Whitey's Engine Rebuild

Well putting Whitey's' engine back together has been a real learning experience. I'm the type that likes to understand exactly how stuff works. Diving into a project I've never tackled before does not scare me. After all, If I really screw it up, I can always go back and let someone who DOES know what they're doing, do it right. And in the meantime.... I've at least learned, what it is I'm paying someone else to do for me. Although not totally flying blind here (I have done this kind of stuff to smaller engines,... 2 stroke motorcycles, lawnmowers, etc.) I figured how hard could it be. Well it's not. Trust yourself. Read everything you can find. Take your time. Hey..this philosophy worked when I tackled the O/D tranny rebuild in Whitey and it turned out fine.
First things first. Measure everything, TWICE. I picked up a bore gauge (on EBay of course) so I could see what the bores were like. Were they straight? ...need an over bore? What? Measuring the bores I found cylinder #3 (that actually had the low compression) was amazingly in better condition than cylinders #2, & #4, that still had good compression.
Each graduation on the gauge is 0.0005". I used dial calipers to set a 'zero' on the gauge at 2.9000". In the photo above left, the bottom of the bore still measured 2.900+/-0001". Above right shows a cylinder reading near the top of the bore at 0.0012". So it's actually reading 2.9011".

75w_cyl_sketch.jpg (2779 bytes)

The Drawing at the left, is the positions in the bore where measurements were taken with the bore gauge. The letter measure 'concentricity, the numbers, the depth in the cylinder. I wanted to know if the cylinders were warped, and how 'oversized' they might be. I needed to know if I needed a bore and hone , or could get away with honing the cylinders and just installing new rings, etc etc.

The dimensions in the following tables are 2.900" PLUS (+) what's in the
table. That means the cylinder is 'oversize' by that amount

First measurements of the cylinders after initial piston removal.

Cyl #1	A	B	C	D
1	.0010	.0005	.0007
2	.0002	.0002	.0003
3	.0005	.0005	.0005
4	0	0	0

Cyl #2	A	B	C	D
1	.0012	.0010	.0007
2	.0010	.0012	.0002
3	.0012	.0012	.0005
4	0	0	0

Cyl #3	A	B	C	D
1	.0032	.0015	.0018
2	.0032	.0015	.0015
3	.0032	.0014	.0020
4	0	0	0

Cyl #4	A	B	C	D
1	.0035	.0015	.0025
2	.0035	.0010	0
3	.0030	.0010	.0005
4	0	0	0

rear 75w_honed_cyls1.jpg (14174 bytes) front of block

After honing, cylinders #1 (at the right) and #2 are looking good and are only at 2.902" worst case (0.002" over stock diameter) Something else to notice is the 'chaff' from the original block casting in the water passage between the left two cylinders in the above picture. I'm going to break out the rest of it to open up the full little triangle. This should allow a greater cooling water flow and will match the opening in the head. I'm going to do this in all the water passages.

front of block 75w_honed_cyls2.jpg (17754 bytes) rear

At the top of the #1 cylinder (upper left) you can just make out a small dark line about 3/8" below the top of the cylinder. Although I can't feel it with a fingernail, or see it on the bore gauge, I think I'll hone it just a bit more. The lines at the bottoms of the cylinders are at the original 2.9" even.

75w_honed_4streek.jpg (16433 bytes)

After initial honing of the cylinders to break the glaze on the walls and flatten them a bit, I noticed a problem. In the #4 cylinder. There was a very visible vertical 'groove' up the front face (towards the front of the engine). I could just barely feel it with my finger nail, and to the best of my abilities, the bore gauge said it was roughly 0.0007" deep. Much more visibly identifiable, than measurable because of the honing striations. After further honing this 'groove' has now almost completely disappeared.

After honing the cylinders (three times), I'm leaving it at these dimensions. (Plus I'm getting better at using the bore gauge)

Cyl #1	A	B	C	D
1	.0005	.0003	.0009	.0006
2	.0005	.0002	.0006	.0006
3	.0005	.0002	.0008	.0003
4	0	0	0	.0002

Cyl #2	A	B	C	D
1	.0015	.0009	.0015	.0010
2	.0015	.0006	.0012	.0006
3	.0010	.0005	.0013	.0006
4	0	0	0	0

Cyl #3	A	B	C	D
1	.0035	.0021	.0020	.0012
2	.0034	.0021	.0012	.0009
3	.0034	.0021	.0012	.0005
4	0	0	0	0

Cyl #4	A	B	C	D
1	.0033	.0022	.0019	.0015
2	.0030	.0021	.0012	.0012
3	.0030	.0020	.0012	.0010
4	0	0	0	0

So if you look closely at the two tables, (ignoring my lack of skill reading the bore gauge the first time) The second table by comparison, shows the cylinders to much more concentric. Using a glaze busting three leg stone hone in a power drill, barely removed 0.0005" from the walls of the cylinders.

<-previous next ->

©1987-2010 All material copyright© Teglerizer 1996-2008	last edited 3/15/08	hits since last reset