CakeBandit

CakeBandit

Active Member
I have been having soot in the carb, with dieseling when shutting down. Carb is Zenith.
Took it apart, lapped it again, changed the pin for the float (new) and readjusted the float for a nylon (31mm?) , cleaned the soot out. Adjusted the tappets. Did a compression test with cold engine with plugs in except for the one I was testing. I know its the wrong way to test. The results:
1) 34, 37, 40
2) 110
3) 100
4) 105
I read that it should be around 145psi.
I put #1 to TDC and did air test for that cylinder, and the air is coming out of the exhaust. When pulling the plug on #1 while running its barley noticeable.
My question is does the vacuum gauge in the video also support the theory that I have trouble with exhaust valve/seat in #1 cyl? Or do I also have head gasket trouble as well?

https://files.catbox.moe/ru0za4.webm

I need to drive it for a couple hours away before I can pull the head and I don't even know what parts to change while I have the head off besides new exhaust valve seat and valve. Its 7:1 compression.
 
If the engine has been run on unleaded without the additive for a significant period, the exhaust valve and its seating may have burnt out. If this is the case, expect so.e damage to the other exhaust valves and seats. The head may need machining to accept new valve seats.

Col
 
Are you sure #1 was on its compression stroke? Are the tappets adjusted properly?
The valve seat could well be burnt too, if you've never had new seats in
 
I suspect it is fouled with carbon build up. Now that I think about it I just assumed it was on compression stroke, I looked at the notch on the pully, so I guess I need to pressure check again as it might have been finishing with exhaust. doh lol

So I can just buy some hardened seats and have a machine shop press them in? I have took the head off twice, the last time was 7 years ago I think, my brother inlaw took the head to a machinist and he put new seats in, I think they were machined from stock material after they sized them up. Tappets are correct .010 following the manual.
 
A machine shop can fit seats, but they aren't just a press fit, they are machined in place then the valves ground in to match
If it's dieseling then compression isn't the problem, like you say it's the following embers of carbon igniting the fuel
 
I bought a 2nd hand head to have it converted for unleaded fuel. It had obviously been run on unleaded fuel for quite a time as all the valve seats were in very poor condition. Even the inlet valve seats were pitted. Its only a thought but from your description of the condition of the carb could it be a faulty inlet valve/seat leaking on combustion. Seven years ago is not a long time for new seats to be worn did you fit new valve guides at that time, if not l would this time, they are very cheap in comparison to all the work.
 
yes the machine shop did all that, I just meant I think they took some stock and put it on a lathe to size it, press it in and then cut the angle I assume, anywayz I'll plan on buying a hardend set of seats on fleabay along with valve guides in the future. I replaced the tappet adjusting screws a few years back and the ones I pulled out were extremely worn down, I just wonder what parts I should replace with the head off. So far on my list then its valve seats, valves and valve guides. I only have a about 4 months a year of free time and parts can take 3 weeks to get to me. Thanks for the replies so far.
 
So far on my list then its valve seats, valves and valve guides. I only have a about 4 months a year of free time and parts can take 3 weeks to get to me.

If you consider the Head to be your issue then add springs to your list to be certain. I'm sure there was a post on here way back where someone tested each cylinder with both valves shut with compressed air which seems a great idea as if valves are being the issue airflow may be found through either of the manifolds
 
good article on vacuum gauges here https://www.motor.com/magazinepdfs/...alve and right at the intakeand exhaust ports.

Mine was similar but not so bad on compressions and i found this. i had local workshop fit hardened seats and one new valve now all good.
IMG_20220308_210804.jpg
 
I ordered parts from Turner engineering in the UK. Hardened valve seats is one of the items. Anybody fit these themselves? I am not sure if I trust the machine shop in my neck of the woods. All I need is a boring head on a pillar drill press right? I don't have either but have access to a drill press and would just need to buy the carbide bits for the cutting head. Hoping someone here could give me a pointer. I have a gauge and micrometers and a large oven to heat the head up. I have not double checked the book but the valve guide inner dia. is 11/32" I think, Can I just put some round bar stock 11/32" into the bottom of a boring chuck as pilot? Or am I in over my head, This is new to me.

I will probably be taking the head off in a couple days and will post what I find for entertainment. :) I didn't order springs, sorry, but just about every other item for the top end.
 
I would trust a machine shop more than i trust myself as i don't have the machine to do it. How would you even begin to machine out the space for the hardened seats??
 
kermit_rr said:
I would trust a machine shop more than i trust myself as i don't have the machine to do it. How would you even begin to machine out the space for the hardened seats??
Click to expand...
I'm on the fence still, not even sure if I have inserts already in there from a few years ago or if they just recut the seats a bit more. I was thinking of purchasing a boring head to use on a drill press. Then putting head in oven to 150c and take out hardend seats from fridge and either press or hammer them in. I'm just as nervous as you. lol I think I can do it if I stay sober, measure 3 times and be patient when cutting. I was thinking of cutting a valve stem to use as a pilot to get (almost) dead center with boring mill tool.

I'm located in Asia a upcountry farm village, the machine shop that services all the backyard mechanics (mostly newer diesels) is lets just say like someone who hordes stuff in their house. Big press, big lathe and big old drill all surrounded by engine parts every which way. Maybe I'll head over there and ask them what they think.
 
The machine to be used needs to be very precise. Most pillar drills wouldnt have the required tolerance in the shaft bearings for such a job. Even the slightest lateral slack in the bearings would cause the cut to be oversized.

Col
 
Colthebrummie said:
The machine to be used needs to be very precise. Most pillar drills wouldnt have the required tolerance in the shaft bearings for such a job. Even the slightest lateral slack in the bearings would cause the cut to be oversized.

Col
Click to expand...
Okay, thanks for that info. I'm leaning on having the local machine shop do them if those are not hardened seats already pushed in the pictures.

I did pull the head off today. I was right on with my diagnosis which I am happy, Intake [Edit]: Exhaust valve #1. The reason the valve is oval shaped I still don't know. It look like a coolant passage or two is completely blocked between #1 and #2 cylinder. I am going to post pictures, could somebody tell me what the discoloration is in the cylinder wall? I think I may have had a close call with overheating, or maybe its damaged? I scraped off the top of the cylinders, tomorrow will pull the valves from the head and start cleaning that up. It kinda looks like there might be valve seats pressed in already? Can you guys go over the pictures and tell me what you think? I'll plan on measuring the cylinder diameter tomorrow just for my records and pulling out the rollers after I buy a stick with magnet on the end. Quit a lot of corrosion under the carbon build up on the cylinders, don't know if that is normal.




IMG_20220325_111123_rs.jpg
IMG_20220325_115451_rs.jpg
IMG_20220325_111311_rs.jpg
IMG_20220325_111332_rs.jpg
 
Last edited:
The valves need to come out to get a good look at the seats. The cylinder walls look blacker than I would expect, they need honing at least. Other than that, the valves and head dont look too bad.

Col
 
CakeBandit said:
Okay, thanks for that info. I'm leaning on having the local machine shop do them if those are not hardened seats already pushed in the pictures.

I did pull the head off today. I was right on with my diagnosis which I am happy, Intake [Edit]: Exhaust valve #1. The reason the valve is oval shaped I still don't know. It look like a coolant passage or two is completely blocked between #1 and #2 cylinder. I am going to post pictures, could somebody tell me what the discoloration is in the cylinder wall? I think I may have had a close call with overheating, or maybe its damaged? I scraped off the top of the cylinders, tomorrow will pull the valves from the head and start cleaning that up. It kinda looks like there might be valve seats pressed in already? Can you guys go over the pictures and tell me what you think? I'll plan on measuring the cylinder diameter tomorrow just for my records and pulling out the rollers after I buy a stick with magnet on the end. Quit a lot of corrosion under the carbon build up on the cylinders, don't know if that is normal.




View attachment 261732 View attachment 261733 View attachment 261734 View attachment 261735
Click to expand...

Clean the head up very carefully, and look for cracks.
The bores are suspect, a few marks, and they look very shiny, has someone been using synthetic oil?
And make sure you get a composite head gasket, those copper gaskets are rubbish,
 
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