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Stihl BR 500 blower with low compression 60 psi

#1

S

sinful619

Hi,

I'm trying to help out a relative with a Stihl BR 500 blower that won't start. Fuel and spark seem okay. Compression is at 60 psi which seems low to me. I also noticed it has two valves as if it was a 4 stroke but it uses premix like a 2 stroke. What's the right approach here?

thanks !


#2

I

ILENGINE

Sounds like the Stihl 4-Mix engine. Its 4 stroke but uses 2 stroke oil for lube. 60 is way low, and probably won't start or run at that compression.


#3

Rokon

Rokon

4-mix engines have valves. It is also possible that a piece of carbon is holding a valve in the slightly open position. Either way 60#'s of compression won't run these two strokes.


#4

S

sinful619

Okay so it's probably time to take it apart and find out what the deal is.


#5

Ric

Ric

sinful619 said:
Hi,

I'm trying to help out a relative with a Stihl BR 500 blower that won't start. Fuel and spark seem okay. Compression is at 60 psi which seems low to me. I also noticed it has two valves as if it was a 4 stroke but it uses premix like a 2 stroke. What's the right approach here?

thanks !
Click to expand...

sinful619 said:
Okay so it's probably time to take it apart and find out what the deal is.
Click to expand...


Like everyone else says it's a 4 mix engine, a single cylinder four stroke engine that runs on a gasoil lubrication. How old a unit is the BR 500. I ask because if you have Fuel and Spark it could be something as simple as the spark arresting screen in the muffler needing to be clean, if that screen is plugged it will not start or if it does it wont have any power.


#6

S

sinful619

it's two yrs old and they use it a lot..commercial use. I'm trying to see if the 60 psi compression reading is relevant to this particular blower with four stroke technology/2 valve. I need someone to confirm that before taking apart.


#7

S

sinful619

I've read somewhere not to rely on a compression test for this particular 4 stroke blower. Stating the compression increase once the engine warms up. I'm confused.

spark arresting screen is clean btw.


#8

Ric

Ric

sinful619 said:
I've read somewhere not to rely on a compression test for this particular 4 stroke blower. Stating the compression increase once the engine warms up. I'm confused.

spark arresting screen is clean btw.
Click to expand...

Are you getting anything at all when you try to start the blower, is it turning over or acting like it wants to start or is it just flat?


#9

A

angellonewolf

sinful619 said:
Hi,

I'm trying to help out a relative with a Stihl BR 500 blower that won't start. Fuel and spark seem okay. Compression is at 60 psi which seems low to me. I also noticed it has two valves as if it was a 4 stroke but it uses premix like a 2 stroke. What's the right approach here?

thanks !
Click to expand...

i think i am right in saying you need more than 70 psi for it to work and that still not run as it should but please some one on here will confirm if i am right i think i seen this some where on the net

i would first try about 3ml of fresh fuel open the choke tip the unit on its side pull the throttle and drop the fuel right in there so it goes in to the chamber (you will have to take the air filter out first) close the choke so it full on and try starting it its should start fairly easily if its starts it prob is worth playing with if it dont and you know the psi is low then sell it for spares they do go fairly well even not starting

if it starts and runs for 2/3 secs then you have to decide if it needs more than a strip down carb cleaner and an air compesser( do not get the carb cleaner on the rubbers as it will rot them) or if your in usa prob better to but new carb as have seen they sell cheap there if your in uk you might want to take a seat before ring for a price its about £90 for a carb a new sthil is only £150 lol

hope this helps but there will be someone hear with more know how than me thanks angel


#10

T

tybilly

when I went to a stihl service school back in 99,lol...they could've cared less about compression testing,they wanted a crankcase vacuum/ pressure test,..after I checked the spark arrestor screen,id pull the muffler and carb and check the condition of the cylinder wall, and piston if a ball pont pen cant feel any scratches neither can the ring, hope that helps


#11

EngineMan

EngineMan

Are you doing the test with the throttle full open..?


#12

S

stumpfg

valve adjustment is very important. I think it is .002 for both vavles


#13

S

sinful619

Ric said:
Are you getting anything at all when you try to start the blower, is it turning over or acting like it wants to start or is it just flat?
Click to expand...

Completely flat.

angellonewolf said:
i think i am right in saying you need more than 70 psi for it to work and that still not run as it should but please some one on here will confirm if i am right i think i seen this some where on the net

i would first try about 3ml of fresh fuel open the choke tip the unit on its side pull the throttle and drop the fuel right in there so it goes in to the chamber (you will have to take the air filter out first) close the choke so it full on and try starting it its should start fairly easily if its starts it prob is worth playing with if it dont and you know the psi is low then sell it for spares they do go fairly well even not starting

if it starts and runs for 2/3 secs then you have to decide if it needs more than a strip down carb cleaner and an air compesser( do not get the carb cleaner on the rubbers as it will rot them) or if your in usa prob better to but new carb as have seen they sell cheap there if your in uk you might want to take a seat before ring for a price its about ｣90 for a carb a new sthil is only ｣150 lol

hope this helps but there will be someone hear with more know how than me thanks angel
Click to expand...

I have not try to poure fuel directly in the carb. might be the next thing although the entire blower is taken apart now with the exception of the engine against the plastic shield/fan. I can't take the fan bolt off but just found out a piston stop tool is necessary.

tybilly said:
when I went to a stihl service school back in 99,lol...they could've cared less about compression testing,they wanted a crankcase vacuum/ pressure test,..after I checked the spark arrestor screen,id pull the muffler and carb and check the condition of the cylinder wall, and piston if a ball pont pen cant feel any scratches neither can the ring, hope that helps
Click to expand...

yes but I still need to know what the 60 psi reading is and why.

EngineMan said:
Are you doing the test with the throttle full open..?
Click to expand...

Yes with the throttle wide open.

stumpfg said:
valve adjustment is very important. I think it is .002 for both vavles
Click to expand...

I adjusted the valves differently for testing purpose: first tighetened both to 1/4 turn and did a compression test with 30-35 psi result. then went back to the original position and got back 60psi. loosened the valves this time 1/4 turn and got the same 60 psi result (valves pretty loose at this point).

I don't have a thin enough feeler gauge so that's the method used so far to see if the compression would change.


I'm really lost here.


#14

Rokon

Rokon

sinful619 said:
I don't have a thin enough feeler gauge so that's the method used so far to see if the compression would change.


I'm really lost here.
Click to expand...

You need a special feeler gauge, Stihl was very crafty in their engineering.

You backed the valve lash off till the rockers are loose, and still have 60 PSI? Doesn't sound good.

By your descriptions I am leaning towards a scored cylinder.


#15

T

taxidermist

Dont worry about compression as they have a compression relief and you will not get a good reading. Always do a leak down test to make sure valves are sealing. You can get the feeler gauge at a dealer for $.50

I have a 4 mix that is also a no start and I have tried a good carb, cleaned the valves, lashed the valves. I have been told that there was a problem with the ing module so I will try that next.

I am not really a parts replacer but this one has me stumped!

Rob


#16

S

sinful619

Hi all,

I have not been able to remove the fan bolt without the piston stop tool. I tried using the small rope method inside the cylinder and is not working for me.

No leak down tool here. Do you recommend any? do an automotive leak down tool work for a small engine? And have you've try to get compression reading just to see where it's at?


#17

S

sinful619

after taking the motor apart the problem seems to be carbon build up on the exhaust valve and seat. I just finished cleaned everything up and used some lapping gel to properly seat the valves again.

I'm placing everything back together and not sure how the ring gaps should face...this piston doesn't have dowels for the ring gaps.


#18

EngineMan

EngineMan

This should help you out.

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#19

S

sinful619

ah nice thanks it says 120 degrees but I didn't think about getting a reply so went to 180 degrees instead of 120 and engine is all sealed up now. you think those 60 degrees off might give problems? On this cylinder the ring end gaps don't pass through intake or exhaust ports.

My next step is doing the valve adjusment..


#20

T

taxidermist

taxidermist said:
Dont worry about compression as they have a compression relief and you will not get a good reading. Always do a leak down test to make sure valves are sealing. You can get the feeler gauge at a dealer for $.50

I have a 4 mix that is also a no start and I have tried a good carb, cleaned the valves, lashed the valves. I have been told that there was a problem with the ing module so I will try that next.

I am not really a parts replacer but this one has me stumped!

Rob
Click to expand...

Fixed mine!

http://www.lawnmowerforum.com/stihl-forum/18987-stihl-tech-help-110-r-4-mix.html


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