9 replies to this topic

[StevenTempered]

After a recent drop in top end power on my 1293, I checked the compression and I'm getting 145, 140, 140, and 160.

The notes on the engine build that were given to me when I bought it say it is a 10.5:1 compression ratio, which from what I've read should be getting over 200psi. 

 

It's fairly obvious from the engine that the head gasket needs replacing, but is this itself enough to explain such a drop in pressure? Or should I also be looking to replace the piston rings as well? The engine supposedly only has about 10,000 miles on it.

[panky]

Those reading look more like the valves need lapping in, if the head gasket had gone one or more cylinders would be virtually zero. It could be something a simple as the valve clearances closed up, try re-setting them and re- test before diving in. Also try a dribble of oil down the bores and test again, any significant increase in pressure would point to worn rings.

Also when you do the compression test do it with a warm engine, fully charged battery and throttle wide open. Out of interest what kind of compression tester are you using, there's a lot of dodgy ones for sale on eBay.

[slidehammer]

If you know the head gasket is faulty, then you must rectify that before you can decide on the state of the bores etc. With the head off you will be able to see if the is a wear step on the top of the bores, due to ring wear. Also you would be wise to decoke the head and lap in the valves and retry the compression test.

[StevenTempered]

Think my pressure tester probably did come off ebay, but I've had it a while and it's tried and tested on a few old bikes. I'll order a new gasket set and hopefully take the head off next weekend, lap the valves, and retry. 

 

My knuckles are healing from last week when I replaced the clutch hydraulics, so it's probably time I got my hands dirty again.

 

Cheers.

[sonikk4]

As mentioned do a leak down test first before you strip the engine down. That way you will get a definitive answer rather than taking a punt.

[carbon]

After a recent drop in top end power on my 1293, I checked the compression and I'm getting 145, 140, 140, and 160.

The notes on the engine build that were given to me when I bought it say it is a 10.5:1 compression ratio, which from what I've read should be getting over 200psi. 

 

It's fairly obvious from the engine that the head gasket needs replacing, but is this itself enough to explain such a drop in pressure? Or should I also be looking to replace the piston rings as well? The engine supposedly only has about 10,000 miles on it.

 

Steve - you say it's obvious that the head gasket needs replacing. Are there other signs such as water in the oil or oil in the coolant?

 

Your cylinder pressures are fairly consistent, if the head gasket goes it's often between cylinders 2 & 3 and then you get very low readings on 2 and 3 but 1 and 4 would be fairly close to normal. And in my experience a blown head gasket gives a very noticeable drop in power right throught the rev range.

[StevenTempered]

 

After a recent drop in top end power on my 1293, I checked the compression and I'm getting 145, 140, 140, and 160.

The notes on the engine build that were given to me when I bought it say it is a 10.5:1 compression ratio, which from what I've read should be getting over 200psi. 

 

It's fairly obvious from the engine that the head gasket needs replacing, but is this itself enough to explain such a drop in pressure? Or should I also be looking to replace the piston rings as well? The engine supposedly only has about 10,000 miles on it.

 

Steve - you say it's obvious that the head gasket needs replacing. Are there other signs such as water in the oil or oil in the coolant?

 

Your cylinder pressures are fairly consistent, if the head gasket goes it's often between cylinders 2 & 3 and then you get very low readings on 2 and 3 but 1 and 4 would be fairly close to normal. And in my experience a blown head gasket gives a very noticeable drop in power right throught the rev range.

 

 

There's a lot of oil residue around the gaskets on the engine and it smokes a lot when cold.  Which has always been the case to some extent, but it's definitely drinking a bit more oil lately.  The coolant looks pretty clean though.

 

From the advice in this thread, I am leaning toward thinking the valve clearances and laping may be the main culprit, but the gasket can't be helping and if I'm re-lapping the valves the gaskets will need replacing anyway.

 

It's definitely lost power across the band since I bought it, but it's particularly noticeable at the top end, where it's struggling to rev past about 4.5-5k on the motorway.

[cal844]

 

After a recent drop in top end power on my 1293, I checked the compression and I'm getting 145, 140, 140, and 160.
The notes on the engine build that were given to me when I bought it say it is a 10.5:1 compression ratio, which from what I've read should be getting over 200psi. 
 
It's fairly obvious from the engine that the head gasket needs replacing, but is this itself enough to explain such a drop in pressure? Or should I also be looking to replace the piston rings as well? The engine supposedly only has about 10,000 miles on it.

 
Steve - you say it's obvious that the head gasket needs replacing. Are there other signs such as water in the oil or oil in the coolant?
 
Your cylinder pressures are fairly consistent, if the head gasket goes it's often between cylinders 2 & 3 and then you get very low readings on 2 and 3 but 1 and 4 would be fairly close to normal. And in my experience a blown head gasket gives a very noticeable drop in power right throught the rev range.
 

 
There's a lot of oil residue around the gaskets on the engine and it smokes a lot when cold.  Which has always been the case to some extent, but it's definitely drinking a bit more oil lately.  The coolant looks pretty clean though.
 
From the advice in this thread, I am leaning toward thinking the valve clearances and laping may be the main culprit, but the gasket can't be helping and if I'm re-lapping the valves the gaskets will need replacing anyway.
 
It's definitely lost power across the band since I bought it, but it's particularly noticeable at the top end, where it's struggling to rev past about 4.5-5k on the motorway.

Once you remove the head, make sure you degrease the head before starting to lap the valves... Also check the seats, are they hardened?

[gazza82]

Smoking when cold could be valve seals failing to prevent oil from dribbling down the guides. But if you are going to lap the valves they will need to be replaced anyway.

[Magneto]

I agree with doing a leakdown test first, then you'll know what you're really dealing with rather than throwing parts and money at it......