Return to the Tool Shed Forum | Post a Follow-Up

 o
Thirty year old 4hp Briggs problem on shredder

Posted by ribertgropius VA (My Page) on
Wed, Jun 30, 10 at 10:10

I am trying to resurrect an early 1980's Kemp shredder with a 4hp Briggs engine. The shredder came to me with a blown head gasket and a tank full of old gas (ten years maybe?), and upon dissassembly I saw that one of the head bolts was deformed. I replaced the head gasket and bad bolt, torqued everything, drained the tank, and after fiddling around with it for an hour finally got it to start. It ran great for one hour, and I was impressed by the machine, and then died as if out of gas even though there was a third of a tank left.

Figuring that I had a carb problem, I dissassembled the carb, cleaned the orifices (didn't replace the diaphragm, yet), made sure the pick-up tubes and screens were clean, inspected the tank (no rust), and reassembled. Again, it took me about an hour to get it started, and then it ran for an hour and again died like it was out of gas.

This engine has a very simple control arrangement: the only speed control is the governor, which exerts force against a spring to close the throttle if it over revs. I put a mini-tach on it just to verify engine speed and it was right around 3400 rpm which is where it is supposed to be according to the specs on the engine and the shredder.

I re-built the carb completely, replacing the diaphragm and needle valve. I double checked the fuel pick-up tubes to make sure there was proper seal at their bases, since the long fuel pick-up tube was loose when I dissassembled it, replaced the gaskets, reassembled...and NOTHING. I have good spark. The fuel cup in the tank is full of gas. I tried spraying starting fluid into the carb, and it doesn't even catch. I tried pouring a thimble full of gas in the carb and again, no luck.

I am beginning to think I have a compression problem. Will an engine run fine with bad compression but not start? The head looked very clean when I took it off, as if someone had previously cleaned it, and the valves "looked" good but I didn't have a way to really check them then. I have a leak-down tester and am going to try it to see if I can hear a leak in the cylinder.

If it is a compression problem, is it worth fixing? I have less than $40 into the machine between head gasket, carb kit, new plug, oil, and carb cleaner. I could buy a new 6.5 hp engine from Harbor Freight on sale for about $115, but I hate to throw this one away if it is serviceable. How difficult is it to replace a valve on one of these?

Thanks for the advice.


Follow-Up Postings:

 o
RE: Thirty year old 4hp Briggs problem on shredder

  • Posted by baymee LehighValleyPA (My Page) on
    Wed, Jun 30, 10 at 11:26

I'm sure the 4HP engine is built 10 times better than the engine from HF. So, I would work on your problem first. You don't say the condition of the spark plug, is it black? sooty?

An engine with poor compression might start, but it doesn't come to full RPM as quickly as a good engine. Any compression below 60 is going to be very hard to start. 90+ is preferred.

Do your leakdown test first.


 o
RE: Thirty year old 4hp Briggs problem on shredder

The plug looked great, not sooty at all. And when it did start, yes, it took a while to get it up to full speed but it seemed to run fine then. The only thing that seemed strange to me is that in tuning the carb the engine seemed to run best with the needle only 1/2 turn open (quite a bit different than the 1-1/2 turns recommended for initial start). I assumed that the needle and seat might be worn so I have replaced it since, but I have not had it running with the new needle yet.

Initially I thought I had a fuel problem which is why I spent so much time on the carb, checking for leaks, cleaning everything, re-sealing the pick-up tubes at their base, making sure that the screens were not clogged. I don't think this engine has alot of wear on it from appearance, but I have no history on it. And the fact that the head was almost pristine makes me think that someone tried to do this repair once before and then perhaps gave up? Not sure, but what I do know is that I have had it running twice and once running, it seemed to have adequate power.

The way the machine is set up is that it drives a centrifugal clutch that engages the pulley that drives the chipper axle via belt. I have noticed that the clutch does seem to engage slightly even when pulling the starter, so the engine does encounter a little drag. I removed the clutch cover and made sure everything spins freely, but there must be just enough friction to catch a little. On the other hand, the clutch is driving an axle that has alot of weight on it so that it provides a fair amount of centrifugal force almost like a flywheel to help it keep turning when I pull the starter cord.

This engine appears to have been built around 1981. I don't think it has a compression release so I will do both the compression test and leak down test. I hate throwing things away...


 o
RE: Thirty year old 4hp Briggs problem on shredder

The plug looked great, not sooty at all. And when it did start, yes, it took a while to get it up to full speed but it seemed to run fine then. The only thing that seemed strange to me is that in tuning the carb the engine seemed to run best with the needle only 1/2 turn open (quite a bit different than the 1-1/2 turns recommended for initial start). I assumed that the needle and seat might be worn so I have replaced it since, but I have not had it running with the new needle yet.

Initially I thought I had a fuel problem which is why I spent so much time on the carb, checking for leaks, cleaning everything, re-sealing the pick-up tubes at their base, making sure that the screens were not clogged. I don't think this engine has alot of wear on it from appearance, but I have no history on it. And the fact that the head was almost pristine makes me think that someone tried to do this repair once before and then perhaps gave up? Not sure, but what I do know is that I have had it running twice and once running, it seemed to have adequate power.

The way the machine is set up is that it drives a centrifugal clutch that engages the pulley that drives the chipper axle via belt. I have noticed that the clutch does seem to engage slightly even when pulling the starter, so the engine does encounter a little drag. I removed the clutch cover and made sure everything spins freely, but there must be just enough friction to catch a little. On the other hand, the clutch is driving an axle that has alot of weight on it so that it provides a fair amount of centrifugal force almost like a flywheel to help it keep turning when I pull the starter cord.

This engine appears to have been built around 1981. I don't think it has a compression release so I will do both the compression test and leak down test. I hate throwing things away...


 o
RE: Thirty year old 4hp Briggs problem on shredder

I did a leadown test that revealed that the intake valve was leaking. I opened the valve spring access cover and found no clearance on the intake valve, while the exhaust had .006. I pulled the head off and removed the springs, and I could turn the intake valve by hand with no friction against the seat as I pressed on it. So grinding the end off should help it seat properly. Am I correct in thinking it should also have about .006 clearance? In comparison, if I spun the exhaust valve I could feel it rubbing against its seat.

The valve and seat looked great with even margins, BUT...the steel intake valve seat insert is loose, and comes out freely. I researched on line and found out that these mid-1980 engines often have this problem, and have read everything from "you can't fix it" to "use green loctite" to "peen the edges around it once installed to hold it in place." Anyone have any experience with this problem and successful fixes? Stems looked fine and came out freely.

Clearly the lack of clearance was contributing to the compression problem, and the loose seat may have something to do with the irregular readings. I need to fix both problems.

Thanks for the advice and encouragement.

Robert


 o
RE: Thirty year old 4hp Briggs problem on shredder

  • Posted by canguy British Columbia (My Page) on
    Fri, Jul 2, 10 at 0:09

You should have .005-.007 intake and .009-.011 exhaust lash.If the seat has come loose the engine has been overheated. Stake the seat with a center punch at three points 180 degrees apart then peen the surrounding metal with a flat punch.As long as the cylinder is not scored or excessively worn you should be o.k.Replace the valves if the faces are worn or burnt.


 o
RE: Thirty year old 4hp Briggs problem on shredder

  • Posted by baymee LehighValleyPA (My Page) on
    Fri, Jul 2, 10 at 6:19

Here is a link to a good discussion on this loose valve seat issue. Scroll down towards the bottom.

http://forums2.gardenweb.com/forums/load/tractor/msg062001491527.html?26


 o
RE: Thirty year old 4hp Briggs problem on shredder

SO.....

It is now back together and running, starting in just a couple of pulls!

But...instead of peening the seat back in place, which certainly sounds like the correct repair, I opted for now to try the green loctite to secure it in place. I applied the compound, let it dry, and then lapped both valves.

The reason I opted to not peen the seat at this point is that in reading about the process it sounded like there was a fairly good chance that I might slightly move the seat, which then would require re-cutting the seat for its now position. If my repair doesn't hold I will use the peening method with the valve in place to hold the seat from moving, and then lap the valves again. I checked around to see if someone locally would do the peening repair at a shop, and one shop said sure, but it would be about $70, and another said they wouldn't do it because they haven't had good luck with the repair holding.

I also may want to open the head up again in the near future anyways. In doing my repair, I ground more off the intake valve stem than I wanted (first it was too little, and the second time, I pressed on the valve as I did and...well..OOPs). So I probably should try to buy an intake valve and replace it, and when I do I will inspect the seat to see how it is doing.

In hindsight, it appears that almost all of my problems were compression related. I should have paid more attention to the fact it didn't catch even with starter fluid, nor when I poured a little gas in the carb. The fact I had to lean out the mixture to less than 1/2 turn out also should have suggested that the mixture was off for the cylinder (which it did, but I thought it was a supply issue when in fact it was a low compression issue).

Now that the intake valve is closing properly, the engine starts right up at 1 1/2 turns and required just a little adjustment to 1 1/4 turn for optimum response. The maintenance I did on the carb certainly didn't hurt, but it does show the limits of an amateur such as myself in having to find out things the hard way. On the other hand, I learned alot in the process.

Thank you to everyone for their advice. I will keep that peening diagram for the future since I suspect I will need it!

Robert


 o Post a Follow-Up

Please Note: Only registered members are able to post messages to this forum.

    If you are a member, please log in.

    If you aren't yet a member, join now!


Return to the Tool Shed Forum

Information about Posting

  • You must be logged in to post a message. Once you are logged in, a posting window will appear at the bottom of the messages. If you are not a member, please register for an account.
  • Please review our Rules of Play before posting.
  • Posting is a two-step process. Once you have composed your message, you will be taken to the preview page. You will then have a chance to review your post, make changes and upload photos.
  • After posting your message, you may need to refresh the forum page in order to see it.
  • Before posting copyrighted material, please read about Copyright and Fair Use.
  • We have a strict no-advertising policy!
  • If you would like to practice posting or uploading photos, please visit our Test forum.
  • If you need assistance, please Contact Us and we will be happy to help.


Learn more about in-text links on this page here