November 1969 h25 rebuild

Mini Bike & Go-Kart Parts

markus

Well-Known Member
#1
Takin care of business on the old H25 I bought off byron the other day.
E22A5661-38E0-47C0-A600-B3847A7C5966.jpeg 17330F5C-47EA-4827-BCFD-2A3F681F6D04.jpeg 96B6030A-D2B5-4F05-BBFD-D066DF58A8B1.jpeg CD25EF7A-D2FC-42A0-A7D5-6F89ABC8FD46.jpeg 62D1EF4E-6738-4904-A0B5-FE11F3F55691.jpeg

Just enough wear that it needs to go over bore, ordered a piston and rings for that but gotta wait till it comes in before I start that. In the meantime today I knocked out all the other block work items it needed. Lot of pitting on the exhaust valve seat so before I wasted my time cleaning I did a quick cut too see how bad it really was. Also found the intake guide to be still in spec but on the verge. I have OS valves on hand so it gettin one of those as well.
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gov shaft hole is buggered as well

C9518D51-D798-4D89-9B26-F7C15DAEA2C8.jpeg
 

markus

Well-Known Member
#2
Stripped the block, and reworked the mating surfaces to get them all true. Took .015 off the had while I was at it. For the valves I deburred the ports, then cut the intake guide for the oversize valve. Did the seat cuts in 3 angles and plugged the compression bypass port off. 56830972-CCC1-417B-BC2A-028389C1D4D4.jpeg AA83745D-AC18-4E45-ADB5-05A7708CCD79.jpeg

I also ran the ridge reamer to clean that up and make the boring go a little smoother when the piston comes in.

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For the gov shaft I did one of the bushing I fab up and seated it in the case.
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more to come…..
 

markus

Well-Known Member
#6
Just another “boring” day here in the sunshine state. C8611EFF-700A-4753-A009-9DF2CC9F448C.jpeg

this piston actually came with rings, that was not expected. I had ordered a set of the “ long life” ones that tec offered from another vendor so I am going to wait to have a look at those. The engines that used them used a steel bore as well in the parts book but I have never had a set…… and they were only like 8 bucks shipped.

I started to finally fish up an hs50 short block I had been rebuilding and a customers mess of an HS40 rolled in this afternoon as well so, it can wait a couple of days image.jpg
 

I74

Well-Known Member
#7
Just another “boring” day here in the sunshine state. View attachment 282964

this piston actually came with rings, that was not expected. I had ordered a set of the “ long life” ones that tec offered from another vendor so I am going to wait to have a look at those. The engines that used them used a steel bore as well in the parts book but I have never had a set…… and they were only like 8 bucks shipped.

I started to finally fish up an hs50 short block I had been rebuilding and a customers mess of an HS40 rolled in this afternoon as well so, it can wait a couple of days View attachment 282965
Am guessing the ''long life'' rings are probably some sort of '' moly'' ect. other than ''cast'' ??
 

markus

Well-Known Member
#8
Am guessing the ''long life'' rings are probably some sort of '' moly'' ect. other than ''cast'' ??
not really sure, there is no explanation in the book and only shown as being factory installed in like 10 engine versions (H25/30 only) for the mid/later 60's era. I did cross a few numbers to make sure they were in something comparable, (head, case/bore, and cam design) and they matched up to what I am working with. The pics of them look like one ring is maybe chromed. I am going to see if I can find anything in some of the older repair manuals I have to see if there is any mention of them.
 
#10
Stripped the block, and reworked the mating surfaces to get them all true. Took .015 off the had while I was at it. For the valves I deburred the ports, then cut the intake guide for the oversize valve. Did the seat cuts in 3 angles and plugged the compression bypass port off. View attachment 282886 View attachment 282887

I also ran the ridge reamer to clean that up and make the boring go a little smoother when the piston comes in.

View attachment 282888
For the gov shaft I did one of the bushing I fab up and seated it in the case.
View attachment 282889 View attachment 282890 View attachment 282891

more to come…..
What's the reamer you used for the valves? Thanks
 

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