New Timing Belt Slips?

I just installed a new timing belt and timing belt tensioner in my 1991 240. She runs and is operating better than with the previous belt!

I was showing a friend yesterday when I noticed the marks on the belt had moved forward a few teeth from the mark on the cam gear. Is it possible for a belt to slip during operation, and if so what would cause this? I've checked and there is only a degree or two of slack on the belt.

The lines on the belt will only line up once, while you are setting the sprockets. After the engine turns over, that relationship is gone. The sprocket marks will still be aligned to their pointers if you turn the engine over until they line up.

2manyturbos said:

The lines on the belt will only line up once, while you are setting the sprockets. After the engine turns over, that relationship is gone. The sprocket marks will still be aligned to their pointers if you turn the engine over until they line up.

Click to expand...

That makes sense, I was just worried I did something wrong

2manyturbos said:

The lines on the belt will only line up once, while you are setting the sprockets. After the engine turns over, that relationship is gone. The sprocket marks will still be aligned to their pointers if you turn the engine over until they line up.

Click to expand...

Yeah, IIRC, it takes like ~36 rotations to get all the marks to match up again.

daniels740 said:

Yeah, IIRC, it takes like ~36 rotations to get all the marks to match up again.

Click to expand...

Actually...

Belt = 123 teeth
Crank gear = 19 teeth
Cam gear = 38 teeth
Cam dot starts facing Up
One crank rotation = Cam dot facing down (the wrong way)

Rotation / Crank belt mark position / Cam dot

0 / 1 / Up      << Start here.
1 / 20 / Dn
2 / 39 / Up
3 / 58 / Dn
4 / 77 / Up
5 / 96 / Dn
6 / 115 / Up
7 / 11 / Dn
8 / 30 / Up
9 / 49 / Dn
10 / 68 / Up
11 / 87 / Dn
12 / 106 / Up
13 / 2 / Dn
14 / 21 / Up
15 / 40 / Dn
16 / 59 / Up
17 / 78 / Dn
18 / 97 / Up
19 / 116 / Dn
20 / 12 / Up
21 / 31 / Dn
22 / 50 / Up
23 / 69 / Dn
24 / 88 / Up
25 / 107 / Dn
26 / 3 / Up
27 / 22 / Dn
28 / 41 / Up
29 / 60 / Dn
30 / 79 / Up
31 / 98 / Dn
32 / 117 / Up
33 / 13 / Dn
34 / 32 / Up
35 / 51 / Dn
36 / 70 / Up
37 / 89 / Dn
38 / 108 / Up
39 / 4 / Dn
40 / 23 / Up
41 / 42 / Dn
42 / 61 / Up
43 / 80 / Dn
44 / 99 / Up
45 / 118 / Dn
46 / 14 / Up
47 / 33 / Dn
48 / 52 / Up
49 / 71 / Dn
50 / 90 / Up
51 / 109 / Dn
52 / 5 / Up
53 / 24 / Dn
54 / 43 / Up
55 / 62 / Dn
56 / 81 / Up
57 / 100 / Dn
58 / 119 / Up
59 / 15 / Dn
60 / 34 / Up
61 / 53 / Dn
62 / 72 / Up
63 / 91 / Dn
64 / 110 / Up
65 / 6 / Dn
66 / 25 / Up
67 / 44 / Dn
68 / 63 / Up
69 / 82 / Dn
70 / 101 / Up
71 / 120 / Dn
72 / 16 / Up
73 / 35 / Dn
74 / 54 / Up
75 / 73 / Dn
76 / 92 / Up
77 / 111 / Dn
78 / 7 / Up
79 / 26 / Dn
80 / 45 / Up
81 / 64 / Dn
82 / 83 / Up
83 / 102 / Dn
84 / 121 / Up
85 / 17 / Dn
86 / 36 / Up
87 / 55 / Dn
88 / 74 / Up
89 / 93 / Dn
90 / 112 / Up
91 / 8 / Dn
92 / 27 / Up
93 / 46 / Dn
94 / 65 / Up
95 / 84 / Dn
96 / 103 / Up
97 / 122 / Dn
98 / 18 / Up
99 / 37 / Dn
100 / 56 / Up
101 / 75 / Dn
102 / 94 / Up
103 / 113 / Dn
104 / 9 / Up
105 / 28 / Dn
106 / 47 / Up
107 / 66 / Dn
108 / 85 / Up
109 / 104 / Dn
110 / 123 / Up
111 / 19 / Dn
112 / 38 / Up
113 / 57 / Dn
114 / 76 / Up
115 / 95 / Dn
116 / 114 / Up
117 / 10 / Dn
118 / 29 / Up
119 / 48 / Dn
120 / 67 / Up
121 / 86 / Dn
122 / 105 / Up
123 / 1 / Dn      << Crank okay, cam 180 off.
124 / 20 / Up
125 / 39 / Dn
126 / 58 / Up
127 / 77 / Dn
128 / 96 / Up
129 / 115 / Dn
130 / 11 / Up
131 / 30 / Dn
132 / 49 / Up
133 / 68 / Dn
134 / 87 / Up
135 / 106 / Dn
136 / 2 / Up
137 / 21 / Dn
138 / 40 / Up
139 / 59 / Dn
140 / 78 / Up
141 / 97 / Dn
142 / 116 / Up
143 / 12 / Dn
144 / 31 / Up
145 / 50 / Dn
146 / 69 / Up
147 / 88 / Dn
148 / 107 / Up
149 / 3 / Dn
150 / 22 / Up
151 / 41 / Dn
152 / 60 / Up
153 / 79 / Dn
154 / 98 / Up
155 / 117 / Dn
156 / 13 / Up
157 / 32 / Dn
158 / 51 / Up
159 / 70 / Dn
160 / 89 / Up
161 / 108 / Dn
162 / 4 / Up
163 / 23 / Dn
164 / 42 / Up
165 / 61 / Dn
166 / 80 / Up
167 / 99 / Dn
168 / 118 / Up
169 / 14 / Dn
170 / 33 / Up
171 / 52 / Dn
172 / 71 / Up
173 / 90 / Dn
174 / 109 / Up
175 / 5 / Dn
176 / 24 / Up
177 / 43 / Dn
178 / 62 / Up
179 / 81 / Dn
180 / 100 / Up
181 / 119 / Dn
182 / 15 / Up
183 / 34 / Dn
184 / 53 / Up
185 / 72 / Dn
186 / 91 / Up
187 / 110 / Dn
188 / 6 / Up
189 / 25 / Dn
190 / 44 / Up
191 / 63 / Dn
192 / 82 / Up
193 / 101 / Dn
194 / 120 / Up
195 / 16 / Dn
196 / 35 / Up
197 / 54 / Dn
198 / 73 / Up
199 / 92 / Dn
200 / 111 / Up
201 / 7 / Dn
202 / 26 / Up
203 / 45 / Dn
204 / 64 / Up
205 / 83 / Dn
206 / 102 / Up
207 / 121 / Dn
208 / 17 / Up
209 / 36 / Dn
210 / 55 / Up
211 / 74 / Dn
212 / 93 / Up
213 / 112 / Dn
214 / 8 / Up
215 / 27 / Dn
216 / 46 / Up
217 / 65 / Dn
218 / 84 / Up
219 / 103 / Dn
220 / 122 / Up
221 / 18 / Dn
222 / 37 / Up
223 / 56 / Dn
224 / 75 / Up
225 / 94 / Dn
226 / 113 / Up
227 / 9 / Dn
228 / 28 / Up
229 / 47 / Dn
230 / 66 / Up
231 / 85 / Dn
232 / 104 / Up
233 / 123 / Dn
234 / 19 / Up
235 / 38 / Dn
236 / 57 / Up
237 / 76 / Dn
238 / 95 / Up
239 / 114 / Dn
240 / 10 / Up
241 / 29 / Dn
242 / 48 / Up
243 / 67 / Dn
244 / 86 / Up
245 / 105 / Dn
246 / 1 / Up      <<< Yay! Back where we started.

DP.

MasterBlaster said:

DP.

Click to expand...

Is that why they call you MasterBlaster ?

OP:

If in fact the marks had slipped you'd certainly notice a drop off in performance.

The engine would not then run correctly.

MasterBlaster said:

Actually...

Belt = 123 teeth
Crank gear = 19 teeth
Cam gear = 38 teeth
Cam dot starts facing Up
One crank rotation = Cam dot facing down (the wrong way)

Rotation / Crank belt mark position / Cam dot
.
.
.
246 / 1 / Up      <<< Yay! Back where we started.

Click to expand...

I was just 210 rotations off