| ||||
| ||||
| Moderated by: Greg Fletcher |
|
||||||||||||||
| Timing belt change | Rate Topic |
| Author | Post |
|---|
| Posted: 06-28-2025 07:53 pm |
|
1st Post |
|
mgfaber53 Member
|
I'm changing the timing belt while I'm installing the Mikuni carbs. Is there a detailed procedure on the site for this process? I may also need to put new bearings in the tensioner. This is all new for me and I'm struggling with how to properly position the pistons and exactly how to do it. Okay, so I am unable to rotate crankshaft by turning the nut on the pulley. Am I missing something? Beside a functional brain? Last edited on 06-28-2025 10:30 pm by mgfaber53 |
||||||||||||||
| |||||||||||||||
| Posted: 06-29-2025 03:09 am |
|
2nd Post |
|
vnavaret Member 
|
You can use a socket on the crank pulley and perhaps a breaker bar after putting the gearbox in neutral. Instead of a socket, you can put the car in fourth gear and push the car while watching the crank pulley - I find this method the easiest as long as there is room to move the car. Get a copy of the shop manual for the procedure. If you are going to do your own maintenance, and it sounds like you are, you need the shop manual. Martin Robey sells the manual, as does the Jensen owners club. You can also get used copies on eBay. When positioning the cam sprockets, you need to replace the cam belt if there are any cracks or damaged teeth on the belt. Make sure that you put the correct sprocket on the correct cam - early sprockets are marked IN or EX for the intake or exhaust, later motors used interchangeable sprockets with two sets of marks. You must rotate the crank to position the number one cylinder at top dead center, then rotate the cams such that the timing marks point at each other. For early engines, the marks will be IN and EX. For later engines there will be two sets of marks - 110 and 115 each mark will have the letters IN or EX associated the number. For the intake cam, you use the number designated IN, and on the exhaust the number associated with the letters EX. You will need to decide whether to use the 110 marks, or the 115 marks. The 110 marks will give you more power, a slightly rougher idle, increased emissions and lower fuel economy. The 115 marks will give a smoother idle, broader power band, better economy and emissions, and slightly lower peak power. You will note that later pulleys have markings on both sides of the sprockets. Because of this, you can even mix and match the timing numbers of the sprockets, but whatever number you use, you must end up with IN on the intake cam aligned with EX on the exhaust cam. The ignition sprocket should have the "F" mark pointing at the center of the crankshaft sprocket. Note that the marks on the sprockets were changing over time to meet the changing emissions regulations. There were some sprockets with 100 and 110 timing marks. If you have these sprockets, you are supposed to set the 100IN mark aligned to the 110EX mark (North America only). Vance Last edited on 06-29-2025 03:14 am by vnavaret |
|||||||||||||
| ||||||||||||||
| Posted: 06-29-2025 03:22 am |
|
3rd Post |
|
mgfaber53 Member
|
Vance, thank you so much! I do have a shop manual,but didn't find it helpful with some of the issues I was having. Your information is much more useful. By pulling the spark plugs and dribbling a little ATF in the wells. I was able to break the crank free. The existing timing belt was in good condition, but I have a blue belt to replace it with just to be sure. I'm a fair shade treem mechanic, but the 907 is a completely different animal! Where in Oregon are you? I'm in Gladstone.
|
||||||||||||||
| |||||||||||||||
| Posted: 06-29-2025 01:15 pm |
|
4th Post |
|
noomg Member
|
"Break the crank free", can we assume the motor is not running? When you've got a problem the more detail and history you can provide the board the better the odds of solving your problem. Information like how long have you had it? Is it or has it been running since you've owned it? If the timing belt is good, why are you changing it? Do you know how old it is or how many miles it has on it? Just a few question off the top of my head that would be helpful. Also you want to change the carbs if the car is not running now it would be a good idea to get it up and running properly before you make the change. If for no other reason you'll be able to tell if there's any performance improvement. I hope you take these suggestions in the spirit in which they were given, apparently I unwittingly pissed off the last guy!
|
|||||||||||||
| ||||||||||||||
| Posted: 06-29-2025 09:47 pm |
|
5th Post |
|
mgfaber53 Member
|
Sorry, I was in a bit of a panic as I have a limited amount of time right now to work on the car. I have had the car for 4 years. It is a 1974, VIN 19024. The PO had rebuilt the engine, adjusted the valves, installed an aluminum radiator, fuel cell, and various bits and pieces. The stroms had not been rebuilt, and the engine ran very poorly. The carbs were leaking badly, so I bought a rebuild kit and put them on my workbench - and there they sat for about 3 years while life kept me away. When it came time to rebuild the carbs, I did some research and learned about the Mikuni conversion. Having a little extra in my toy stash, I purchased the kit. At the same time I had the distributor rebuilt, bought a new coil, plugs, etc., and the blue timing belt with hopes I would not have to change it again anytime soon. At 71 years old and still working full time, I don't need any more work than necessary. So at this point, I am ready to change the cam timing to 110/110 and install the belt, carbs, etc. The 907 is completely foreign to me, so I am looking to the club for advice as I go along. I am deeply appreciative of all the highly knowledgeable members whose posts I follow. Is that sufficient info?
|
||||||||||||||
| |||||||||||||||
| Posted: 06-29-2025 11:14 pm |
|
6th Post |
|
mgfaber53 Member
|
Okay, here is where things are now. Crank pulley is beyond TDC alignment. Intake cam is aligned at 110 IN. exhaust cam pulley is between 110 IN and 115 EX. Is the crank pulley misaligned?
|
|||||||||||||
| ||||||||||||||
| Posted: 06-30-2025 12:10 am |
|
7th Post |
|
vnavaret Member
|
mgfaber53 wrote: Okay, here is where things are now. Without a picture, it is difficult to say. Many have noted that they have a slight misalignment after setting things as close as they can. Without knowing how big a misalignment is meant by "beyond" and "between 110IN and 115EX" I cannot really be certain. I would ask this question: Is it possible to reduce the size of the errors if you remove the belt, reposition the sprockets, then reinstall the belt? If the answer is yes, the crank sprocket and the exhaust sprocket (at least) are misaligned. Vance Last edited on 06-30-2025 12:11 am by vnavaret |
||||||||||||||
| |||||||||||||||
| Posted: 06-30-2025 12:24 am |
|
8th Post |
|
mgfaber53 Member
|
I thought I had posted pics, apparently they did not go through. Is there a trick to it?
|
|||||||||||||
| ||||||||||||||
| Posted: 06-30-2025 04:14 pm |
|
9th Post |
|
mgfaber53 Member
|
Here are some pics. I hope I am not overstepping by asking for help.
|
||||||||||||||
| |||||||||||||||
| Posted: 06-30-2025 04:17 pm |
|
10th Post |
|
mgfaber53 Member
|
Still trying to post pics
|
|||||||||||||
| ||||||||||||||
| Posted: 06-30-2025 06:38 pm |
|
11th Post |
|
vnavaret Member
|
JHPS is very fussy about pics. It will not accept photos larger than 102kb. If you are taking photos with your phone they are probably about 4MB in size, much too large. You will need to take the photos from your phone, and use your favorite photo editing application to resize them down under the 102kb limit. Then you can attach them to your post. You are only allowed one photo per post, so if you have more than one photo to share you must make one post for each photo. Vance
|
||||||||||||||
| |||||||||||||||
| Current time is 04:27 am | |
| > Jensen Healey & Jensen GT Tech > Ignition > Timing belt change | Top |
