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Post by raygyver on Feb 17, 2020 20:14:27 GMT -5
I have a big gash going through the gasket surface of the valve block. How do i share a picture on the forum? It's the only thing out of place that i can see
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Post by oldgeek on Feb 17, 2020 21:06:25 GMT -5
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Post by raygyver on Feb 17, 2020 21:51:14 GMT -5
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Post by 90GTVert on Feb 18, 2020 0:04:28 GMT -5
Hard to say definitely; but it does look like the head should be replaced because of the gash and it appears that the threads for the spark plug aren't good. Makes more sense to replace vs repair with most of these small heads.
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Post by jmkjr72 on Feb 18, 2020 5:57:40 GMT -5
Looks like some valve damage on the intake too
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Post by mikehailwood on Feb 18, 2020 6:18:54 GMT -5
Have the valves been tested for leaks (like with a solvent)?
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Post by raygyver on Feb 18, 2020 9:41:14 GMT -5
No i haven't done that. My knowledge is limited, i have ordered a goofit bore kit because i thought it was probably a worn piston or ring, but they look fine. Only thing is i got a cheap goofit kit that doesn't come with the head. I think I'll just order a new head and put it all back on. Am i right that if i replace all those parts with new gaskets, there's nowhere else where i could lose compression?
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Post by snaker on Feb 18, 2020 9:50:24 GMT -5
It appears that the gouge was made by someone goin jackhammer when removing the head. So if that happened during this removal, it would have nothing to do with any loss of compression you may have experienced. By the way how did you determine or will determine loss of compression?
My vote is on replacing all.
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Post by raygyver on Feb 18, 2020 10:24:41 GMT -5
The head came off with ease, so no having to pry it out. Definitely, i have just ordered all the parts and should be here tomorrow. I rented a compression tester and followed instructions, and it read 75 psi at peak. The only thing that could have given a false reading that i can think of, would be that the vacuum lime system is not all put together correctly, however i have no idea If that has anything to do with it all.
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Post by GrumpyUnk on Feb 18, 2020 14:13:14 GMT -5
That engine has some miles on it. I have not seen one with any where near that amount of deposits.
Were it mine, I would disassemble the valves, and inspect the valve seats and the sealing area on the valve tulip. You may find damage that would explain the loss of compression, or it is possible that the valve clearance needed to be adjusted. The clearance will close from design spec with age and wear. That prevents the valve from seating firmly and can cause loss of compression.
The gouge on the cylinder head may be improved by one of two methods. Well, 3 if you have access to aluminum welding. One would be to sand the surface of the cylinder head until you remove enough metal that the scratch is no longer a groove. Second would be to use an epoxy compound, such as JB Weld, to fill the gouge. You'd need one that was heat resistant. Third would be to MIG/TIG the surface, and then re-face it smooth again. Fourth would be to get a 'fiber' head gasket instead of the stamped steel ones that are common. I repeat a lot, but will say again I personally prefer the fiber gaskets as they can seal imperfections better than the steel(I think) and can give a few thousandths of extra clearance to lower the CR a bit from the level raised by a BBK and standard head. I'm not sure the '47mm' heads are worth getting. As I understand a groove is cut around the perimeter of the cylinder on the head, but the actual head CC volume and casting are not changed from stock.
Glancing back at the images, it appears (limited view) that the piston rings are not expanded out from the piston. They may be stuck in the ring grooves. That can happen due to gunky oil being left on when something was put in storage, excess head causing the piston to lose its spring 'tension' to expand, or wear on the rings. It is possible just replacing the rings with new might restore your compression. A set of rings for $4-5 and a base & head gasket, and it might just run like new. I would definitely remove and clean up the valves and seats, and fill the gouge with epoxy. I really believe that JB Weld would fill the gouge, and only the tip of the gouge would possibly be exposed to combustion. The surrounding aluminum of the head and cylinder would draw the heat of combustion away from the JB Weld, likely enough that it would survive with no problem. Cost is minimal... Definitely at least do a valve adjustment, or for sure do one if you replace all the head parts.
I have kept all the piston/cylinders from the BBK installs I have done. Don't know exactly what to do with them, but for sure could make engines run that would otherwise be considered scrap at minimal cost. I have at least one of those.
Many of these engines, in other words, can be repaired with mechanics wire, duct tape and JB Weld. They may not be pretty, but will work. Take a look at the youtube channel Samodel. He is a master at making something from nothing. I think Eastern Europe is his home, but nothing exactly says so. He has converted air-cooled Dios to water cooling, using ingenious methods. If you are interested in 'mechanicing' he's a good watch.
A compression tester can be misleading. I purchased a new unit that did not register the pressure, seemingly due to the small volume involved that would not 'twitch' the needle mechanism. Used my old gauge, and it represented pressure a LOT closer to real numbers. Be sure that your gauge is accurate and responsive. The ones hecho in china may be a bit 'rougher' in their construct, and not so close as would be desired.
75psi is actually close enough that the engine should start. Could be low on power, but should run. Many small gas engines develop lower compression than that, and will run. Of course, 90 psi or more would be better, but I think it would run @75.
Having a vacuum line disconnected would not affect pressure, and actually might allow more air into the cylinder to be compressed. It is reported that the throttle should be propped wide open to test, which would equate to a wide open vacuum line... but I think you can get usable numbers with the throttle closed. FWIW.
tom
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Post by raygyver on Feb 19, 2020 8:08:23 GMT -5
Thanks for all the information. The new parts are out for delivery so, I'll install and see what happens. Fingers crossed
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Post by raygyver on Feb 21, 2020 6:09:05 GMT -5
Alright, so i got the parts, consisting of the big bore kit. I got a new head too, but figured the rocker arm was fine, but it seems not to fit, so i think I'm getting a bigger one note. Also. There were two metal spacers between the valve head and the cylinder wall. Does anyone know what these are called and where i can get them? They were very weak and so stuck that i bent them taking them out of the old head. Pretty sure this is going to fire right up, can i go without those spacers if need be?
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Post by mikehailwood on Feb 21, 2020 7:06:17 GMT -5
Photo?
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Post by raygyver on Feb 21, 2020 7:24:38 GMT -5
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Post by GrumpyUnk on Mar 12, 2020 12:03:12 GMT -5
Those are alignment ferrules. They fit tightly into the head and the cylinder, or in this case, the head and the cam & rocker arm carrier. There should be two more at the base of the cylinder where it mounts to the block/crankcase, and two more at the top of the cylinder where the head is gasketed to the cylinder.
You do not want to leave them out. Without their precise(?) positioning, the cam chain could get side-loads which are not a good thing, as the connecting rod could also get the same.
tom
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