of the exhaust valve
The B & S L Head manual has full instructions on how to do this
When I do them I set the lash at the maximum amount ( some times even a bit more ) .
Sorry about the red herring my fault for not checking the details properly first
The other thing that happens with side valve engines is bits of carbon often get caught under the exhaust valve preventing the valve from fully closing


#26

H

Humbug

bertsmobile1 said:
Because of the nature of the gas flow in SV engines, the valve seat burns / erodes over time
The effect of this is the valve then can not close fully and the fix is to remove a few thou off the end of the exhaust valve
The B & S L Head manual has full instructions on how to do this
When I do them I set the lash at the maximum amount ( some times even a bit more ) .
Sorry about the red herring my fault for not checking the details properly first
The other thing that happens with side valve engines is bits of carbon often get caught under the exhaust valve preventing the valve from fully closing
Click to expand...
No need to apologise, I appreciate anyone taking the time to offer help 😊.

I tried grinding about 7 thou off the end of both valves and when I checked again I couldn't see any light around the valve seat. I reassembled the engine and did a compression test - it had risen from 20psi to over 90psi! I dropped the engine into the mower and hooked everything back up and she fired straight back into life again. I was so happy :D.

I let the engine run for a few minutes then took it for a spin around the garden. It seems to be a little down on power, the idle is low and it struggled with a hot restart. I didn't make any modifications to the carb when working on the engine, I just removed it as a single unit and reinstalled it again. Is it likely that I'll need to tweak the carb settings to get her running smoothly again?


#27

B

bertsmobile1

(y) :giggle:


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